Q & A

Answers to questions sent to me via email.

Why is buried surface hoar so dangerous?
Buried surface hoar is dangerous because surface hoar crystals form a thin layer that contains a lot of air. This means that the layer on top of the surface hoar is mostly supported by air. When crushed, surface hoar crystals have the capacity to rearrange themselves into a much smaller space, which causes the layer above to fall. As the layer falls, it provides energy that causes the crushing to spread. After the crushing process is complete, you're left with two layers of snow that have no attachment to each other-delamination has occurred. Finally, gravity, which is always in effect, pulls the detached layer downhill.

All the persistent forms ( facets, depth hoar, surface hoar, and combinations of these with crusts ) are dangerous for this reason. Crusts, when found alone, are dangerous for slightly different reasons, mostly related to poor bonding at the interface between the crust and the layer above-poor bonding increases the risk of catastrophic delamination, and catastrophic delamination is required for avalanche formation. The answer provided here intentionally does not discuss weak layer parameters such as anisotropy or variations in grain morphology, which are more related to why the layers are persistent than to why they are dangerous.

What is the significance of snow crystal size?
There are two key factors related to crystal size: the first factor is that large crystals have a lower number of bonds per unit volume. This is part of the reason why the persistent forms, such as facets and surface hoar, are so weak. Networks of large crystals can be quite strong, but they are almost always relatively weaker than networks of smaller crystals.

The second factor is grain size mismatch between layers. Grain size mismatches result in weaker bonding between layers, because the smaller grains overlay the pore space between the larger grains. This means a lot of the smaller grains are simply "touching the air". Furthermore, such configurations tend to concentrate stress at the interface between the layers.

What wind speed produces wind slab?
This depends almost entirely on the condition of surface snow. It takes little more than a stiff breeze to move dry, loosely packed snow. On the other hand, hurricane force winds will have little effect on dense, frozen corn snow.

What is the source of uncertainty in persistent weak layers?
With respect to persistent weak layers, uncertainty arises from a few key factors:

• Where is the weak layer?
• What is its depth below the surface?
• How weak is the layer and surrounding interfaces?

Picture a mountain valley. You know that there is buried surface hoar in some places. You also know that its depth below the surface varies. You also know that its degree of weakness varies by location.

Now that we've discussed what you know, think about what you don't know.

Snowpack Synopsis for British Columbia Interior Ranges

A great read from James Floyer.

http://www.avalanche.ca/cac/library/researchandarticles/2011-01-06_Snowpack_Synopsis

Enjoy!

Forecasting 101

if I knew then, what I know now—from the vernacular

There are lots of options for improving your avalanche forecasting skills, but what happens after you've taken an avalanche safety training course? The idea is to get out and gain experience, but the relationship between experience and skill is tenuous. Yes, you need to get out and ski tour, but you also need to focus on increasing your skill, so that all your hard-earned experience doesn't go to waste.

I get a few emails each month in which people ask me how to break past a learning plateau, and my answer is, increasingly, to engage in some self-directed study. Of course, the question then becomes what should I study?

When I think about all things I've learned about avalanches, several things really stick out as useful. Snow metamorphism is one of the most useful topical areas, and of course, learning the best practises of risk management is also really useful. You should also study avalanche formation because the information you learn is incredibly useful when interpreting snowpack test results. Of course, all this leads in the general direction of improving your backcountry avalanche forecasting skills, and there is one resource that is utterly peerless in this regard.

Chapter six of The Avalanche Handbook lays out a theoretical framework for avalanche forecasting that I've found very useful. The elements of applied avalanche forecasting are as follows:

• Definition. Forecast snowpack instability across space and time.
• Goal. Align your perception of instability with reality.
• Information Types & Relation To Perception. The relationship between instability and Class III, II, and I factors.
• Scales in Space and Time. Considering avalanche forecasting in terms of spatial and temporal parameters.
• Human Factors and Perception. Managing your state of mind and remaining objective.
• Reasoning Processes. Learn how to apply inductive and deductive reasoning to the problem.
• Decision-Making. How to manage risk.

When I first read this chapter, my mind certainly did a few backflips and double-takes. How do you take something this complex and apply it in the real-world? After a few more reads, and after some directed study of the material, including extensive Q & A, I finally was able to wrap my brain around the concepts.

I'm prepared to make a fairly steep claim in this post, and it is as follows: there is no better way to learn how to forecast avalanches than to study the material in this chapter until you know it forwards and backwards. Naturally, I've prepared an exam that you can use to gauge your progression.

Elements of Avalanche Forecasting Exam

124 questions from chapter 6 of The Avalanche Handbook. As with my other exams: Yes, I am fully aware that this exam is ridiculous, but it was a lot of work, so have fun.

Capsule

This chapter discusses avalanche forecasting. The seven elements of avalanche forecasting are discussed, as well as the basis for each. The elements of forecasting are linked through risk concepts ( especially perception / perceptual errors related to data sampling ) to form a framework suitable for learning basic forecasting. Specific forecasting techniques and procedures are not included because, given the multitude of forecasting contexts and the dynamic, evolutionary nature of the forecasting process, there is not really a specific process used to issue a forecast. At the end of this chapter you should understand the basis for avalanche forecasting, data types, human perception, and the links between these forecast components and risk concepts such as error, probability, and decision-making.

List Of Sections

1. Forecasting And Avalanche Forecasting.
   This section contains a detailed overview of forecasting, avalanche forecasting,
   and including relevant details on methods and pitfalls.
2. The Seven Elements Of Avalanche Forecasting.
   This section contains in-depth analysis of each element of avalanche forecasting.
3. Common Biases And Decision Traps In Avalanche Forecasting.
   This section contains an in-depth explanation of biases and decision traps, along
   with techniques to neutralize these biases and avoid decision traps.

Forecasting And Avalanche Forecasting

1. Around what element is modern avalanche forecasting framed? From what perspective are forecasts issued?
2. List all seven elements of applied avalanche forecasting.
3. Avalanche forecasting is a ________ problem.
4. All seven elements are ________.
5. Most avalanche accidents occur as a result of human errors. True or False.
6. Provide the definition of forecasting.
7. Define the root cause of most avalanche accidents.
8. How is avalanche forecasting linked to risk analysis?
9. Is avalanche forecasting limited only to estimates of instability? Explain why or why not.

I. Definition Of Avalanche Forecasting

1. Define avalanche forecasting.
2. Define the major physical uncertainty with respect to avalanche forecasting.
3. Avalanche forecasting is defined in terms of ________.
4. Whereas traditionally, avalanche forecasting was defined in terms of ________.
5. In avalanche forecasting, what type of information is most highly prized?
6. To what does triggering level refer?
7. Provide three examples of types of forecasting relative to triggers.
8. How do most slab avalanches release?
9. Some avalanches release without the need for an external trigger. True or False.
10. If true, explain. If false, explain.
11. Upon what does the energy required to release a slab avalanche depend?
12. What is the primary reason avalanche forecasting is probabilistic, with a risk-based character?

II. Goal Of Avalanche Forecasting

1. Define the goal of avalanche forecasting. Discuss the primary sources of uncertainty.
2. State the goal of avalanche forecasting from the human perspective.
3. How is this goal accomplished?
4. Define relevant information in the context of avalanche forecasting.
5. There is a strong link between quantity of information and accuracy of decisions. True or False.
6. There is a strong link between confidence in a decision and the resulting accuracy. True or False.
7. Briefly discuss the role of redundant information in statistical predictions.
8. List and describe each data classification.
9. Discuss ensemble forecasts.

III. Human Factors And Perception

1. Discuss the scale of failure in human perception with respect to avalanches.
2. Define perception.
3. Discuss the two general components of human influences.
4. Connect risk-taking propensity to perception.
5. What relationships does the Risk-Decision Matrix display?
6. Define Operational Risk Band [ ORB ].
7. What is the upper boundary of the ORB?
8. What is the lower boundary of the ORB?
9. Provide a list of Type I errors.
10. Provide a list of Type II errors.
11. Define target risk.
12. What are the consequences of Type I errors.
13. What are the consequences of Type II errors.
14. What is the relationship between uncertainty and perception?
15. Who coined the term risk homeostasis?
16. Explain risk homeostasis and provide an example.
17. List two or three items that improve perception.
18. List two or three items that degrade perception.
19. When might biases have a small effect on perception of instability?
20. When might biases have a large effect on perception of instability?
21. Discuss absolute instability relative to perception.
22. Discuss conditional instability relative to perception.
23. Write a brief explanation of the implications of perception of instability and the public danger scale.
24. Draw the continuum of instability and describe perception at three points.
25. Why is the link between data sampling and perception so important?
26. What does White ( 1974 ) argue about perception of hazard?
27. What is shown by statistics that compare fatalities to the public danger scale?
28. Why is perception better for instability in new snow?
29. Is randomness desired in the sampling process for avalanche forecasting?
30. Why are slopeside stability tests sometimes compared to playing the lottery?

