Outforia Quicktake: Key Takeaways
- Avalanches are rapid snow movements that can be triggered naturally or by human activities.
- They usually occur on slopes between 30 and 45 degrees and can reach speeds up to 80 mph.
- There are several types of avalanches, including slab, loose snow, wet, and icefall avalanches.
- Factors influencing avalanches include slope, snowpack, and triggers such as weather conditions or human activity.
- Avalanches can be dangerous and deadly, affecting infrastructure, transportation, and the environment.
Avalanches are large amounts of snow that barrel down slopes at rapid speeds. They occur naturally, but can be triggered by human activity.
Most avalanches occur on slopes between 30 and 45 degrees. They can reach speeds up to 80 mph (129 kph).
Skiing, snowmobiling, and mountain hiking activities amongst other things can trigger avalanches. Outdoor enthusiasts that visit mountainous locations with steep slopes and snow should be cautious of avalanche conditions.
Since avalanches can happen very fast, it’s important to know what causes them. Understanding the causes can help you identify potential avalanche signs.
It’s also important to be educated on what to do if you get caught in an avalanche and how to rescue others if they get buried in the fallen snow.
Types of Avalanches
There are several types of avalanches that can occur. Each type has specific characteristics. They can also differ depending on weather conditions. Some avalanches pose a more serious threat than others. However, all avalanche signs and events should be treated seriously and with caution.
A slab avalanche is one of the most deadly types of avalanches that occur in North America. In avalanche terms, a slab is a plate of snow that glides as one unit off another layer of snow. When the bond between a slab and the layer of snow beneath weakens, it causes an avalanche.
Slabs are fast-moving, large pieces of snow. A slab can be as large as 50 yards (45.7 m). They can reach up to 20 mph (32 kph) in just a few seconds. Within the first 10 seconds of the slab sliding, it can reach speeds up to 80 mph (129 kph).
Slabs can be sensitive to weight as people travel over them. If the bond between a slab and snow is unstable, simply walking on the slab can cause it to break and slide down.
Loose Snow Avalanche
Loose snow avalanches involve loose snow sliding down a slope or mountainside. These avalanches aren’t as serious as slab avalanches. However, they can still damage buildings and injure or kill victims.
A loose snow avalanche begins at the point release. As it travels down a slope, it begins fanning outward. Smaller loose snow avalanches are called sluffs.
A loose snow avalanche can cause victims to be knocked off cliffs or trap them in crevices.
Wet avalanches occur when it rains or when temperatures are higher. Melting water or rain seeps into the snow. This causes the bond between snowpack layers to weaken.
Snowpack is snow that has been packed down from recurring snowfall. The layers build up as temperatures stay below freezing.
Each snowfall after the other contributes to the snowpack layers becoming more compact and bonded. When water separates the snowpack, it can create an avalanche hazard.
Wet avalanches are much slower than slab avalanches. This is because wet snow travels at a slower speed. These avalanches typically don’t reach anymore than 20 mph (32 kph).
Icefall avalanches resemble waterfalls, but in the form of ice. Glaciers can slide over a cliff and create an icefall avalanche. Icefall avalanches are triggered by falling blocks of ice.
Ice blocks falling disrupt the snow beneath it. These avalanches can be more difficult to predict because they can occur randomly. Warmer temperatures often trigger an icefall avalanche.
Glide avalanches are slow-moving units of snowpack. A weakened bond between snowpack layers can cause one of the layers to separate. This causes the entire snowpack layer to separate and form an avalanche.
A glide avalanche can last for hours or days. Warmer temperatures that cause water to melt can alter the snowpack layers. These avalanches are most common in wet climates. But they can also occur in dry climates when temperatures begin to rise.
Although not as common, these avalanches can happen in the winter if temperatures are high enough.
Unlike most avalanches, slush avalanches can occur on gentle slopes. They occur at an average angle between 5-20 degrees.
Slush avalanches aren’t very common because they usually only occur in specific northern latitude regions.
A slush avalanche happens when water builds up in impermeable permafrost soils. The water weakens the snowpack as it saturates it. This forms a slushy snow that can slide down gentle slopes for long distances.
Cornice Fall Avalanche
Cornices are ledges of snow that hang over a ridge or mountain crest. Although they can be a beautiful sight, they can also be dangerous to travel on. Cornices can form as wind picks snow up and pushes it onto the side of a ridge or mountain crest.
