Understanding what triggers an avalanche is essential. Not only for those who live in the mountains, but also for adventurous snowboarders… like us!
This knowledge can be the key to survival. As a backcountry guide, it has certainly helped with my own avalanche mitigation strategies.
I’m therefore going to focus on one simple question today; what causes an avalanche?
Table of Contents
The Importance of Understanding Avalanches
An awareness of the causes of an avalanche leads to the better prediction and prevention of them. This allows us to take more measured risks, potentially saving life and limb. So keep reading!
What Causes an Avalanche?
An avalanche occurs when layers of snow collapse and tumble downhill. Avalanches are caused by a combination of factors including weather, temperature, slope steepness, snowpack conditions, and, importantly, human or natural triggers.
Let’s take a closer look at these all-important factors!
1. Natural Triggers
Many avalanches are triggered naturally, without any human interaction. The conditions in which the snow accumulates will significantly influence the likelihood of an avalanche.
Heavy snowfall over a short period increases the risk of avalanches. The additional weight and stress on the snowpack can cause it to collapse, particularly if the new snow is wet and heavy.
The condition of the snow already on the ground is equally important. A weak layer of snow can collapse under the weight of new snow, leading to an avalanche.
Temperature plays a critical role in the stability of snowpack. Warm temperatures can cause snow to melt and become heavier, while rapid cooling can create weak layers in the snowpack.
Saving your gnarliest lines for the afternoon is therefore a big mistake. By then, the sun has warmed the snow, melting important layers under the snowpack. In fact, most Everest summits are achieved at the crack of dawn – for this very reason.
Rain can add weight and water to the snowpack, while also making the snowpack slippery. Both of these conditions increase the likelihood of an avalanche.
Wind can transport snow from one area to another, overloading certain slopes and creating unstable conditions.
You’ll often hear backcountry guides and snowboarders talk about “wind lips”. These overweighted sections are prone to sliding, and should be avoided.
2. Human Triggers
Human activities are sadly a very common cause of avalanche. Despite their seemingly innocuous nature, human actions can significantly disturb the delicate balance within a snowpack.
Skiing and Snowboarding
The pressure from a skier or snowboarder crossing a slope can trigger an avalanche, especially if the snowpack is already unstable.
In fact, snowboarders can put up to 5 times their bodyweight through the snowpack during a turn [source].
Similar to skiing and snowboarding, the weight and vibration caused by snowmobiles can disturb the snowpack, triggering an avalanche.
These machines are super heavy. It doesn’t take a genius to imagine the risks involved!
Explosives and Avalanche Control Measures
Ironically, measures taken to control avalanches, like the use of explosives to trigger small avalanches, can sometimes cause larger, unintended avalanches.
Construction and Deforestation
Construction work and deforestation can alter the natural terrain, making certain slopes more susceptible to avalanche.
Humans have a tendency to remove the stabilizing vegetation (cut down trees!). This alters the snowpack and clears the pathway, allowing avalanches to continue once they’re been triggered.
3. Geographical and Geological Factors
The geographical and geological characteristics of a region will massively contribute to its susceptibility to avalanches. Understanding these is an absolute must for snowboarders!
Slope Steepness and Orientation
Avalanches are more likely to occur on slopes that are steep enough to allow snow to slide, typically between 30 to 45 degrees. Coincidentally, this is the gradient favored by most advanced skiers and snowboarders!
Steeper slopes than this tend not to slide, as they hold less snow. Shallower slopes can slide to a degree, but there is rarely enough momentum for it to be significant.
The orientation of the slope (whether it faces north or south) can also affect snow stability.
Snowpack Layering and Terrain
The way snow layers form and bond to each other plays a crucial role in avalanche risk. Varied terrain can create inconsistent snowpack, leading to a higher risk of avalanches.
You’ll often see backcountry experts doing a “snowpack” or “snow stability test” before heading out. The presence of a weak layer is often enough to deter them from riding. And rightfully so!
Vegetation and Ground Cover
Vegetation can anchor the snow in place, reducing the risk of avalanches. Conversely, sparse vegetation or rocky ground can contribute to a less stable snowpack.
4. The Weather
The weather isn’t just a topic of casual conversation; it’s a crucial factor in the formation and triggering of avalanches.
Snowstorms can rapidly increase the load on the snowpack, especially when accompanied by strong winds. The additional weight and stress can cause weak layers within the snowpack to collapse, leading to avalanches.