IV. Reasoning Processes

1. Define the two main types of reasoning used in avalanche forecasting.
2. Provide an example of each type of reasoning.
3. Snow stability is dynamic and evolutionary, therefore avalanche forecasting is ________ and evolutionary.
4. What underpins the dynamic nature of avalanche forecasting?
5. The dynamic process of ________ ________ about instability using ________ ________ is somewhat analogous to ________ ________ using ________ ________ as ________ ________.
6. For a given avalanche path, when does the ideal forecast period begin?
7. Explain the answer to the previous question, in the context of forecast revision.
8. Define Bayes Theorem.
9. In avalanche forecasting, relative to Bayes Theorem, what constitutes the prior?
10. In avalanche forecasting, relative to Bayes Theorem, what constitutes the likelihood?
11. In avalanche forecasting, relative to Bayes Theorem, what constitutes the posterior?
12. Discuss the relationship between inductive reasoning, datums, and forecast revisions relative to instability.
13. How does an avalanche atlas fit into the context of avalanche forecasting as a Bayesian process?
14. In the context of avalanche forecasting, instability is not highly time-dependent. True or False.
15. If this is false, explain why.
16. List three examples of the deductive elements of avalanche forecasting.
17. Compare the evolutionary character of reasoning for helicopter backcountry skiing and ordinary backcountry skiing.

V. Information Types And Relation To Perception

1. Information for avalanche forecasting consists of two types. Explain each and include examples.
2. Should one always have an opinion about instability before attempting risky activities in avalanche terrain?
3. Describe the correct course of action if information relevant to the case at hand is missing at the beginning of a forecast period.
4. Describe a method to implement the correct course of action for the previous question.
5. If avalanche forecasting is Bayesian, what information type constitutes the likelihood?
6. If avalanche forecasting is Bayesian, what information type constitutes the prior?
7. Can data derived from computer models constitute the prior?
8. Define informational entropy.
9. Why is wind speed and direct data harder to interpret than cracking of the snow cover?
10. Define highly correlated.
11. What is necessary for dealing with highly correlated data?
12. Does the class of information ( I, II, III ) always give the most priority to Class I information?
13. Describe the theory of weighting data.

VI. Scales In Space And Time

1. Define spatial scale relative to avalanche forecasting.
2. Define temporal scale relative to avalanche forecasting.
3. Define scale-matching.
4. Provide an example of what might happen if scale-matching is not performed.
5. Explain the three primary spatial scales.
6. Difficulty of forecasting is inversely proportional to scale. True or False.
7. If true, explain. If false, explain.
8. Does failure to perform scale-matching result in many needless accidents?
9. Define now-cast.
10. Which is more difficult: forecasting stability for next Wednesday or next Thursday?
11. Why does chaos influence avalanche forecasting?

VI. Decision-Making

1. Provide a basic list of steps used to issue an avalanche forecast.
2. Why formalize the decision-making process?
3. Relative to avalanche forecasting, what underpins the fundamental residual risk with all decisions?

Conclusions

1. Why is a chain of events difficult to construct for avalanche forecasting?
2. Where do terrain and snow climate fit into the avalanche forecasting?

Biases

1. Discuss "search for supportive evidence" and how to neutralize this bias.
2. Discuss "inconsistency" and how to neutralize this bias.
3. Discuss "conservatism" and how to neutralize this bias.
4. Discuss "recency" and how to neutralize this bias.
5. Discuss "frequency" and how to neutralize this bias.
6. Discuss "availability" and how to neutralize this bias.
7. Discuss "illusory correlations" and how to neutralize this bias.
8. Discuss "selective perception" and how to neutralize this bias.
9. Discuss "expert halo" and how to neutralize this bias.
10. Discuss "underestimating uncertainty" and how to neutralize this bias.
11. Discuss "excessive optimism" and how to neutralize this bias.
12. Discuss "anchoring" and how to neutralize this bias.
13. Discuss "rules of thumb" and how to neutralize this bias.
14. Discuss "guide-client relationship" and how to neutralize this bias.
15. Discuss "social proof" and how to neutralize this bias.

Chapter 6 Exam Answers

245 answers to questions from chapter 6 of The Avalanche Handbook.

Forecasting And Avalanche Forecasting

1. Modern avalanche forecasting framed around instability and conducted from the perspective of the trigger.
2. The seven elements of applied avalanche forecasting are as follows:
   
   • Definition
   • Goal
   • Human Factors And Perception
   • Reasoning Processes
   • Information Types & Relation To Perception
   • Scales Of Space And Time
   • Decision-Making
3. Avalanche forecasting is a dynamic problem. Forecasting avalanches
   means dealing with uncertainty in the form of spatial and temporal variability
   in the seasonal snowpack, including incremental in snow and weather conditions.
4. All seven elements are interconnected.
5. True. Most victims trigger the avalanche themselves. This suggests that the
   perception ( i.e. "the snow is stable" ) did not match reality at the time of the
   accident.
6. Forecasting is the prediction of current and future events.
7. Errors in human perception are at the root of most avalanche accidents.
8. The link between avalanche forecasting and risk analysis is formed when
   decision-making follows the prediction issued by an avalanche forecast. Since
   these decisions involve a chance of losses, the process of avalanche forecasting
   and the resulting decision-making is the equivalent of a risk analysis.
9. Avalanche forecasting is not limited to estimates of instability. There is
   a connection between avalanche forecasting, decision-making, and the inherent risk
   of those decisions.

I. Definition Of Avalanche Forecasting

1. Avalanche forecasting is the prediction across space and time of
   current and future snowpack instability relative to a specific triggering level.
2. The spatial and temporal variability of the seasonal snow cover is the
   principle physical uncertainty in avalanche forecasting.
3. Avalanche forecasting is defined in terms of instability.
4. Whereas traditionally, avalanche forecasting was defined in terms of stability.
5. Information that reveals instability.
6. Triggering level refers to the amount of energy required to release an avalanche.
7. Forecasting for natural releases, forecasting for skier triggering, forecasting for explosive triggering.
8. Most slab avalanches release from overloading by precipitation or wind.
9. True.
10. Sometimes slabs release due to temperature change. Temperature change ( usually an increase )
    results in slab motion which leads to deformation. If there are pre-existing weaknesses such
    as slip surfaces or shear bands, the additional deformation produces the propagating shear
    fractures required to release an avalanche.
11. The energy required to release a slab depends largely on the size of imperfections and
    the parameters of the load applied at any given time. In this case, parameters of load applied means
    intensity, which is expressed roughly by the amount of force and the rate at
    which the force is applied ( the balance between shear stress intensity
    and shear fracture toughness in the weak layer ).
12. At all times, but especially during times of conditional instability ( the
    prevailing state ), the size, state, quantity, and distribution of weaknesses and
    imperfections ( such as weak zones and weak interfaces ), and the energy required to
    trigger a slab release on any such weakness, are unknown. Therefore avalanche forecasting
    can be reduced to encounter probability and trigger probability, i.e.
    "what is the chance of encountering a critical imperfection and how much energy
    will it take to trigger an avalanche". These probabilities give avalanche forecasting
    its risk-based character.

II. Goal Of Avalanche Forecasting

1. The goal of avalanche forecasting is the reduction of uncertainty introduced
   by three key sources:
   
   • Temporal and spatial variability of the snow cover, including terrain influences.
   • Incremental changes to the snowpack from snow and weather conditions.
   • Human factors, especially variations in perception.
2. From the human perspective, avalanche forecasting seeks to align perception
   and reality, i.e. human perception of instability across the spatial and temporal
   scales should match reality as closely as possible.
3. Aligning human perception with reality is accomplished by performing objective
   analysis on data relevant to the case at hand ( using the scientific method ).
4. In the context of avalanche forecasting, relevant information is any information
   that reveals instability.
5. False.
6. False.
7. Redundant information degrades the accuracy of predictions.
8. Data classifications are as follows:
   
   • Class I. Instability Factors. Non-numerical, mostly observable phenomena.
     Includes avalanche occurrences, shear quality, instability tests, cracking of the
     snow cover, and whumpfing.
   • Class II. Snowpack Factors. Rule-based. Snow stratigraphy, snow temperature,
     grain size and type, snow density.
   • Class III. Snow and Weather ( meteorological ) Factors. Precipitation, wind,
     temperature, radiation, weather forecast.
9. An ensemble forecast is the average of several predictions. It is thought that
   ensemble averages are more accurate. These forecasts are often used as a hedge against
   chaos. Ensemble forecasts have improved weather forecasting.

