Author Archive

Avalanche Problem Web Series:
Part 4 – Storm Slab

How to Apply the Avalanche Forecast to Your Riding

storm-snow

For splitboarders venturing into the backcountry, information can be the difference between an epic day and tragedy.  In an effort to increase education and avalanche awareness, Spark R&D is presenting a 7-part web series called Avalanche Problems, which will explain the nationally standardized types of slides most commonly described in advisories by avalanche forecasters.

Understanding the characteristics of each type will help to determine where avalanches are likely to occur and what kind of terrain should be avoided.  In today’s installment, we will cover Storm Slab Avalanches.

Storm slabs in a nutshell

storm-snowLet’s face it:  The best riding is often experienced during or right after a big storm. But in the backcountry, this can mean the new snow has formed a soft slab.  The new snow may not be adhered to the underlying surface, or it may have an “upside down” structure.   The best practice is to stay off of steep terrain (35 degrees and steeper) until the new snow has had time to adjust, which could take several days.

What exactly is a storm slab?

• A storm slab is new snow, which is cohesive enough to act like, or form a slab.
• Sometimes the slab is not bonding to the underlying surface. In other cases, it may form upside-down, meaning colder lighter snow on the bottom (weak layer) and heaver or wetter snow on top (slab). These tend to be smaller in size.
• If the storm snow is not a slab, than this is referred to as “loose dry” (next post). If a persistent weak layer is involved, than see the “persistent slab” problem.
• These are often short lived, and are experienced during or post storm event. The problem can last for several days, but can last longer if the temperatures remain very cold.

Where you might find a storm slab, and how to avoid them

storm-slab-icon• Storm slabs are typically widespread, but think about where the storm totals are greatest. Upper elevations, or the wet side of the range, are likely to have more of a problem.
• Higher elevations and shaded slopes are colder, which can preserve the problem for longer.
• Avalanches are more likely to occur in terrain 35 degrees or steeper.  However, play it safe and stick to terrain under 35 degrees during or after the storm.
• Always be careful around natural avalanche paths during a storm, as start zones are becoming loaded and natural slides can occur.

How to look for and test a storm slab

• Hand pits and skin track cuts are nice tests if storm totals are under 1.5 feet (about 40cm), as they are very quick, can be done many times throughout the day, and give information on how well the snow is bonding. They allow you to look for patterns throughout the day.
• Ski cuts or stomps on steep slopes are great indicators for these surface conditions.
• Compression Tests (CT) are good for testing the bonding (lower scores or sudden planer sheers), and Extended Column Tests work if the new snow isn’t too soft.

Tips: If you get out for a few days in a row, watch for settlement cones around trees and bushes. Also, look for trends in your test scores:  Higher scores, or more resistant hand sheers, mean the snow is starting to stick.

Disclaimer: Although characteristic, these descriptions are general, so make sure to read into any specifics mentioned on your local advisory. Also, this is just one piece of the puzzle, so remember to factor in the hazard rating and any field observations.

Find your local avalanche center: www.avalanche.org

Presented by Clark Corey
Splitboard Guide/Avalanche Educator

 

Avalanche Problem Web Series:
Part 3 – Deep Slab

How to Apply the Avalanche Forecast to Your Riding

deep-slab
For splitboarders venturing into the backcountry, information can be the difference between an epic day and tragedy.  In an effort to increase education and avalanche awareness, Spark R&D is presenting a 7-part web series called Avalanche Problems, which will explain the nationally standardized types of slides most commonly described in advisories by avalanche forecasters.

Understanding the characteristics of each type will help to determine where avalanches are likely to occur and what kind of terrain should be avoided.  In today’s installment, we will cover Deep Slab Avalanches.

Deep slab avalanches in a nutshell

deep-slabWhen deep slab conditions exist, it’s time to ratchet back the terrain and play it safe. Once persistent weak layers are buried deep in the snowpack, it becomes hard to test and evaluate them, and the consequences can be dire as the slide is going to be large. Read into the advisory on where these conditions might exist.  Until the layer has healed, either stick to lower angle terrain, or gravitate towards slopes where this structure isn’t present.  Be cautious of runouts when the weak layer has been recently loaded.

What exactly is a deep persistent slab?

• A deep slab is essentially a persistent slab, but thicker (see previous post). The slab is going to be approaching 3 feet or more. Sometimes it can even involve the season’s entire snowpack. This strong slab is resting on a softer, persistent weak layer beneath.
• For review, persistent weak layers include facets, depth hoar and surface hoar. These weak layers form under cold and clear conditions, and when buried under a slab, become very problematic.
• Deep slab conditions are very tricky. Because of the slab thickness and nature of persistent weak layers, they can produce very large, and often times un-survivable avalanches.
• Given the fact this involves a persistent weak layer, deep slabs can stick around. These can be problematic for weeks to months.
• Like the persistent slabs, after periods of warm weather and little additional stress, they can slowly being to heal.  After periods of being dormant, however, they can be reawakened if large loads are applied or drastic warm-ups occur.

