[MUSIC] Mountains are dynamic landscapes. Tectonics is pushing them ever upwards while erosion and gravity is pulling them back down to the ground. They're ever hammered by extreme weather. And the vertical relief found in mountains means that materials are constantly moving through them, coursing downwards and carving and denuding as they go. Whether it's water or snow, ice or rocks. Living in or visiting mountains carries risk. And in this lesson, we explore some of the really big hazards. We've already covered some hazards in the course, from crevasses and floods to acute mountain sickness and debris flows. Here we take a closer look at snow avalanches, landslides and volcanoes. Snow avalanches are the sudden release and movement of vast amount of snow down a mountainside under the influence of gravity and they're one of the most destructive forces in the nature. Thousands of people have been killed in avalanches over the centuries. If mountains were more heavily populated, the toll would be even greater. Of course, countless number of avalanches occur every winter and only a fraction of them were observed or recorded. But as the number of people living and recreating in mountains increases, the potential for avalanche danger increases as well. People have long recognized avalanches as a significant natural hazard. Early records from the European Alps, for example, reveal considerable avalanche destruction. There, avalanches became a sizable problem between the 16th and the 18th centuries when increasing population and widespread cutting of mountain forests coincided with increased snowfall in the glacial advance associated with the Little Ice Age. However, one of the greatest disasters came a little later, during the first world war. When a series of enormous snow slides on the Austrian Italian front killed 10,000 soldiers in a single day. In North America, the first major problems with avalanches arose during the 1800s Gold Rush era, when prospectors flooded into the mountain west and numerous mining towns were established. The earliest recorded avalanche fatalities in Canada, however, were not from the west side of the country but rather the east. In the winter of 1782, 22 people lost their lives to an avalanche in an Inuit settlement near Nain, Newfoundland and Labrador. Founded in 1771, Nain is the most northern and largest community in Nunatsiavut, and the gateway to Torngat Mountains National Park. The deadliest avalanche in Canada occurred on the other side of the country, nearly 120 years later. On the night of March 4th, 1910, 58 workers were killed as they were clearing a section of railway in Rogers Pass, the height of the Columbia Mountains in British Columbia. The rail line had been covered by an earlier avalanche when another slide came down on top of the workers. These examples are hardly anomalies. Today more people than ever travel through or live near avalanche terrain. And history has shown that everyone needs to be aware of the potential danger. When snow falls in the mountains, it accumulates in layers within the snowpack, the total amount of snow on the ground. Different weather conditions and snow fall events create different types of layers of snow over the course of a winter season. The stability of snow pack is influenced by how well different layers of snow adhere to one another and the surface upon to which they fell. This bond and anchorage of snow layers is called shear strength. And it resists the down slope force of gravity which is called shear stress. Simply put, when shear stress outweighs the shear strength, an unstable mass of snow breaks loose, creating a snow avalanche. Avalanches range in size from small sloughs that wouldn't harm a person to large powerful slides capable of destroying forests or even small villages. Sometimes considerable quantities of mud, or rock and timber are carried along with avalanches, all increasing their destructive potential. There are two principal types of snow avalanches, loose-snow avalanches and slab avalanches. And the distinction between the two is based on the cohesiveness of snow. Loose-snow avalanches have very little internal cohesion hence the name loose-snow. They're also sometimes called point release avalanches because they start when a small amount of loose snow, sometimes just the size of a snowball, slips and begins to slide down the slope, sending additional snow in motion. Again, these avalanches initiate at a point and they tend to grow wider as they slide. Loose snow avalanches occur much more frequently in freshly fallen snow on steep slopes. They're generally shallow, small and cause little damage, and scores of these slides can occur during a single snow storm. However, in the spring when the snow is wet and heavy, loose snow avalanches can gain enough momentum and mass to cause serious damage and so they're not to be taken lightly. Slab avalanches, on the other hand occur much less frequently but are considerably more dangerous. They occur when a plate or a slab of cohesive snow begins to slide as a unit before breaking up. For a slab avalanche to occur, you generally need four things. First, you need a slab of snow, which is typically a dense mass sitting upon a weak layer, or a layer of less cohesive strength. So the slab, sitting on top of a weak layer, has to be on a steep slope. How steep? Slopes that are typically steeper than 30 degrees. In fact, the majority of avalanches occur on slopes from 36 to 39 degrees. Slopes that are steeper than 60 degrees usually can't hold snow because they're too steep. Continuous sloughing keeps them fairly clean. So, you need a slab sitting on top of a weak layer, on a steep slope. And the fourth and final thing that you need is a trigger. Now slab avalanches can lie teetering on the verge of release sometimes for days, even months. The weak layers beneath the slabs can be extremely sensitive and any rapid addition of weight or stress can initiate a failure in a slope that would not have avalanched otherwise. Most avalanches are triggered when slopes are loaded by additional or new snow. Additional or new snow would be referred to as a natural trigger. Other types of natural triggers include warming temperatures, rainfall, rockfall, even an earthquake. Sometimes all it takes is the weight of just one person. In fact the majority of avalanches that injure or bury people are triggered by people, quite often the victim or the member of the same group. Wild life too can trigger avalanches. And these are examples of artificial triggers. We'll learn more about artificial triggers in a moment, because they're not always unintentional. Slab avalanches can originate in all types of snow, from old to freshly fallen snow, from dry snow to wet snow. Again, the chief distinguishing characteristic is that snow breaks away with enough internal cohesion to act as a single unit until it disaggregates or breaks up during its down slope journey. The area of release is marked by a distinctive upper fracture line, or