III. Human Factors And Perception

1. Failures in human perception with respect to avalanches run from the
   level of individual to the level of government and
   society. It is possible for a single individual to experience a
   serious perception failure and trigger an avalanche while skiing. On the
   other end of the scale, it is possible for an entire society to experience
   a serious perception failure and fail to allocate sufficient resources to
   avalanche forecasting, hazard mapping, and zoning.
2. Perception is a view of reality based on information processing by
   the senses.
3. Human influences on perception are roughly divided into the following categories:
   
   • Basic personality traits and behaviour ( risk propensity ).
   • Individual perception and its effect on decision-making.
4. The relationship between risk propensity and decision-making is highly
   complex, but in general risk-taking propensity is governed by the total
   sum of one's life experiences.
5. The Risk-Decision matrix displays the relationship between
   risk propensity, perception, and decision-making.
6. The operational risk band is a framework defined
   by the upper and lower limits of risk. To avoid errors that
   result in either accidents or excessive conservatism, the results
   of all decisions should fall inside the operational risk band. This
   is an important component of formalized decision-making.
7. The upper limit of the ORB is a Type I error, usually resulting in an accident.
8. The lower limit of the ORB is a Type II error, usually resulting in lost opportunity.
9. Reluctance to claim the snowpack is unstable unless hard proof is at hand.
10. Failure to open an important transportation corridor.
11. Target risk is the maximum risk an individual is willing to accept for
    a given reward. Target risk optimizes the difference between potential gains
    and potential losses. Behaviour modification is the typical method
    by which people seek to achieve target risk. For example, people might
    be willing to take a serious risk for a serious reward but usually are
    unwilling to take a serious risk for a small reward. Achieving target risk
    means that options are weighed based on the difference between risk and the reward
    across the series of options, with the option having the largest difference chosen
    most frequently. ( Relative to the individual and their risk propensity,
    which is of course, a complex subject by itself ). In the bigger picture,
    it is extremely important to understand how one's perception of risk and reward,
    influence decision-making. The ORB is a framework used
    to formalize decision-making with customizable upper and lower limits on risk.
    The upper and lower limits are set by an organization. ( Or an individual although
    most individuals probably do not consciously consider the ORB in their decision making process. )
12. Death, accidents, injuries.
13. Serious financial losses, lost opportunities, bruised egos.
14. Variations in perception increase with uncertainty.
15. Gerald Wilde
16. When safety devices are used, people modify their behaviour to
    maintain the same level of risk as before. When avalanche beacons
    are used, people choose to ski riskier terrain than they would ski
    without an avalanche beacon. Therefore the overall level of risk
    remains the same. The long and the short of this effect is that
    using a safety device will affect your decision-making and this awareness
    is a critical element of objective decision-making.
17. Targeted education and experience improve perception.
18. Biases degrade perception.
19. Biases have a small effect on perception of instability
    when instability is widespread and the triggering energy is low.
20. Biases have a large effect on perception of instability when
    instability is not quite isolated and the triggering level is a
    bit higher than usual.
21. During times of absolute instability, most people, especially
    experienced people, agree that the snowpack is unstable. Therefore
    variations in perception are small.
22. During times of conditional instability ( the prevailing state ),
    people may or may not agree about the quantity or location of instability, nor
    about the required triggering energy. Therefore variations in perception
    are large.
23. Perception of instability relative to the public danger scale clearly
    shows that many fatalities are linked to the Considerable danger level, which
    proves that perception during conditional instability is poorest ( or
    has the largest variations, depending on your perspective ).
24. Diagram omitted.
25. Data sampling is one of the most crucial inputs into any forecast. In fact,
    it is fair to say that data sampling forms the basis of forecasting,
    especially for backcountry travel. Therefore, if the data sampling is subject
    to bias, the forecast is not objective. For example, if a slopeside test
    reveals nothing about instability, it can be easy to conclude that instability
    is not present. However the choice of test location plays a critical role in
    the test results. This is a perfect example of how biased data sampling
    could lead to a disaster.
26. White argues that perception of hazard does not improve with the level of general education, i.e., high school graduates vs. college graduates.
27. Most accidents occur during Moderate or Considerable danger.
28. Storm snow instabilities are found near the surface; this type of
    instability is much easier to find or detect through skiing. Storm
    snow instabilities are also subject to far less perceptual error than
    deep instabilities because biases strongly affect deep instabilities,
    especially when instability persists for a long time. ( i.e. Recency or Frequency. )
29. No
30. The temporal and spatial variability of the snowpack, in addition
    to the danger of accessing real avalanche starting zones, often mean
    that the results of slopeside tests are, for all intents and purposes,
    random or chaotic ( like the lottery ). In addition, data sampling is
    subject to bias ( leading to serious perceptual errors ) that can add an element of
    Russian Roulette. In this case, not only might you "not win" any money,
    you also might suffer serious injury or loss of life.

IV. Reasoning Process

1. The two main types of reasoning used in avalanche forecasting are as follows:
   
   • Inductive. Inductive reasoning is intuitive and integrative; much more
     difficult to characterize than deductive reasoning. ( The inductive
     reasoning process differs from person-to-person. ) Inductive reasoning
     relies on a conclusion to establish a truth.
   • Deductive. Deductive reasoning relies on models, procedures, and
     data to arrive at a result. Deductive reasoning relies on a truth to
     reach a conclusion.
2. An example of each type of reasoning is as follows:
   
   • Inductive. Looking a steep slope that has shed its snow
     after a storm and understanding why the slope is safe to ski.
   • Deductive. Examining weather station data.
3. Snow stability is dynamic and evolutionary, therefore avalanche forecasting is dynamic and evolutionary.
4. Rapid changes to the snowpack, across both space and time, underpin the dynamic nature of avalanche forecasting.
5. The dynamic process of integrating information about instability using inductive reasoning is somewhat analogous to Bayesian revision using updated information as time proceeds.
6. With the first snowfall of the season. However, an avalanche atlas that contains
   historical information about the path is also very useful in assembling probabilities
   used in forecasting.
7. New information can make previous information worthless; since avalanche
   forecasting is dynamic and evolutionary, the process of forecast revision is
   on-going. However all new information, including information that reveals
   instability, must be integrated into the complete seasonal forecast, including
   any historic data available.
8. The definition of Bayes Theorem is as follows:
   
   • Posterior a Likelihood × Prior and proportional to
9. The previous forecast constitutes the prior if avalanche forecasting is viewed
   as a Bayesian process.
10. Singular information relevant to the current situation constitutes the likelihood
    if avalanche forecasting is viewed as a Bayesian process.
11. The new forecast constitutes the posterior if avalanche forecasting is viewed as
    a Bayesian process.
12. One datum can completely change the opinion of the outcome if the datum
    reveals information about instability. This is particularly true if a low-entropy
    ( low uncertainty ) datum reveals instability. For example, forecasting is conducted
    before a ski trip and moment-by-moment during the trip. Even if the current forecast
    is "isolated instability", the appearance of cracks beneath the skis changes the
    entire forecast immediately. In this case the current forecast is revised from "isolated
    instability" to "high instability" regardless of the prior forecast and the posterior
    ( the prediction ) is revised to "avalanche" from "no avalanche".
13. An avalanche atlas constitutes distributional information ( the prior ) in the
    context of avalanche forecasting.
14. False.
15. Instability is highly time-dependent; for example, solar warming
    can increase instability for a few hours during the afternoon. Instability may
    fall almost immediately when the slope falls into shade.
16. Information from models, rules-based systems, and telemetry data.
17. The information database for helicopter skiing is very deep and detailed.
    Information on prior seasons is available as well. For ordinary backcountry skiing,
    the information database is much smaller and relatively little historical information
    is available.

V. Information Types And Relation To Perception

1. Avalanche forecasting relies on the following types of information:
   
   • Singular Information. Information relevant to the current situation and near future.
   • Distributional Information. Information from the past or from similar situations in the past.
2. Yes
3. Go find the information.
4. Go test ski a few slopes, dig a few snow pits, read current telemetry and weather forecasts.
5. Yes
6. Informational entropy refers to the level of uncertainty associated with
   any data. Relative to avalanche forecasting, both cracking in the snow cover
   and natural avalanche releases provide extremely reliable, i.e. low uncertainty,
   information about instability. On the other hand, a report of wind speed and
   direction is indirectly linked to instability. Understanding and linking concepts
   is required to convert high entropy data into low entropy data.
7. Cracking of snow cover is an obvious sign of instability; cracks mean
   that propagating shear fractures are occurring. Wind speed and direction
   is linked indirectly to instability.
8. Highly correlated means there is an indirect relationship between
   two elements in a system. This loosely coupled relationship means that
   a change to one element in the system may or may not result in a change
   to the other element in the system and/or the change may be difficult to
   predict or ascertain.
9. Generally speaking, resolving highly correlated
   data requires a thorough conceptual understanding of the systems and data
   involved in order to create a link between the systems, or to refine the data
   into a format relevant to the case at hand ( e.g., a report of wind speed
   and direction must be linked with a visual observation of wind-loaded snow ).
   This linkage can only formed if the observer understands the concepts of,
   and relationships between, distributional data ( wind speed and direction )
   and singular data ( the case at hand, i.e. the visual observation of wind-loaded
   snow ). Even if wind-loaded snow is observed, it may be far away and still
   irrelevant to the case at hand.
10. Yes. Priority is given to Class I observations because this type of
    data reveals positive information ( highly prized ) about instability. Class II
    data only reveals the potential for instability and Class III data only
    reveals elements which might ( or might not ) contribute to instability.
11. In general, any datum which reveals instability is considered more important
    than any datum that contains little or no information about instability, regardless
    of its class.