Where you might find a deep slab, and how to avoid them 

• Deep slab problems are as widespread as the persistent weak layer. This means the layer can exist on many slopes and elevations (although this depends on how exactly they were formed), or it could be localized.
deep-slab-icon• Read your local advisory carefully for information on the distribution of this layer and think about where it existed before it got buried.
• When sensitive, very conservative decision-making is crucial. Stick to lower angle terrain (under 30 degrees) and be mindful of what’s above.
• Often times, before the layer fully heals, we enter a period of “low probability, high consequence”, meaning there’s a smaller chance you’d trigger it, but if you do, there’s a big price to pay.
• With this in mind, even when the layer is beginning to stabilize, try to avoid steep slopes with this structure. Your best bet is to read into the advisory to get an idea of where this layer exists (aspect and elevation) and avoid steep terrain in these areas.
• Stay away from rocky slopes or areas of shallower snow, as the weak layer is closer to the surface, and can be easier to trigger.
• Remote triggers are possible with this layer, so be aware of what’s above and be careful of runouts (especially if cracking/collapsing is experienced).
• Keep in mind that large avalanches mean safe zones must be selected carefully. These are the kind of slides that can run full path and are very destructive.

How to look and test a deep slab

deep-slab2

Example of deep slab pit analysis. Photos courtesy of Sawtooth National Forest Avalanche Center (sawtoothavalanche.com).

• Field observations become difficult, even for experienced professionals.
• Snowpack tests become less useful.  When a layer is that deep, tapping on a shovel is not always going to produce results. Instead, you can focus on structure, so dig just to look for the layer and check for hardness.
• Signs of natural avalanches as well as cracking or collapsing while touring certainly are indicators, although these signs won’t always be present.

Tips: Deep slabs can often produce “false stable” snowpack test results (ECT or CT), meaning the lack of failure in your tests make the conditions look more favorable than they actually are. Instead, if the structure is present (slab over weak layer), one could assume it’s possible to trigger in the right spot. Until the weak layer actually becomes stronger and firmer, it should not be trusted.

Disclaimer: Although characteristic, these descriptions are general, so make sure to read into any specifics mentioned on your local advisory. Also, this is just one piece of the puzzle, so remember to factor in the hazard rating and any field observations.

Find your local avalanche center: www.avalanche.org

Presented by Clark Corey
Splitboard Guide/Avalanche Educator

Avalanche Problem Web Series:
Part 2 – Persistent Slab

How to Apply the Avalanche Forecast to Your Riding

persistent-slab6For splitboarders venturing into the backcountry, information can be the difference between an epic day and tragedy.  In an effort to increase education and avalanche awareness, Spark R&D is presenting a 7-part web series called Avalanche Problems, which will explain the nationally standardized types of slides most commonly described in advisories by avalanche forecasters.  

Understanding the characteristics of each type will help to determine where avalanches are likely to occur and what kind of terrain should be avoided.  In today’s installment, we will cover Persistent Slab Avalanches.

Persistent slabs in a nutshell

persistent-slabWhen facets, depth hoar or surface hoar become buried, we are faced with an avalanche problem that can last for a long time and be widespread. The best strategy may be to seek out lower angle terrain until the layer has had time to heal. Be especially careful around trigger points, such as rocks, shallow spots and roll-overs. These slides are know for their ability to produce large avalanches.

What exactly is a persistent slab?

• A slab of cohesive snow (layer that is sticking together) that is sitting on top of a persistent weak layer.
• Examples of persistent weak layers include facets, depth hoar (developed facets) or surface hoar (frozen dew).
• These layers are all formed during periods of clear, calm and cold weather, and can be enhanced by shallow, early season snow, which is subsequently buried by following storms.
• Persistent slab conditions can produce large avalanches.
• Persistent weak layers are given this name for a reason:  When these layers form and get buried, they tend to last for weeks, or even months.
• Warm weather and time may eventually compact persistent weak layer, making them stronger.
• Be careful though, because more loading (new snow or wind), or drastic warm ups, can reactivate these weak layers.

Where you might find a persistent slab, and how to avoid them 

• Unfortunately, persistent weak layers can be widespread, meaning the layer exists on many slopes and elevations (although this depends on how exactly they were formed).
persistent-slab-icon• Assume the layer is everywhere unless the forecast mentions otherwise. Read your local advisory carefully for information on the distribution of this layer.
• Areas of concern can include shallower snow, rocky slopes, or colder, protected slopes, like mid-elevation, shaded terrain.
• The only option is to seek out lower angle terrain (30 degrees or less) and be conservative.
• As the weak layer begins to heal and the forecast hazard starts to go down, gradually progress into terrain above 30 degrees. Pick slopes with clean runouts, no convexities or trigger points, and lower consequence. Pick safe zones wisely and make sure to use good travel technique.
• Remote triggers are possible with this layer, so be aware of what’s above and be careful of runouts (especially if cracking/collapsing is experienced).