As touched on earlier, temperature changes have a significant impact on snow stability. Fluctuations between warm and cold temperatures can create weak layers within the snowpack.
Rain and Melting Events
Rain or melting snow adds weight and moisture to a snowpack, both of which can compromise its stability and increase the likelihood of avalanches.
Understanding the different types of avalanches can help you better appreciate the conditions that lead to them.
A slab avalanche occurs when a cohesive layer of snow collapses and slides over another layer of snow beneath it. These are typically more dangerous due to their larger size and ability to carry and bury objects in their path.
Slab avalanches are known for their ability to propagate across slopes and potentially carry a deadly mass of snow, slab avalanches pose a significant threat to mountain adventurers.
Unfortunately, these are seen all too often in the skiing and snowboarding world.
Wet vs Dry Avalanches
Wet avalanches occur when water penetrates the snowpack, either from melting or rain, reducing its cohesion. Dry avalanches occur in colder conditions when the snowpack remains dry.
Loose Snow Avalanches
These avalanches occur when loose snow on the surface slides over a cohesive layer of snow beneath. They usually start at a single point and fan out as they descend, resembling an inverted “V”.
Prevention and Mitigation
Equipped with an understanding of what causes an avalanche, it’s possible to develop strategies to prevent or mitigate their devastating effects.
Avalanche Forecasting and Monitoring
Forecasting and monitoring involve analyzing snowpack stability, weather conditions, and avalanche activity to predict the likelihood of avalanches.
Pay attention to the official forecasts, but always consider your own “in-the-field” impressions and testing too.
If in doubt, don’t go out!
Controlled or “artificial” avalanches are deliberately triggered to reduce the threat of unexpected avalanches. This is typically done with explosives or other avalanche control equipment.
Public Awareness and Education
Educating the public about the dangers of avalanches and how to avoid triggering them is crucial. This includes providing information on safe practices in avalanche-prone areas.
Examining past avalanches can provide invaluable insights into how and why avalanches occur. This helps to inform future prevention and response strategies.
Historical Avalanches and Their Causes
Discussing notable avalanches, their triggers, and their impacts can provide a deeper understanding of the risks associated with living in or exploring the snowy mountainous regions.
Each avalanche event offers unique lessons that can be used to enhance prevention measures and improve emergency responses in the future.
How Do Skiers and Snowboarders Trigger Avalanches?
We’ve established a multitude of potential avalanche triggers. But maybe we should specifically explore one aspect in a little more detail… That’s right. Skiers and snowboarders!
The allure of fresh, untouched snow is almost irresistible to snow sports enthusiasts. However, our quest for the perfect ride often places us in the heart of avalanche terrain.
By understanding how our actions can trigger these terrifying snow slides, we can better prepare ourselves to face, and hopefully avoid, the inherent dangers of the mountains.
The Pressure Factor
As snowboarders or skiers carve across the slope, the pressure exerted on the snowpack below is massive!
This pressure can collapse any weak layers of snow buried beneath the surface. This sets off a chain reaction, culminating in an avalanche.
It’s often the first few riders on a fresh slope who are most at risk, as they may be the first to encounter these unstable layers.
However… as we’ve discussed above, there are a host of factors at play.
Just because other riders have ridden there safely, doesn’t mean that another factor won’t come into play (temperature, precipitation etc). Proceed with caution.
The vibrations caused by zooming across the snow can also disturb the snowpack’s structure. These vibrations can travel through the snow, agitating weak layers and potentially initiating a slide.
This is especially true in the case of high-speed descents or jumps landing in fragile snowpack areas.
Cornices are overhanging edges of snow formed by wind. Cutting across or landing on a cornice can cause it to break, triggering an avalanche on the slope below.
Snowboarders and skiers must exercise caution near cornices, as their collapse can lead to a very significant avalanche.
Going off-piste, or venturing outside designated ski areas, means tackling unmanaged, avalanche-prone terrain.
Here, the snowpack is not monitored or controlled for avalanche risk, and the danger of triggering an avalanche is considerably higher.
Reducing the Risk: A Snowboarder’s Guide
Snowboarding in avalanche-prone terrains comes with inherent risks, we all know that!
But with proper awareness and a few precautionary measures, the danger of triggering an avalanche can be significantly reduced.