VI. Scales In Space And Time

1. Avalanche forecasting operates at three primary spatial scales that
   refer to the geographic area of the forecast: synoptic scale, meso scale,
   and micro scale.
2. Avalanche forecasting operates along the temporal scale, including
   the distant past, recent past, the present, and the near future. Avalanche
   forecasting typically does not operate past the near future because of the
   chaotic nature of the data require ( i.e. the accuracy of long range
   weather forecasts is far from assured ).
3. Scale matching involves resolving the scale of information to the
   scale of the forecast. For example, one should not rely solely on a synoptic
   scale forecast for decision-making at the micro scale. The synoptic forecast
   is important but cannot take precedence over information relevant to the
   current situation. If one observes natural avalanches or cracking in the
   snow cover, one can assume high instability regardless of the information
   contained in the synoptic scale forecast. Fundamentally, scale matching is necessary
   because information found at one scale cannot be simply applied to
   another scale. Seeing cracks in the snow cover at one location in the mountains does not
   mean the snow is unstable for 100 miles in every direction.
   Quantity, rate, and duration of snowfall is another good example. Most
   quantitative precipitation forecasts are issued at the synoptic or meso
   scale. At the micro scale ( very local ) one may find far less or far
   more snow than indicated by a synoptic scale forecast.
4. Despite local signs of instability, a backcountry traveler might rely on
   a synoptic scale forecast and decide to ski an unstable slope. This could
   result in an avalanche. This is a good example of the link between the
   dynamic, evolutionary nature of avalanche forecasting and the use of
   singular and distributional information. The synoptic scale forecast
   constitutes distributional information; local signs of instability constitute
   singular information relevant to the case at hand.
5. The three primary spatial scales are as follows:
   
   • Synoptic. This is the largest scale: 1000 square kilometers.
   • Meso. This is the middle scale: 100 square kilometers.
   • Micro. This is the smallest scale: 1 square kilometer.
6. True.
7. As the scale decreases, difficulty of forecasting increases and the need
   for accurate information relevant to the case at hand increases as well.
8. Yes.
9. A now-cast is a forecast of instability for the present moment.
10. It is more difficult to forecast instability for next Thursday than for next Wednesday.
11. Weather is strongly linked to avalanche formation. The ability to
    successfully forecast avalanches is strongly influence by the essentially
    chaotic nature of weather.

VI. Decision-Making

1. The following is a basic list of steps used to issue an avalanche forecast:
   
   1. Data collection and integration.
   2. Analysis.
   3. Objective decision-making.
2. Formalizing the decision-making process prevents ( or reduces ) bias.
3. The spatial and temporal variability of the snowpack, in conjunction with
   incremental changes due to snow and weather and variations in human perception,
   creates the fundamental residual risk associated with avalanche forecasting.

Conclusions

1. Complex links between the elements of applied avalanche forecast
   make it difficult to conceive avalanche forecasting as a chain of events.
2. Terrain and climate are viewed as distributional information. In general,
   terrain and climate are included, implicitly, in most aspects of avalanche
   forecasting.

Biases

1. The search for supportive evidence is expressed as a willingness
   to gather facts that support the desired conclusion while disregarding
   facts that support an alternate, or undesired, conclusion. To prevent
   this bias, always search for information that reveals instability.
2. Inconsistency is expressed by applying different sets of
   decision-making criteria to similar situations. One might use the
   presence of existing ski tracks to justify the decision to descend
   a steep slope. In this case, the decision is based solely upon the
   existence of ski tracks, when without the presence of ski tracks
   one might use an entirely different set of criteria to evaluate
   instability.
3. Conservatism is expressed by failure to change one's mind when
   new information or evidence becomes available. This can affect
   evaluation of instability in either direction, and of course,
   this is linked directly to decision-making. Keep an open mind
   and use a formalized decision-making process to neutralize this bias.
4. Recency is expressed by allowing events from the most recent
   past to dominate decision-making at the expense of events in the
   less-recent past. Consider the current situation ( singular )
   and past situations ( distributional ) when making-decisions.
   This bias is very important when instability persists for a long
   time.
5. Frequency is expressed by allowing very frequent events to
   dominate decision making at the expense of less-frequent events.
   Consider the current situation ( singular )
   and past situations ( distributional ) when making-decisions.
6. Availability is expressed when decision-making is dominated
   by specific events easily recalled from memory at the expense of
   information relevant to the case at hand.
7. Illusory correlations is expressed a link is "seen" between
   data when no such link exists. Deductive reasoning is strongly
   affected by this bias.
8. Selective perception is expressed by viewing a problem in the
   context of one's own background and experience. Allow everyone
   to have input, especially people with different backgrounds.
9. Expert halo is expressed by allowing one person's expertise
   ( real or perceived ) to dominate decision-making. Everyone in
   the group ( skiers, forecasters ) should contribute to the decision.
10. Underestimating uncertainty ( denial ) is a method of coping
    with anxiety, especially when the outcome is time-pressured or
    may have a serious outcome. Consider distributional and singular
    information inside a formalized decision-making process to neutralize
    this bias.
11. Excessive optimism is expressed by denial. Seek the opinion of
    a disinterested third party to neutralize this bias.
12. Anchoring is expressed when initial information is given
    more weight in the forecasting process than new information. During
    a ski tour, signs of instability might not be present. However if
    signs of instability appear, it is possible to try and extrapolate
    to the best case scenario, i.e., instability is isolated in this
    location only. While this might be true, it is important to remember
    that "might" is the operational word.
13. A rule of thumb is expressed by a rule that greatly oversimplifies
    the problem. Consistency ( staticity ) in situation is required for a rule of thumb
    to work properly and avalanche forecasting considers a variety of
    very specific, and dynamic, situations. Using a rule of thumb
    almost guarantees that one will overlook important information
    and this will have a negative effect on the decision-making
    process.
14. Clients sometimes pressure guides to travel over terrain that
    is too dangerous. An inexperienced client should not be allowed
    to override the instability assessment of an experienced guide.
15. Social proof is expressed by seeing other people doing something
    without consequences and believing that one can do the same thing
    without consequences. Formalize the decision-making process.

Q & A

I have been hyperbusy with personal stuff, so thanks for your patience. Today, I'm going to answer a few questions that have been sent my way over the past few weeks.

( Promise a full post tomorrow or the next day-I've managed to read through most of the ISSW 2010 papers, and I've got a few additional remarks that I'd like to make about some recent conversations in which I have participated. )

Do avalanches originate in tree-covered areas?

Good question. Trees definitely alter the snowpack by anchoring snow, intercepting snowfall, intercepting radiation, and by depositing "bombs" and moisture that break up the snowpack.

1. According to The Avalanche Handbook, avalanches in tree covered areas are infrequent, but they do happen. If you travel in mountainous terrain during the winter, you can rely on very thick tree cover for safety only when there is no avalanche terrain anywhere above the trees.
2. Avalanches frequently initiate above tree-covered areas and flowing snow travels easily through the trees, even if the trees are thick. Have you ever noticed snow plastered on the uphill side of a tree? This is a good indicator of avalanche activity, and can also be used to determine the height of flowing snow. Remember that forest clearings may be especially dangerous because of instantaneous changes in snow conditions. This means that you can go from safe to unsafe in just a few steps.
3. Gladed areas are, for all intents and purposes, the same as open slopes. The consequences of taking a ride through the trees are severe. How severe? Think about what might happen if you have a high-velocity encounter with a tree. You can express such an encounter with the following formula: NOTFUN.
4. You may not be safer in forested areas, and if conditions are very poor, you might actually be less safe. As always, you must use the current terrain, weather, and snowpack to determine the likelihood of avalanche formation, and you must choose terrain appropriate for conditions.
5. According to researchers, people in North America are much more likely to suffer traumatic injuries during avalanches than their counterparts in Europe. Trees are definitely a contributory factor.
6. Don't forget about tree wells.

Other facts about trees and the snowpack.

1. Thick trees anchor the snowpack, which can prevent avalanche formation. On the other hand, trees often serve as trigger points or fracture points. It's a good idea to keep this in mind.
2. Trees intercept incoming shortwave radiation, which explains why you can find decent snow in the trees several days after a storm.
3. Trees intercept outgoing longwave radiation and reflect it back into the snow cover, which prevents heat loss. This is why surface hoar doesn't form readily beneath trees, and it's also why you're less likely to find near surface facets underneath the trees unless the temperatures are really really cold.
4. Trees drop bombs and liquid water onto the snowpack. Large snow bombs break up slabs, and liquid water turns the snowpack into solid concrete when it freezes.

How are buried facets formed?

This is a bit more complicated.

1. Facets can form inside the snowpack when the air is much colder than the ground on which the snow sits. The strong temperature difference means that water vapour moves quickly toward the snow surface, and a constant replenishment of water vapour means that crystals can grow rapidly. Rapid growth produces angular crystals.
2. Facets can form inside the snowpack itself when a crust creates a vapour barrier that traps moisture. Over time, with vapour supply and the right temperature gradient, fast crystal growth occurs. Once again, rapid growth produces angular crystals.
3. Facets can also form at the snow surface. This happens with very cold ambient air temperatures, or when the snow surface becomes intensely cool from longwave radiation loss.
4. Radiation recrystallisation can also produce facets. This happens when sunlight strikes very cold snow, and usually happens on south faces at at very high elevations.
5. Finally, facets can form when cold, dry snow falls on wet snow. The wet snow contains heat that sets up a strong temperature difference when it comes into contact with cold, dry snow. Again, as with above, the strong temperature gradient moves moisture rapidly, and constant replenishment of water vapour means that crystals can grow rapidly.

The Life of a Snowflake

Time is a wheel in constant motion always, moving us along—Lee Ann Womack

Double Post Wednesday. I'm going to be busy for the next few weeks, so I'm posting twice today. The first post, below, is a brief essay on the importance of understanding snow metamorphism- from crystal formation in the atmosphere, through deposition on the ground, and inside the snowpack itself. The second post is a snow metamorphism exam based on Chapter 3 of The Avalanche Handbook. It's ridiculous, but some people will enjoy it.

***

NOTE: This is the third post that will address the general question of Why Is It So Complicated? This time we're going to talk about snow metamorphism. I don't really know how to teach anyone about snow metamorphism, but hopefully this post will provide a basic understanding of why snow metamorphism is important and how it can be applied in the field. In my own experience, I literally cannot imagine making safe decisions without having significant knowledge of snow metamorphism, but this statement applies to me and me alone. As Ed LaChapelle said, there are many ways to forecast avalanches.