crown, which is perpendicular to the slope and extends down to a well defined sliding surface, or bed surface. The size of the slab avalanche depends on a lot of factors. But it's often confined to a specific area on the slope, because of the nature of the terrain. However, during times of extreme instability, whole mountainsides may become involved with fracture lines racing along everywhere for several kilometers, releasing numerous avalanches down several different paths. Slab avalanches can be very destructive to vegetation or anything else in their path for that matter. On many mountain sides you can see where avalanches typically run at or below tree line. Slide paths are a common feature on the landscape, immediately recognizable due to their lack of trees. Avalanche paths have three major sections or zones. The starting zone, which is the uppermost part of the avalanche path. For a loose snow avalanche it's where the first snow grains start to move downhill. For a slab avalanche, it's where that crown is located. The second is the track. And the track is the area within which a particular avalanche travels. And the track is obviously downhill of the starting zone. And is usually treeless or has less trees or smaller trees than the surrounding vegetation. The run-out zone is where the debris from the avalanche accumulates at the bottom of the slope. Most avalanches have a flowing component, which consist of relatively dense snow. And the speed at which avalanches travel range widely. Typically dry slides can reach speeds of 50 to 200 kilometers per hour. When dry flowing avalanches exceed 35 kilometers an hour, a dust or powder cloud of airborne particles of snow is created and it moves above the denser flowing part of the avalanche. Of course, the forces are greatest in that dense flowing part of the avalanche. But if the slide is big enough, air blast from a powder cloud can travel fast enough to explode lungs if caught by the full impact of the blast. They can cause damage well beyond the normal avalanche zone. The extreme violence inside the flowing debris grinds up snow into even finer and finer particles. Even if the snow started out light and fluffy, it can become very dense by the time it finally comes to a stop. Small grains sinter, or coalesce, much more quickly than large grains. And the tiny grains making up avalanche debris can sinter as much as 10,000 times faster than the larger grains of the initial slab. Finally, all of that kinetic energy liberated on the way down heats snow just enough to create water on the surface of the ice grains. And it's for all of these reasons. It's easy to see why avalanche debris seizes up like concrete the instant when it comes to a stop. Wet snow avalanches on the other hand tend to generally slide at much slower speeds with no particular dust cloud. But they're impressive mass can still cause great damage. This is especially the case in the spring with large climax avalanches when the whole of the season's snow pack may release right down to the ground. Professional avalanche safety programs to protect the public require special procedures and strategies to mitigate avalanche hazards based on precise observations and meticulous research. Locating the danger, understanding the hazard, and assessing the risk are all critical strategies. While history has shown that avoidance is the safest strategy, there are times and places for defense and attack. Nobody knows this better than Jeff Goodrich, a senior avalanche forecaster with Parks Canada. Jeff and his team are responsible for safety along the stretch of the Trans-Canada Highway that crosses Rogers Pass. Let's visit with Jeff to learn about the various ways that Parks Canada manages this mountain hazard. So Jeff, where are we today? >> We're in the Rogers Pass snow study plot in Glacier National Park. And in Glacier National Park you've got a really important snow safety program. What is unique about this place? Why is it so important, that program here? >> A snow safety program is really important in Glacier National Park primarily because we have a very important transportation corridor that comes through, the Trans-Canada Highway and the CPR mainline that connects the east and west of Canada. We also have the mountainous terrain. So we have 134 avalanche paths within a 40 kilometer stretch of highway. We get up to 14 meters of snow up at treeline an average per season. >> So you have 134 avalanche paths in a span of 40 kilometers with 14 meters of annual snow. >> That's right. >> So, a considerable hazard. >> That's correct. >> How do you and your team mitigate those hazards, how do you deal with them? >> Our main ways of dealing with that are avalanche forecasting. We have static defenses, and we have an active artillery control program. So our forecasting program, we do a number of observations. We do weather, snow pack and avalanche observations. So for our weather observations, we are looking at snowfall, precipitation, we are looking at temperatures and wind speeds and direction. For our avalanches, we are looking at are avalanches running, how far are they running, how large can they be and then we also look at the snow cover. So we're looking at the layering in the snow pack and looking for weak layers, and testing those weak layers to see if they're likely to trigger into an avalanche. >> That's observation and analysis, but what about the defenses that you mentioned? Can you give us a tour? >> Sure, let's go. Behind me is one example of one of our avalanche snow sheds. So we have five snow sheds through this area of the pass, and they're really key to keeping the highway open in the winter. The way they're designed, is there's an avalanche pass above. And you can't quite see it but there's avalanche berms on either side that channel the avalanche debris over the snow shed. That allows the avalanche to pass over the snow shed and not bury the highway. So pretty key to keeping this whole show going during the winter. >> Yes, absolutely. >> Okay, so this is a great example of a static defense, but what about an active defense? >> This is an example of one of our active defense methods. So, let's say a 105 mm howitzer. This is actually a museum piece and was gifted to us from the Department of National Defense. So Jeff are you telling us that Parks Canada staffers are firing howitzers up into the peaks during the winter? >> No, that's where our partnership with the Department of National Defense comes in. So Parks Canada does the avalanche forecasting, and snow science, but the military actually fire and maintain the weapons. So they'll operate the weapons and fire the artillery up into the mountains to our avalanche start zones and bring the avalanches and snow down. >> How accurate are the howitzers? >> They're very accurate. We can fire rounds in and they can land within meters of their designated target. [SOUND] >> Fire. >> Clear! >> Clear! [SOUND] [MUSIC] [INAUDIBLE] >> Do you think we could fire one? >> No [LAUGH].