When a cornice falls, it can affect the snow beneath it. This can cause a cornice fall avalanche. These avalanches can fan out as they slide down the slope.
Winds, rapid warming, melting, and snow storms can trigger cornice fall avalanches. The cornice can become more unstable as wind extends it outward.
Despite being a picturesque spot, a cornice should be examined before approaching it. The weight of a person or group can be enough to break a cornice off if it’s in an unstable condition.
What Causes an Avalanche?
There are several factors involved in avalanche occurrences. Three key ingredients needed for an avalanche to happen include:
Avalanches commonly occur on steeper slopes of 45 degrees or more. Most avalanches don’t occur on slopes any less than 20 degrees, except for slush avalanches.
Snowpack is important for determining avalanche conditions. If signs point to the snowpack being unstable, this creates likely avalanche conditions. Compact and well-bonded snowpack is less hazardous.
When snowpack is weakened, avalanche probability increases. The final factor included in avalanche creation is a trigger.
Triggers can be a wide range of things. Avalanche triggers include:
- Weakened snowpack
- Warm temperatures
- Melting snow or rain
- Human activity
Seasons are also important when considering the causes of avalanches. Winter and spring are the most vulnerable times for an avalanche to occur. This is because snow can build up in the winter and create layers upon layers of snow.
Early to mid-spring is dangerous because of freezing, melting, and refreezing. These changes can cause layers of snow to build unevenly.
Effects of an Avalanche
Avalanches can have disastrous effects on nearby infrastructure, transportation, and people. One of the most detrimental effects is victims that get trapped under multiple feet of snow.
Two of the main causes of death from avalanches is suffocation and hypothermia. Trauma from rocks and other obstacles can also cause severe injuries or death.
Towns and homes located near snowy mountain sides are vulnerable to avalanches. Areas prone to avalanches may have a barrier wall to help prevent the heavy snow from reaching roads or homes. But some avalanches are so large that they can travel over the barrier.
Avalanches can disrupt transportation by blocking roadways and railroad tracks. Frequent avalanches that disrupt transportation can impact the economy of an area.
Avalanches can also cause crop failures if the falling snow builds up on farmlands. Electricity and other utilities can also be affected.
Not only do avalanches pose a threat to humans, it can also cause harm to animals and their habitats.
Large avalanches are capable of clearing trees and other vegetation that animals call home. Animals, such as bighorn sheep and mountain goats, can die if they’re caught in an avalanche.
You may also like: 24 Types Of Natural Disasters That You Need To Know
Where Do Avalanches Occur?
In the right conditions, avalanches can occur almost anywhere there is snowpack and slopes. Colorado is one of the most common places avalanches occur in the United States. Wyoming, Montana, and other northwestern states also experience avalanches.
Canada experiences thousands of avalanches every year. They can occur in every region in Canada. Alberta, Yukon, and British Columbia mountain ranges are most vulnerable to avalanches.
Alpine countries in Europe experience the most avalanches, including:
Mountainous regions in other countries, such as Peru, can also experience avalanches. One of the deadliest avalanches in history occurred on the Huascarán mountain in Peru.
Avalanches occur in three main parts. It has a starting point, a track, and runout zone. The starting point of an avalanche is the highest or most steep part of a slope. An avalanche track is the area where the avalanche passes through.
Chute or tree clearings can be a sign that avalanches occur in an area frequently. An avalanche track can also include snow and debris piles from previous events.
The runout zone is the area where an avalanche ends. This is the area where snow and debris pileup is the highest. The runout zone can be the most deadly because victims are more likely to be buried in this zone.
You may also like: What is Subsidence and How Does it Affect the Earth?
When Do Avalanches Occur?
An avalanche can occur anytime throughout the year if the conditions are right. However, they’re most common between December and April in the US.
December through early February involves frequent and sometimes heavy snowfall. Heavy snowfall and snow storms create likely avalanche conditions.
Early and mid-spring introduces temperature changes that can alter snowpack bonds. As a result, avalanches are fairly common during the spring season. Avalanches are less likely during the summer. But they can still occur in higher altitudes that experience freezing temperatures.
January through March marks the deadliest times for avalanches in the US. Snowfall in high altitude, mountainous areas are heavier in these months.
You may also like: 23 Types Of Mountains: Your Definitive Guide
The Dangers of an Avalanche
Avalanches can be extremely dangerous to skiers, backcountry climbers, hikers, snowmobilers, and snowboarders. When an avalanche occurs, it can carry its victims down the slope with it. In the process, large amounts of snow can bury people.