If you read this blog often, you may notice that I try to describe things in very literal terms. On first read, this post is going to seem like a departure, because I do use some highly subjective language. Please keep in mind that I do not approach backcountry avalanche forecasting from a mystical perspective; I actively observe the environment—right down to the way the air feels on my nose after a few rapid breaths*—and I draw my observations from the science, not the psychic.

( *A very chilled nose after three rapid breaths means extra caution delivers good skiing. )

Polymorphism

The term polymorphism is the ancient Greek word for many forms and it very neatly describes the heart of the complexity and uncertainty that many people experience when they think about snow crystals. But you and I, we aren't so different from snowflakes, because over our lives, we also react to the dynamic conditions around us, and we too change as a result. Sometimes these changes are for the better, and sometimes they're for the worse.

Ask yourself the following question: Am I the same person I was 5 years ago?

Of course not.

So the simple fact of the matter is that, as with people, snowflakes change with the passage of time. The principles of snow metamorphism are incredibly useful, and in this post I refer to snow metamorphism in the holistic sense: changes to snow crystals in the clouds, changes to snow crystals on the ground, and changes to snow crystals in the snowpack.

The Life of A Snowflake
Snowflakes are born in clouds of supercooled water vapour. Both the temperature and the amount of moisture available for crystal formation vary over time and space in the atmosphere, which means that the neither the temperature, nor the amount of moisture, are consistent. This is responsible for variations in crystal form as the snow falls, and variations in crystal form are very important if you're a backcountry skier.

But let's get back to our snow storm. As we all know, eventually gravity pulls the snowflakes to Earth, where they form a layer. On the ground, the amount of water vapour and the temperature are different than in the clouds, so the snowflakes begin to change. The first observable changes are the loss of branches as the fine details of the snow flake melt. Soon thereafter, as the crystal size decreases, the weight of the snowpack produces overburden pressure that pushes the snowflakes into each other, effectively crushing them and further reducing the pore space. These changes happen in a relatively short amount of time, from a few hours to a few days.

Over the longer term, the temperature gradient determines how quickly water vapour moves through the snowpack, which determines whether or not the snowpack becomes stronger or weaker. Thick, deep snowpacks are strong because moisture transport is slower and weaknesses are crushed and rounded out of existence. Thin snowpacks are weak because moisture transport is fast, which leads to rapid crystal growth and angular shapes with cavernous pore spaces and fewer bonds. Furthermore, cold temperatures preserve existing weaknesses such as crusts and buried surface hoar.

What I Think About
Okay, I've rattled on and on about the delights of snow metamorphism, but what are the practical concerns? Well, having a strong working knowledge of snow metamorphism leads me straight to the following questions:

• Are there instabilities in the new snow itself? ( Timeframe: 24-72 hours )
• Are there instabilities in the bond between the new snow and the old snow? ( Timeframe: Up to 7 days )
• Are there older instabilities and how will they react to loading by snow or skiers? ( Timeframe: Entire winter )

At first glance, this list probably seems quite thin, but continue reading if you'd like to see how a strong working knowledge of snow metamorphism allows me to integrate some very useful details into these broad questions. The first concern is, of course, given the questions above, how can you identify snowpack with dangerous characteristics?

Applying The Principles Of Snow Metamorphism In The Field
If you know what to look for, you can observe these conditions in the snowpack. Recently, I was out on a ski tour the morning after a significant storm. In the Cascades, this generally means that it's time to watch your ass, as snow often arrives in large amounts, and with significant wind. Consider the following list of observations from multiple locations. These observations were based on, or related to, a strong working knowledge of snow metamorphism.

• Constant presence of decomposing crystals at the snow surface.
• Uniform crystal density in the new snow.
• Uniform increase in hardness with depth.
• Loss of branches on new snow crystals.
• The crystals at the bottom of the snow had fewer branches than the crystals at the top.
• The pore space at the bottom was smaller than the pore space at the top.
• The bond between the old snow and the new snow was bomber.
• Zero slab avalanches.
• Very little sluffing.
• Few drift lines in the alpine.
• Good snow coverage on trees regardless of orientation.

Going Behind The Scenes
Instabilities in new snow are often represented by soft slab avalanches that form in the new snow itself, or by avalanches that form when dense wind slab overlies softer snow below. An understanding of snow metamorphism can help you learn what to look for when you need to determine whether either type of avalanche is likely.

In a perfect blanket of new snow, you should observe uniform increases in hardness with depth. This is often referred to as right side up snow. However, it's not the only possibility. In addition to upside down snow, any new layer of snow could contain internal weaknesses. These usually take the form of a band of heavier snow crystals overlying a band of lighter snow crystals inside the layer of new snow. Suffice it to say, although the new snow might be mostly right side up, it needs to be completely right side up.

Weaknesses of this type form because the atmosphere in which snow crystals form is inconsistent with respect to temperature and the amount of water vapour. This means that the mass and shape of snow crystals can vary. A storm may at first lay down a few centimetres of of light crystals, followed by a few centimetres of heavy crystals, followed by a few more centimetres of light crystals.This creates a complex layering that is highly suitable for avalanche formation; even though the snowpack is mostly right side up.

Wind slab is upside down snow, but it forms for different reasons. Snow crystals shatter when moved by the wind, and they form a fine dust-like mist that accumulates on lower density snow in sheltered areas. Over the course of a few hours, this fine mist turns into a thick layer of tiny crystals. The tiny grains have a high number of bonds per unit volume, and this enables them to knit together very rapidly. However, the new snow below may not be able to support the weight of the slab, and avalanches form quite easily when you crush the weaker snow below by applying a dynamic load to the wind slab. In an instant you have something on top of nothing, and an instant later you have an avalanche.

For older weaknesses, there are two concerns over the long term: favourable metamorphism that comes with depth and relative heat, and overburden pressure that slowly crushes weaknesses and fills in the pore spaces. Obviously, without a working knowledge of snow metamorphism, it's going to be pretty hard to know what to look for. I'm not comfortable writing much more about older weaknesses, because research also shows that they're not very manageable. Therefore, unless you have professional-grade knowledge, you should avoid trying to diagnose these problems.

This might seem complicated, but it's much easier to understand if you have a decent working knowledge of snow metamorphism across various scales of space and time. On the day of our trip, we had deep, stable snow that was well-bonded to the old snow below. I was very comfortable skiing in steep avalanche terrain without constantly feeling the need to look over my shoulder.

Conclusion
Much of the information used during my recent trip was pulled directly from the principles of snow metamorphism. I sometimes hear people say that introductory avalanche education should focus less on snow metamorphism and more on decision-making. This makes me scratch my head in confusion.

How can you make critical decisions about snow when you know almost nothing about it? Continuous avoidance of avalanche terrain simply isn't compatible with realistic human behaviour, and you can't travel safely in avalanche terrain if you don't understand snow.

Perhaps this winter I will turn my brain toward developing a realistic, usable framework for understanding snow metamorphism. Of course, it might not be possible to develop this framework, in which case, I'll point you straight at This Little Monster.

Snow Metamorphism Exam

255 questions from chapter 3 of The Avalanche Handbook. Questions start with green headings and answers start with red headings. I'm not sure how long it will take to complete this exam, but I can guarantee that you will gain professional-level knowledge about snow metamorphism if you master 90% of this material.

Yes, I am fully aware that this exam is ridiculous, but it was a lot of work, so have fun.

Capsule

This chapter discusses snow formation from cloud to ground, including in-depth information on snow metamorphism and its links to avalanche formation.

Snow Crystal Formation And Growth in The Atmosphere

1. Variations in snow crystal type are responsible for some avalanches. True or False?
2. Explain this relative to potential instability in new snow and old snow.
3. Clouds are composed of what elements?
4. Inside an air mass, what specific process leads to cloud formation?
5. List two types of particles that serve as condensation nuclei?
6. What is the typical diameter of such a particle?
7. Condensation nuclei are rare. That's why you don't see clouds everywhere. True or False?
8. When does formation of ice crystals become possible?
9. Ice crystals always form when the temperature reaches 0 degrees Celsius. True or False?
10. What is the typical size of a water droplet in a cloud?
11. What is the typical concentration of water droplets in a cloud?
12. What two elements are required for ice crystal formation above -40 degrees Celsius?
13. Freezing always takes place at constant temperatures in clouds. True or False? Explain.
14. At what temperature will water droplets freeze by themselves?
15. What two processes determine subsequent growth once an ice crystal has formed?
16. Describe the initial process of crystal growth.
17. Describe the secondary process of crystal growth.
18. Branches form from which mechanism?
19. Branches are destroyed by which mechanism?
20. What process creates graupel?
21. What process forms hail?
22. Describe a novel use for graupel ( Be creative. Invent something. ).
23. What is the most important variable with respect to crystal form?
24. What are the two primary crystallographic axes?
25. How many intrinsic axes are found along the base axis?
26. Describe the symmetry of the basal plane.
27. Along which axis does heat flow most efficiently?
28. Platelike crystals form from growth along which axis?
29. Needlelike crystals form from growth along which axis?
30. Why are crystals six-sided?
31. Is rate of growth a strong factor in final crystal shape?
32. At low excess vapor density, what shape is produced regardless of temperature?
33. What vapor quantity condition is implied by a complex crystal?
34. Describe vapor and temperature regimes.
35. Crystals that fall through a cold atmosphere are larger. True or False?
36. Name one crystal type that often serves as a future sliding layer?
37. Changes between crystal type or riming can result in poor bonding between layers. True or False?
38. ________ ________ are expected at low vapor density; ________ ________ are expected at higher vapor density.
39. Explain the concept outlined by the previous sentence.
40. Define the terms behind the acronym "ACMG"

Classification Of Newly Fallen Snow Crystals

1. How many levels of classification are typically used to describe new snow?
2. Describe each level.
3. How many crystal classifications are used in each?
4. Describe the typical crystal composition of new snow in simple terms ( not by specific crystal type ).
5. What effect does this have on avalanche forecasting?
6. What crystal type is of particular importance? Why?
7. Describe the correct process for crystal identification at the snow surface.
8. How do you measure and record the size of snow crystals in the field?
9. List the levels used for crystal grain size classification, including name and size.