How to look for and test persistent slabs

persistent-slab3

Photos courtesy of Sawtooth National Forest Avalanche Center (sawtoothavalanche.com).

• Relevant observations include watching for natural avalanches as well as cracking or collapsing while touring. This means the persistent weak layer is giving way under the weight of the slab and yourself, so just imagine if this happened on a steeper slope!
• By checking the forecast, you may have an idea of how deep the layer should be, so try digging several pits and observe where the layer exists. Facets often have a “sugary” or “granular” appearance, and do not pack into snowballs well.
• Performing snowpack tests, such as an Extended Column Test, can give us more information. It is important, however, to have the training and experience necessary to properly interpret the test results. (If you haven’t done so already, take an avalanche safety course!)
• Pushing your pole into the snow and feeling for a sudden decrease in resistance means you’ve punched through the slab into the weak layer. This can be a quick way of tracking the layer’s distribution throughout the day.

Tips: Don’t make any assumptions about persistent weak layers. They can be tricky to deal with, catch you off guard, and often produce large avalanches.

Disclaimer: Although characteristic, these descriptions are general, so make sure to read into any specifics mentioned on your local advisory. Also, this is just one piece of the puzzle, so remember to factor in the hazard rating and any field observations.

Find your local avalanche center: www.avalanche.org

Presented by Clark Corey
Splitboard Guide/Avalanche Educator

Avalanche Problem Web Series:
Part 1 – Wind Slab

How to Apply the Avalanche Forecast to Your Riding

windslab-resize

For splitboarders venturing into the backcountry, information can be the difference between an epic day and tragedy. In an effort to increase education and avalanche awareness, Spark R&D is presenting a 7-part web series called Avalanche Problems, which will explain the nationally standardized types of slides most commonly described in advisories by avalanche forecasters.

Understanding the characteristics of each type will help to determine where avalanches are likely to occur and what kind of terrain should be avoided. In today’s installment, we will cover Wind Slab Avalanches.

Wind slabs in a nutshell
wind-slabThese slabs are very common throughout the winter in just about every mountain range. They’re created by wind deposited snow and tend to live under cornices, below ridgelines, around the edges of gullies, and in most alpine terrain. After a wind event, your best bet is to avoid these types of terrain features and let them stabilize, which can take from a couple days to a week.

What exactly is a wind slab?
We often hear people speak of wind loading and wind slabs, so let’s talk about what exactly this is and how are they formed.

• When the wind blows snow across, or up the mountain, it gets deposited onto adjacent slopes, forming a slab (a cohesive unit or “chunk” of snow).
• As the snow grains are blown, they get broken into small particles. When these small grains come to rest, they pack tight together and form a nice slab of snow.
• The slope that the wind is blowing across and stripping snow from is called the windward slope. The side that the snow lands on, and is becoming loaded, is referred to as the leeward slope.
• The thickness can depend on the strength and duration of the wind, but also the amount of snow available for transport.

Where you might find a wind slab and how to avoid one:

• Typical areas include off ridgelines, below cornices (pointing towards the slab), around wind-slab-icongullies or ribs, and in any exposed alpine terrain.
• Most wind loading occurs in the alpine, at treeline, and in avalanche start zones (the tops of defined avalanche paths). During especially strong wind events, loading can be experienced mid slope and below treeline.
• Avoid leeward slopes and commonly wind loaded terrain features (mentioned above) during and post wind event.
• When venturing on slopes that do not appear to be wind loaded, keep in mind that loading can occur in pockets. Watch out for a change in surface texture.

How to look for and test a wind slab:

windslab-resize2

Photo courtesy of Sawtooth National Forest Avalanche Center (sawtoothavalanche.com).

• Visually inspect slopes: Look for pillow-like features; feel for drum-like or hollow sounds; watch for shooting cracks; and assess if a slab exists on lower angle terrain.
• Look for loading patterns. Stripped snow on one slope means it landed somewhere else. Local wind patterns often provide visual clues.
• Pay attention to what direction the wind has been blowing by reading the avalanche forecast, and keeping up to date on the weather forecast.
• Wind slabs are typically in the upper surface of the snowpack, so tests to determine bonding and sensitivity can be done quickly.

Tips: Wind can rapidly change conditions and load snow up to 10 times faster than it can fall from the sky. If the wind is really blowing, the avalanche danger can go from mild to wild very quickly.

Disclaimer: Although characteristic, these descriptions are general, so make sure to read into any specifics mentioned on your local advisory. Also, this is just one piece of the puzzle, so remember to factor in the hazard rating and any field observations.

Find your local avalanche center: www.avalanche.org

Presented by Clark Corey
Splitboard Guide/Avalanche Educator