Most avalanche deaths are caused by people being buried and unable to be rescued. If you don’t have the right gear handy, it can be extremely difficult to find and dig out a person buried in an avalanche.
To reduce the risk of falling victim to an avalanche, there are a few things you can bring along during your trip to be more prepared.
Avalanche gear can potentially save you or another victim’s life if you’re involved in an avalanche.
Some gear recommended for anyone visiting areas where avalanches occur include:
- Portable shovel
- Avalanche beacon or transceiver
- Avalanche probe
These tools can be used to assess snowpack layers and rescue victims that were caught in an avalanche. Digging out someone who’s buried in snow can take 45 minutes or more. Bringing a portable shovel along can reduce this time to just 10 minutes.
An avalanche beacon or transceiver should be switched to “receive” when entering avalanche danger zones. This allows rescuers to find buried victims by the signal the transceiver emits.
Time is extremely important when avalanches happen. The survival rate of an individual buried in avalanche snow is reduced significantly with time. The first 15 minutes of when a victim is buried is critical.
You may also like: What Is A Tornado? A Complete Guide To Understanding Twisters
How Common Are Avalanches?
Avalanches have become more common because of increased recreational activity in mountainous regions. About 150 people die from avalanches around the world every year.
There were 17 fatalities caused by avalanches in the 2021-2022 season in the US. Most of the victims in these avalanches were snowmobilers, skiers, and mountain climbers. Colorado had the most fatalities.
In 2020-2021, there were 37 fatalities caused by avalanches in the US. Most of the victims were skiers and snowmobilers. Every winter in the US, an average of 28 people die from an avalanche event.
According to European Avalanche Warning Services, an average of 100 deaths occur as a result of snow avalanches in Europe each year. Fatal avalanches that occurred in Europe so far in the 2022-2023 season were caused by wind slabs, persistent weak layers, and new snow.
You may also like: How Long Does It Take To Climb Mount Everest? Everything You Need To Know
Some of the largest avalanches in history are believed to occur in the Himalayan mountain range. However, measurements and observations in this area are minimal.
The greatest avalanche measured occurred in 1885 in the Italian Alps. It was estimated to have about 3.5 million cubic meters (120 million cubic ft) of snow.
The deadliest avalanche in history was the 1970 Huascarán avalanche in Peru. It was a rock and ice avalanche that was triggered by a 7.75 magnitude earthquake. Several surrounding areas were devastated.
Approximately 28,000 people were buried in the avalanche and about 22,000 were killed. The death toll from the aftermath of the avalanche brought the number of fatalities even higher.
The deadliest avalanche recorded in the US took place in Wellington, Washington in 1910. It caused 96 deaths. The event occurred after the area had experienced a blistering 9-day blizzard. The avalanche hit two trains, one of which was holding passengers.
You may also like: Why Use Trekking Poles?: Advantages, Disadvantages & Pro Tips!
Can humans survive an avalanche?
Yes, humans can survive an avalanche. However, survival rates significantly decrease after the first 15 minutes from the start of the event. With proper safety and rescue gear, it’s possible for avalanche victims to be rescued.
Victims are less likely to survive if they’re buried and unable to be located. It’s extremely important that any witnesses nearby try to find buried avalanche victims within the first 15 minutes.
Some deaths may not be preventable if they occur from trauma caused by large rocks and other debris.
Are avalanches natural disasters?
Yes, an avalanche is a type of natural disaster. They are often caused by natural triggers, such as warming temperatures and uneven snowpack.
Human activity can trigger an avalanche to occur. But unstable snowpack and other conditions are involved when an avalanche is triggered by humans in a vulnerable area.
What are the signs of an avalanche?
There are a few warning signs that you can use to figure out whether an avalanche is likely. Evidence of clearings caused by previous avalanches may show you’re in a dangerous area.
If you notice any fractures in the snowpack or hear hollow, whumping sounds when walking, this is a sign that a slab might release. Recent significant warming or heavy snowfall creates hazardous avalanche conditions.
Are avalanches and landslides the same?
No, an avalanche and landslide are two different types of natural disasters. A landslide consists of rocks, dirt, and other debris that move down a slope. Avalanches involve slopes with snow.
Both include similar processes of things moving down a slope and posing a threat to humans and animals. But landslides can occur virtually anywhere with steep slopes.