Surface Hoar: Formation And Growth Conditions

1. Provide the common definition for surface hoar.
2. Under what condition does surface hoar form? Be very specific.
3. What is the result of this condition? Be very specific.
4. Provides a visual description of surface hoar.
5. What are the two conditions for continued growth of surface hoar?
6. Surface hoar usually forms on ________ ________ ________ with ________ or ________ ________ conditions in the ________ ________ of ________.
7. Slight air movement destroys surface hoar. True or False?
8. Describe the rate of air motion necessary for vapor replenishment.
9. How would an observer regard these conditions?
10. What happens if air motion is turbulent?
11. What usually creates the temperature gradient necessary for surface hoar formation?
12. ________ % humidity is usually required for rapid growth.
13. Below the % of humidity specified above, surface hoar growth is not possible. True or False?
14. Describe one scenario during which formation of surface hoar might be expected.
15. Clouds, especially high, thin clouds, enhance surface hoar formation by contributing moisture. True or False?
16. If true, explain. If false, explain.
17. If clouds are present, what factor determines their effect on surface hoar formation?
18. Describe a terrain feature that might inhibit surface hoar formation.
19. Why does this terrain feature inhibit surface hoar formation? Be very specific.
20. Surface hoar forms readily under forest because forest has a sheltering effect. True or False?
21. If true, explain. If false, explain.
22. Mountain guides often call logged clear cuts "lunch counters". True or False?
23. If true, explain. If false, explain.
24. Avalanches are rare in clear cuts. True of False?
25. If true, explain. If false, explain.
26. In what snow climate is surface hoar found? Be very specific.
27. Once formed, surface hoar is extremely strong. This is why it persists for such long periods. True or False?
28. Describe three conditions that might destroy surface hoar.
29. Surface hoar is sometimes a more significant problem at lower elevations. True or False?
30. If true, explain. If false, explain.
31. In addition to being pretty, surface hoar is good at producing ________ ________ ________.
32. What is the term used to describe the mechanical strength of surface hoar?
33. What does this term mean?
34. Why is this important?
35. What provides energy to drive a fracture forward when surface hoar is disturbed?
36. It is only safe to travel across buried surface hoar on flat terrain. True or False?
37. If true, explain. If false, explain.
38. How might surface hoar gain strength?
39. What layer variable determines how long surface hoar remains unstable?
40. What is the range of size for surface hoar crystals?
41. Surface hoar is often described as a ________ ________. Or ________ ________ ________ ________.
42. Unlike facets, surface hoar is easily destroyed, and therefore not responsible for major avalanches. True or False?
43. Wild-harvested, Selkirk surface hoar is highly prized as both a recipe ingredient and ice cream garnish at fancy restaurants in Japan. True or False?

Snowpack Temperatures And Temperature Gradients

1. What serves as the upper and lower boundaries for winter snowpack?
2. What is the temperature of the lower boundary and why?
3. What is the temperature of the upper boundary and why?
4. Which boundary is usually cooler?
5. Define diurnal fluctuation.
6. Define the two elements of a temperature gradient in terms of a bipartite vector.
7. How is the temperature gradient expressed?
8. What is the term for a snowpack that lacks a temperature gradient?
9. What can you assume about this snowpack?
10. When does this occur?
11. Describe, in very simple terms, the quality of the temperature gradient in a maritime climate.
12. Why is this the case?
13. Describe, in very simple terms, the quality of the temperature gradient in a continental climate.
14. Why is this the case?
15. What explains the very general difference in character of avalanching in these climates?
16. As shown above, crystals are dependent on climate, not physical processes. True or False?
17. Certain crystal types are not found in some snow climates. True or False?

Snowpack Temperatures And Temperature Gradients

1. Once deposited on the ground, how many minutes must pass before snow crystals begin to change form?
2. Why do these initial changes cause direct-action, loose-snow avalanches?
3. Why do crystals change form?
4. What is the range of typical values for supersaturation in the atmosphere?
5. What is the range of typical values for supersaturation in the snowpack?
6. New snow crystals are highly stable. True or False?
7. What ratio and quantity describes unstable crystals?
8. In very general terms without regard to specific crystal type, which crystals are most stable?
9. In very general terms without regard to specific crystal type, which crystals are least stable?
10. What shape has the minimum surface area to volume?
11. What effect might crystals of this shape have on stability of crystal shape?
12. What causes the disappearance of intricate crystal branches?
13. Vapor pressure over a ________ surface is higher than vapor pressure over a ________ surface.
14. Therefore, what crystal shape quality promotes sublimation?
15. Where does this water vapor go?
16. What is the implication of the production of water vapor via sublimation?
17. Saturation vapor pressure increases by what percent across what temperature range?
18. What is the implication of this?
19. List the three factors that influence metamorphism in dry snow.
20. Define each factor.
21. Where is the temperature gradient usually highest?
22. This region is defined as the ________ ________ ________ ________ ________.
23. What are the two key factors that determine rate of metamorphism for dry snow?
24. What is the initial result of branch disappearance with respect to crystal size?
25. What is the name for this process. Be very specific.
26. What happens next? Why?
27. ________ particles grow at the expense of ________ particles.
28. Average particle size ________ when a mixture of sizes is present.

Dry Snow Metamorphism In The Seasonal Snow Cover

1. Why are the variety of crystal forms limited inside the snowpack?
2. The term metamorphism includes changes to form induced by these two factors.
3. What snowpack-related force rearranges grains in the snowpack?
4. Relative to crystal configuration in the snowpack, what is the result of this rearrangement process?
5. How might this affect both stability and instability in the short and long term?
6. What process dominates shape change in glaciers or firn snow?
7. What is the primary difference between crystal formation in the atmosphere -vs- in the snowpack?
8. How does the temperature gradient influence vapor diffusion? Be very specific.
9. What is the general result with respect to motion of water vapor?
10. Specifically, how does mass transport occur under this effect?
11. What determines crystal forms that develop under this recrystallization process?
12. With respect to water vapor, rate of motion increases as these three factors increase.

Crystal Forms In Dry, Seasonal Alpine Snow

1. Growth rate and crystal form are more dependent on pore size than temperature gradient. True or False?
2. If true, explain. If false, explain.
3. High temperatures, large temperature gradients, and large pore spaces result in what growth rate?
4. Low temperatures, small temperature gradients, and tiny pore spaces result in what growth rate?
5. What is the critical temperature gradient required to produce faceted crystals?
6. How do you measure a temperature gradient?
7. Faceted forms and highly angular snowflakes develop because of similarities between vapor saturation conditions in the atmosphere and snowpack. True or False?
8. Why does depth hoar only form near the ground? Be very specific.
9. Why do facets form slowly in very cold snow? Be very specific.
10. At high growth rates, what crystal forms are expected?
11. At low growth rates, what crystal forms are expected?
12. What affect might growth rate have on snowpack instability?
13. List three examples of crystals types produced at high growth rates.
14. High growth rate crystals form preferentially in what type of snow climate?
15. Connect the number of avalanche fatalities in Colorado with its snow climate.
16. Which are the top five states with respect to avalanche fatalities?
17. Large pore spaces present favorable conditions for what type of crystal?
18. What pore space quality inhibits development of facets?
19. Describe a method used to decrease pore space in depth hoar and when this method must be implemented.
20. Depth hoar is always weak. True or False?
21. What is near-surface faceted snow?
22. What are the persistent forms? Explain each type.
23. What are mixed forms?
24. Crystals developing under the slowest growth rates are referred to as ________.
25. Crystals developing under the highest growth rates are referred to as ________.
26. Draw the symbol for "new snow or precipitation particles".
27. Draw the symbol for "decomposing and fragmented precipitation particles".
28. Draw the symbol for "rounded grains ( monocrystals )".
29. Draw the symbol for "faceted crystals".
30. Draw the symbol for "cup-shaped crystals; depth hoar".
31. Draw the symbol for "wet grains".
32. Draw the symbol for "feathery crystals".
33. Draw the symbol for "ice masses".
34. Draw the symbol for "surface deposits and crusts".
35. Why was the term "equitemperature metamorphism" discarded?
36. Why was the term "temperature gradient metamorphism" discarded?
37. What is the name for the crystal type that constitutes the largest size found in the snowpack?
38. Why are these crystals the largest?

Growth Of Crystals Around Crusts In Dry Snow

1. How does a crust influence crystal formation?
2. With respect to crusts, what is the most important feature for avalanche formation?
3. Why do facets sometimes grow directly beneath a crust?
4. What leads to dry/wet faceting?

