Storm Slabs
2-part: Are Storm Slabs generally Hard or Soft Slabs? What size do storm slabs rarely exceed?
Soft Slabs, due to their less cohesive/strong nature rarely exceed size 2 (Yes they can be bigger Matt, I know.....but it's rare).
What steepness to Wind Slabs start running assuming there are no persistent grains in the spx.
35-degrees
A student asks you why Persistent slabs are more dangerous (AKA they kill more people) than Storm slabs?
Because of their ability to propagate further, at lower, angles, and at times around terrain features that most avalanches could not wrap around.
What size avalanche do Deep persistent slabs typically release at?
D3-4 (if you said 5 that is cool too but wouldn't fall in the "typical" statement)
What Size do Wet Slabs most frequently release at?
Occasionally D2 (more frequent D2s than a DPS) but more frequently D3 and D4.
What steepness to Storm Slabs start running assuming there are now persistent grains involved?
35-degrees
With one predominant wind direction can wind slabs form on both sides of a ridge.
Not normally, they require the redistabution of a significant amount of snow to form.
New snow falls on a persistent grain that was formerly on the surface, is it a storm slab or a persistent slab?
Most avalanche centers will call it a storm slab until the storm stops (even NWAC). However, after 24-48 hrs of continuous snowfall (or the storm stops if its less will transition to calling it a persistent slab. Our avalanche center will use terms like run further, faster, and on lower angle terrain than you are used to.
Why are you bumming if you happen to trigger a Deep Persistent Slab besides the fact that it is gonna be HUGE?
Deep slabs most commonly release from well above their trigger to natural weak points with in the underlying the slab, which are most frequently well away (in all directions from the trigger (Assuming it was N)
What angle range are can wet slabs most frequently release at?
30-40 degrees or......30-45 (yes Matt)
What are some pros/cons of ECT's and PCTs for storm slabs?
ECT is a great test. PCT can be a great test but the layer must be clearly pre-identified beforehand (such as in a ECT/CT)
True or False: The avalanche problem that catches the most professionals is Wind Slab
True
Any sort of structure to the freshly fallen PP (AKA you can pick it up). Generally, once it gets to be 4F in stiffens it can be a problem, but certainly 1F. Pay attention to PEN ski as it can inform you how much settlement is going on with upper spx.
Discbite the steep terrain (30-45 degrees) that you would be willing to travel in if your main worry was a deep persistent slab.
Terrain that isn't big enough to produce a D3-D4 avalanche. Steep trees and even small steep openings are often fine. A Deep slab needs some space to get going.
How Frequent are Wet Slabs Human Triggered (A)?
Very Rarely AS (skier/snowboarder triggered), mostly N (Natural)
Why don't we generally give a F*** about storm slabs less than 20cm in thickness (assuming wind or FC are not playing a role).
There isn't enough thickness for the slab to be cohesive enough to propagate. If the upper slab is only F or 4F it will not have enough stiffness to propagate.
2-part: Are Wind Slabs generally Hard or Soft Slabs? What size do storm slabs rarely exceed?
They are generally hard but can be either soft or hard. Even though they are hard due to their formation being a finite range of redistributed snow they exceed size 2 (Yes they can be bigger Matt, I know.....but it's rare).
FC formation: On the snow, grain-sized level ice sublimates from a solid to a glass, if there is a low-temperature gradient and as a result very little Vapor pressure, what does the vapor once it has sublimated into a gas from the tip of a PP?
Stagnates in-between the grains and condenses, reverting back to a solid generally transfering from convex areas that to concave areas
If you dig a snow profile approximately 2m wide to access a layer 160cm down (so you are digging a little deeper approximately how much weight in snow will you move?
If you average 200kg per cubic meter (which is mostly 1F-P snow (of note F snow is 40-50kg per cubic meter and 4F is roughly 100kg) you would move roughly 800kg (1700 pounds)
Describe how Wet Slabs release when a persistent Grain is not present
Water in the upper spx creates strong over overweak and if a crack can become self-propagating causing a collapse a slab avalanche will release.
What are the three ways a storm slab forms
Warmer/denser snow falling on colder drier, less dense snow
PP change within the storm (generally smaller particles falling on bigger ones)
Big PPs within the storm
Bonus answer PPgp
What snow profile tests are most useful for a Wind Slab.
Snow Profile tests are much less helpful for wind slabs than all other slabs due to their very unpredictable nature with extensive spacial variability....all the time. (AKA the answer is None or the "suck" for wind slabs). This is because you don't know where the thickest or thinnest parts of the wind slab are without actually being on it and it is hard to compare results from one wind slab to another.
Why three reasons snow adjacent to crusts (MFcr) has the potential to facets more quickly
-There is already a "higher" level of moisture/vapor pressure a crust when compared to snow (PP/DF/RG) so if conditions allow AKA a high-temperature gradient) and the moisture moves it has the potential to FC that snow more quickly.
-Crusts (MFcr take longer to find an equilibrium of temperature) with adjacent snow (PP/DF/RG) layers because MFce are denser allowing them to stay colder longer.
-When on the surface, they have the ability to get "colder" than dry snow under the exact same do a higher volume of evaporation.
Creep and Glide are one of the most common Natural triggers of Deep Persistent Slabs. Explain how Creep and Glide work.
As the snowpack settles/rounds at different rates within the snowpack. As this happens the different layers decrease height/thickness but each layer at different rates. Now you put this on a slope (add angle tp the spx) and now the force of gravity pulling on the snowpack downhill, and the layers "want" to move downhill at slightly different rates stressing the interfaces and potentially causing a crack which if it has enough energy to self-propagate will cause the avalanche to release.
Is Water percolating down to a deeply buried weak layer causing it to avalanche a wet slab or a Deep persistent/persistent slab?
Good question; depends on the time of year and the region. Deep avalanches failing on a deeply buried persistent layer that was triggered due to water in the spx has been called both.