Here’s a few tips to help snowboarders (and skiers) minimize their avalanche risk:
On the Slope
- Ride One at a Time: When in avalanche terrain, it’s advisable to ride risky slopes one by one. This will significantly reduce the weight put through the snowpack. If an avalanche is still triggered, there’s also a higher chance that others in the group can rescue any buried riders.
- Avoiding Traversing Above Others: Traversing above other riders or groups can inadvertently put them in danger. There’s always a risk of disturbing the snowpack, triggering an avalanche above them. Be mindful of your line and the potential risks to others.
- Choosing Safer Routes: Opt for routes that are less steep, and avoid slopes with obvious signs of instability… such as recent avalanche activity, cracking, or collapsing snow.
Education and Awareness
- Avalanche Safety Courses: Enrolling in an avalanche safety course is a pivotal step in understanding the risks. These courses teach crucial skills like recognizing avalanche terrain and understanding snowpack conditions.
- Staying Informed: Keep yourself updated with the latest avalanche forecasts and snow conditions. Heed the advice of local avalanche forecast centers and make informed decisions accordingly.
- Avalanche Safety Equipment: Equip yourself with essential avalanche safety gear such as an avalanche transceiver, shovel, and probe. Familiarize yourself with how to use this equipment proficiently—it could save your life or someone else’s.
- Communication Devices: Carry reliable communication devices to stay in touch with your group and to reach emergency services if necessary.
Spot The Warning Signs
- Observing Snow Conditions: Look for signs of recent avalanche activity, shooting cracks, or whumphing sounds—all of which can indicate unstable snow.
- Checking Slope Angles: Most avalanches occur on slopes angled between 30 to 45 degrees. Use an inclinometer to measure slope angles and identify potentially dangerous terrains.
- Have a Plan: Before setting out, ensure you and your group have a well-thought-out emergency plan. Know the location of the nearest emergency services and have a clear communication strategy.
- Always use the Buddy System: You watch your buddies line, they watch yours. That way if something happens, you’ll be able to dive into action and locate them quickly.
Debunking Common Avalanche Myths
When it comes to avalanches, it’s crucial to separate fact from fiction. Let’s debunk some common avalanche myths:
Myth 1: Avalanches Only Occur During Storms
Reality: While storms can indeed trigger avalanches, avalanches can also occur on clear, sunny days, especially if the snowpack is unstable. The sun’s warmth can weaken the snowpack, increasing the avalanche risk.
Myth 2: Only Steep Slopes Are Prone to Avalanches
Reality: While slopes angled between 30 to 45 degrees are most prone to avalanches, they can also occur on lesser or greater slopes, especially if the snow conditions are unfavorable.
Myth 3: Making Noise Can Trigger Avalanches
Reality: It’s a widespread belief, but the vibrations caused by shouting or loud noises are not powerful enough to trigger avalanches. Avalanches are more likely triggered by the weight and vibration of a snowboarder or skier.
Myth 4: Avalanches Can Be Outrun
Reality: Avalanches can travel at speeds of up to 80 miles per hour within about five seconds of being triggered. Outrunning an avalanche is nearly impossible, making education and precautionary measures crucial for safety.
*Of course, there are videos of snowboarders evading avalanches. But these are often pro snowboarders, with a good measure of luck thrown in!
Myth 5: Avalanches Always Follow the Same Path
Reality: While avalanches do tend to follow natural channels, it’s not a rule. Each avalanche is unique, and the path can be influenced by a multitude of factors including snow conditions, slope angle, and obstacles.
Myth 6: Beacon, Shovel, and Probe Make You Avalanche-Proof
Reality: While having an avalanche beacon, shovel, and probe is essential, they do not make you invincible against avalanches. They are tools for rescue, not prevention.
Awareness, education, and adherence to safety protocols are the keys to minimizing avalanche risks.
Myth 7: Small Avalanches Are Not Dangerous
Reality: Even small avalanches carry a significant danger. They can easily knock you off your feet, resulting in falls, severe injuries, or even being buried.
The causes of avalanche are complex and innumerable. The least we can as snowboarders is minimize the chance of triggering one ourselves!
A key takeaway is therefore the need for proper education and preparation.
Being avalanche-aware means understanding the snowpack, recognizing the signs of unstable conditions, and having the equipment and knowledge to respond to an avalanche situation.
Before venturing onto the slopes, educate yourself on avalanche safety (which you’re doing by reading this), take an avalanche course, and gather the necessary safety gear.
It’s not just about our own safety either, but contributing to the broader safety of the mountain community.
Ride safe, my friend!