Bond Formation In Dry Alpine Snow

1. Formation of bonds is also referred to as ________.
2. How does bond formation occur?
3. Where do bonds form?
4. What is found at the boundary between two crystals?
5. Describe the perspective from which experimental work on bond formation in dry snow has been conducted.
6. What is the final angle of the dihedral?
7. Stress along the grain boundary is constant. True or False?
8. If true, explain. If false, explain.
9. Describe the process of bond formation relative to rate of bond formation over time.
10. Discuss how differences in crystal size affect stability with respect to bond formation.
11. Thermodynamic processes occur ________ at ________ temperatures.
12. What is the temperature threshold for persistence of instability in new snow?
13. In theory, what exists at the surface of crystals? What happens to this theoretical region as temperature increases?
14. When the temperature gradient is high, mass transport is ________.
15. Discuss the spatial characteristics of vapor deposition under a high temperature gradient.
16. If avalanches released easily on depth hoar, what conclusion could be drawn about travel in continental climates?
17. What conclusion is reached instead?
18. When snow falls at high temperatures, rapid bond formation decreases what?
19. Discuss bonds / unit volume with respect to grain size.
20. What is necessary for bond formation between adjacent layers of snow?
21. How does the degree of riming effect bond formation?
22. Broken crystals are usually small. What effect does this have on bond formation?
23. List the integrated elements of bond formation and layer strength for dry snow.
24. Fractures originate at what scale relative to the size of an individual bond?
25. Why is this important?
26. What is the most important temperature effect on dry slab-formation relative to avalanche forecasting?
27. Discuss the nature of bonding and strength increases for the persistent forms.
28. Mismatches in crystal type enhance bond formation because opposites attract. True or False?
29. Where do persistent forms originate? Name the exception.
30. What do studies of avalanche fracture lines suggest about layering and bonding?
31. What information about layering and bonding can one derive from instability tests?

Persistent And Non-Persistent Weak-Layer Forms

1. Who coined the term "persistent forms"?
2. What are the characteristics of the persistent forms?
3. What are the characteristics of the non-persistent forms?
4. Discuss human perception with respect to persistent forms.
5. Discuss human perception with respect to non-persistent forms.
6. When do non-persistent forms originate?

Metamorphism Of Wet Snow

1. What happens to heat flow and metamorphism in wet snow?
2. Wet snow can consist of what three materials?
3. Discuss the relationship between melting point and particle size.

Snow With High Water Content

1. Discuss particle separation in wet snow. Include the percentage of water content by bulk volume required for complete grain separation.
2. What drives metamorphism in water-saturated snow?
3. In theory, when does metamorphism stop?
4. Since differences in melting temperature due to curvature is very small in wet snow, why does metamorphism occur rapidly?
5. Define "dry snow".
6. Define "moist snow".
7. Define "wet snow".
8. Define "very wet" snow.
9. Define "slush".
10. What is a pendular regime?
11. What is a funicular regime?

Snow With Low Water Content

1. At what level of water content does grain growth occur through vapor flux?
2. Relative to the pore space, what develops as water content in wet snow decreases?
3. What is the result of this?
4. What is the distinguishing visual feature of moist snow?
5. What is responsible for this occurence?
6. How can you differentiate between wet and dry snow?
7. What is the most accurate method of measuring the water content of snow?
8. As water content increases, what can you expect about grain growth?

Classification Of Wet Snow

1. Does the grain classification of faceted snow change when it becomes wet? Explain.

Bond Melting And Formation In Wet Snow

1. What has the highest heat conductivity of all common substances?
2. Describe what happens to the melting point of grains when grains touch in water saturated snow.
3. Describe the process of melt-freeze metamorphism.
4. What is the colloquial term for snow crystals created by melt-freeze metamorphism?
5. How do melt-freeze crusts contribute to avalanche formation?

Snow Crystal Formation And Growth in The Atmosphere

1. True
2. Variations in crystal size and type can lead to poor between layers of new snow. This causes new snow instability.
   Later, these variations can result in grain size mismatch and poor bonding between layers of old snow. This
   causes deep instability.
3. Water droplets
4. Condensation of water molecules onto condensation nuclei.
5. Salt, dust, soil, spores.
6. 1 micrometer.
7. False. Condensation nuclei are always in abundant supply.
8. At 0 degrees Celsius.
9. False
10. 20 micrometers.
11. Several hundred per cubic centimeter.
12. Freezing nuclei and and temperatures below 0 degrees Celsius.
13. False. Water droplets can remain in liquid phase ( supercooled ) at temperatures below 0 degrees Celsius.
14. -40 degrees Celsius.
15. Vapor pressure gradients and riming
16. Water molecules are deposited directly on tiny ice crystals by vapor pressure gradients in the cloud.
17. Riming occurs as the enlarged crystal falls through the atmosphere and collides with water droplets.
18. Vapor deposition.
19. Riming
20. Riming, long growth period, multiple passes through clouds on thermal updrafts.
21. Multiple passes through freeze-thaw cycles in clouds.
22. Graupel makes a festive decoration for mountain martinis or other cold beverages.
23. Temperature
24. A and C or planar and vertical.
25. Three. Separated by 120 degrees.
26. Hexagonal
27. Along the C ( vertical ) axis.
28. A
29. C
30. Hexagonal symmetry of the A axis.
31. Yes
32. Columns
33. High quantity of water vapor or high supersaturation.
34. Vapor regime is a specific area with a specific level of saturation. A temperature regime is a specific area at a specific temperature. Clouds often have multiple vapor and temperature regimes.
35. False
36. Stellars
37. True
38. Rounded forms are expected at low vapor density; edges and corners are expected at higher vapor density.
39. Slow growth, from low vapor density, produces rounded forms. Fast growth, from high vapor density, produces angular forms.
40. Attractive Canadian Men on Glaciers.

Classification Of Newly Fallen Snow Crystals

1. Two
2. The first level uses the "+" symbol to describe all new precipitation in a single category. The second level uses five crystal types, and three irregular crystal types, to sort precipitation into specific forms.
3. 1, 8
4. Mixed, or a variety of types are mixed together.
5. This can complicate decision-making.
6. Stellars - because they're flat and often form sliding layers.
7. Use a loupe to determine the predominant crystal type in a sample.
8. Place crystals on a millimeter grid and provide a range of sizes, i.e. 0.2 to 0.5 millimeters.
9. Very Fine 0.2mm, Fine 0.2-0.5mm, Medium 0.5-1mm, Coarse 1-2mm, Very Coarse 2-5mm, Extreme >5mm.

Surface Hoar: Formation And Growth Conditions

1. Frozen dew
2. When the water vapor pressure of air exceeds the water vapor pressure of ice crystals on the snow surface.
3. Sublimation of water directly onto the snow surface.
4. Large, glittering, feathery crystals.
5. Sufficient water vapor and temperature gradient at the snow surface.
6. Surface hoar usually forms on clear, cold nights with calm or nearly calm conditions in the lowest meter of air.
7. False
8. A few centimeters per second.
9. As calm or similar to air motion in an enclosed room.
10. Destroys the temperature gradient.
11. Long wave radiation loss.
12. 70 % humidity is usually required for rapid growth.
13. False
14. If a cold front passes after an overcast day.
15. False
16. Clouds can destroy the temperature gradient by preventing loss of long wave radiation.
17. The temperature difference between the cloud and the snow surface.
18. Concavity
19. Long wave radiation is reflected back onto nearby snow ( parabolic / anti-diffusion effects ), destroying the temperature gradient.
20. False
21. Forest cover inhibits loss of long wave radiation, which prevents formation of temperature gradient.
22. False
23. Mountain guides often call logged clear cuts "surface hoar farms".
24. False
25. Surface hoar formation and clear ground suitable for loading result in avalanches that release in clear cuts.
26. Any climates, provided conditions necessary for formation are met.
27. False
28. Wind, sun, rain.
29. True
30. Often, surface hoar is easily destroyed by high winds and harsh conditions found at higher elevations.
31. In addition to being pretty, surface hoar is good at producing propagating shear fractures.
32. Anisotropic
33. Weaker in shear than compression.
34. When surface hoar is loaded, force is transferred from compression to shear.
35. Collapse
36. False
37. Even on flat terrain, movement over buried surface hoar can result in shear fractures that travel uphill to release an avalanche above the traveler.
38. Bond formation with adjacent layers.
39. Thickness
40. 1 millimeter to several centimeters.
41. Surface hoar is often described as a persistent form.Or pain in the ass.
42. False. Surface hoar is easily destroyed before burial but once buried persists for a long time because its compressive strength means it resists strength by overburden.
43. True or false are acceptable answers.

Snowpack Temperatures And Temperature Gradients

1. Lower boundary = ground. Upper boundary = air.
2. 0 degrees because of stored heat from summer ( most important ) and geothermal heat from the Earth's core.
3. Variable. The air temperature is set by the atmospheric conditions.
4. Upper
5. Daytime warming, nighttime cooling.
6. A vector having both magnitude and direction.
7. In degrees Celsius per meter.
8. Isothermal
9. It contains water.
10. Spring
11. Weak
12. Predominantly warm temperatures and deep snowpack.
13. Strong
14. Predominantly cold temperatures and shallow snowpack.
15. The crystal forms produced are very different.
16. False
17. False

Snowpack Temperatures And Temperature Gradients

1. Zero
2. Loss of branches causes loss of cohesion through reduction in static friction.
3. Differences in supersaturation/temperature between the snowpack and the clouds.
4. Tens of percents
5. 1%
6. False
7. Large ratio between surface area and volume, i.e. dendrites -vs- spherical crystals such as graupel.
8. Round forms.
9. Angular forms.
10. Sphere
11. Spherical crystals retain their original form for a long time.
12. Vapor pressure over sharply curved branches is very high.
13. Vapor pressure over a convex surface is higher than vapor pressure over a concave surface.
14. Sharpness, Angularity, Edges, Creases
15. Into the surrounding air.
16. Water vapor is available for additional crystal development.
17. 300% between -15C and 0C.
18. This is the primary factor in metamorphism, rather than curvature effects.
19. Temperature gradient, grain curvature, overburden pressure.
20. Definition of each factor:
    
    • Temperature Gradient. Difference in temperature between snow at depth and surface of snow.
    • Grain curvature. The curvature of each grain in terms of convexity or concavity.
    • Overburden Pressure. The effect of the weight of snow above rearranges grains and produces contact points for bond formation.
21. Surface regions of the snowpack.
22. This region is defined as the top few tens of centimeters.
23. Temperature of snow and the temperature gradient.
24. Decrease in crystal size.
25. Destructive metamorphism.
26. Destructive metamorphism supplies water vapor, which in the presence of a temperature gradient moves through the snowpack and provides a means for ongoing changes to crystal form.
27. Larger particles grow at the expense of smaller particles.
28. Average particle size increases when a mixture of sizes is present.

Dry Snow Metamorphism In The Seasonal Snow Cover

1. Crystals are insulated by neighbors and physical conditions are slow to change.
2. Temperature and overburden pressure.
3. Overburden pressure
4. Pore space is decreased, crystals touch each other and form bonds.
5. Affect On Instability- This is is how slabs are formed. In the short term, this may result in enough cohesion for slab formation and release if a weak layer/interface is present. Affect On Stability- This process usually increases the hardness ( and therefore strength ) of the snowpack.
6. Overburden pressure
7. The amount of supersaturation in the air surrounding the crystals.
8. Warmer air holds more water vapor than colder air. Therefore water vapor pressure is higher at the bottom of the snowpack. Water vapor moves up through the snowpack in a hand-to-hand process.
9. Water vapor moves up through the pore space.
10. Water molecules move from the top of one crystal to the bottom of the crystal above.
11. Rate of motion
12. Temperature gradient, temperature, and pore space.

Crystal Forms In Dry, Seasonal Alpine Snow

1. False
2. While all both factors are important, temperature gradient is more important than available pore space ( second order effect ).
3. High
4. Low
5. 10 degrees Celsius / meter
6. Measure temperature at bottom of snowpack and air temperature above. Or measure temperature of layers.
7. True
8. Temperatures are high and a lot of water vapor is available for fast crystal growth.
9. Temperatures are low and water vapor is in short supply. This means slow crystal growth. High supersaturation and high temperatures are required for fast crystal growth.
10. Facets
11. Rounds
12. Faceted crystals are weak. Therefore a high growth rate produces crystals that foster/increase instability.
13. Surface hoar, depth hoar, facets.
14. Continental
15. Much of the Colorado snowpack is composed primarily of weak forms such as facets, depth hoar, and surface hoar because of high temperature gradients created by cold surface temperatures.
16. Colorado, Alaska, Washington, Utah, Montana ( CAWUM )
17. Facets
18. Small pore spaces, tightly packed crystals.
19. Bootpacking during the early season.
20. False
21. Facets produced near the top of the snowpack by temperature gradients, radiation recrystallization, crust influence, or dry/wet snowfall mixes.
22. The persistent forms are surface hoar, facets, depth hoar, and combinations of these with crusts.
    
    • Surface hoar. Feathery crystals produced by high humidity and long wave radiation cooling that creates a large temperature gradient at the snow surface.
    • Facets. Angular crystals produced by high temperature gradients.
    • Depth Hoar. Angular, cup-shaped crystals produced at the bottom of the snow by high temperatures and larger quantities of water vapor.
    • Crusts. Crusts are a persistent form once buried. You can find combinations of persistent crystal forms with crusts such as facets above/below a crust, or surface hoar above a crust.
23. Crystals with rounded and angular elements, usually transitions between round-to-facet or facet-to-round. These transition processes are called "faceting" or "rounding".
24. Crystals developing under the slowest growth rates are referred to as rounds.
25. Crystals developing under the highest growth rates are referred to as facets.
26. +
27. / ( or this symbol with a small break in the line )
28. o ( but it should be filled in )
29. [] ( should be a hollow square )
30. /\ ( upside down "V" )
31. o ( hollow circle )
32. \/ ( right side up "V" )
33. - ( thick, elongated dash )
34. \/ ( with a curved line through the top, like an upside down "A".)
35. Equiptemperature implies all snow is at the same temperature which is rare in alpine snow.
36. All metamorphism happens under a temperature gradient of some magnitude. With respect to crystal shape this term is not specific enough since it basically refers to all crystals.
37. Depth hoar
38. They have been growing the longest, under warm temperatures and higher supersaturation than crystals elsewhere in the snowpack.

Growth Of Crystals Around Crusts In Dry Snow

1. Provides a barrier for vapor transport.
2. Weak bonding of snow above or below the crust.
3. Vapor transport is prevented, which provides a relatively high level of supersaturation for rapid crystal growth.
4. Dry on wet snowfall combinations involve "dry" snow falling on "wet" snow. Latent heat in the water fosters a temperature gradient.

Bond Formation In Dry Alpine Snow

1. Formation of bonds is also referred to as sintering.
2. Diffusion of water vapor through pore space and molecular motion at grain boundaries.
3. At grain boundaries where crystals touch.
4. Grain boundary groove.
5. Generally from the perspective of ice spheres with a boundary where the spheres touch.
6. 145 degrees
7. False
8. Highest stress is found on the interior of the grain boundary groove.
9. Bond formation is initially quite fast, slowing gradually as time passes.
10. Differences in crystal size ( mismatch ) result in poor bond formation.
11. Thermodynamic processes occur faster at higher temperatures. Thermodynamic processes occur more slowly at lower temperatures.
12. -5 degrees Celsius
13. A mobile, liquid-like layer that thickens as temperature increases.
14. When the temperature gradient is high, mass transport is rapid.
15. Vapor molecules are not longer preferentially deposited at necks and growth occurs on sides and corners of crystals.
16. Travel in continental climates would be extremely dangerous.
17. Avalanches are not easily released on depth hoar because of its depth below the surface.
18. Instability
19. Large grains have fewer bonds per unit volume; smaller grains have more bonds per unit volume because of tighter packing.
20. Similar geometry / crystal grain type/size.
21. Differences in degree of riming can inhibit bond formation.
22. These crystals pack very tightly and bond very well. This is how slabs form.
23. List of integrated elements:
    
    • Temperature
    • Temperature gradient
    • Applied load
    • Pore-space configuration
    • Crystal type/size
    • Interface geometry
24. About 100 times individual bond size.
25. The individual bonds don't matter as much.
26. High temperature and load work together to increase fracture toughness.
27. Bonding and strength increase slowly for persistent forms because of large grain size, loose packing, and resistance to strength increases from overburden due to anisotropy.
28. False
29. In near surface snow. Depth hoar is the exception.
30. Weak bonding between layers may be more important than low strength in a weak layer.
31. Shear quality.

Persistent And Non-Persistent Weak-Layer Forms

1. Canadian researcher Bruce Jamieson.
2. Anisotropic: weaker in shear than compression, low-fracture toughness, may persistent for long periods of time.
3. Fracture toughness and bonding increase fairly rapidly due to overburden slab load and temperature. However instability may persist at temperatures below -5 degrees Celsius.
4. Human perception is poorer because of forgetfulness, spatial variability, or depth of burial.
5. Human perception is generally good because instabilities are near the surface.
6. During storms.

Metamorphism Of Wet Snow

1. Conditions change greatly.
2. Water, ice, and air.
3. Smaller particles have a lower melting point than larger particles.

Snow With High Water Content

1. At 15% water, ice particles may become completely separated from each other.
2. Heat flux through liquid water.
3. When all particles are the exact same size.
4. Heat flux through liquid water is extremely efficient.
5. Snow with 0% water content by volume.
6. Snow with < 3% water content by volume.
7. Snow with 3-8% water content by volume.
8. Snow with 8-15% water content by volume.
9. Snow with > 15% water content by volume.
10. This is another term for wet snow.
11. This is another term for very wet snow.

Snow With Low Water Content

1. 8%
2. Capillary pressure in the pore space.
3. Liquid water is forced out of the pore space, usually draining down.
4. Grain clustering that occurs as a result of surface tension.
5. Surface tension of water between grains.
6. Take its temperature, examine it with a lens, squeeze a handful.
7. Dielectric measuring device.
8. Grain growth increases because heat transfer through water is efficient.

Classification Of Wet Snow

1. No. The snow is still faceted because that is the actual grain type by morphological classification.

Bond Melting And Formation In Wet Snow

1. Water
2. The melting point decreases as area of contact increases.
3. During the day, snow melts, producing liquid water. At night, snow freezes. ( Diurnal temperature fluctuations. ) After several repetitions, the result is large grain sizes that lose most of their cohesion when wet.
4. Corn snow
5. A melt-freeze crust can serve as a future sliding layer if buried. A wet melt-freeze crust can produce wet/loose avalanches.