Lesson 8 Flashcards
Define an avalanche.
The sudden release and movement of vast amounts of snow down a mountain side, under the influence of gravity.
In Europe, when did avalanches become a sizeable problem?
Between the 16th and 18th centuries - when increased population and the cutting of mountain forests coincided with the increasing snowfall and advancing glaciers of the little ice age.
Describe what happened during one of the greatest avalanche disasters in Europe.
During the First World War, enormous avalanches killed 10,000 soldiers in a single day on the Austrian-Italian front.
When did avalanches become a significant issue in North America?
During the 1800’s , during the Gold-Rush era, when prospectors settled into the mountainous west, and numerous mining towns were established.
When and where were the earliest avalanche deaths recorded in Canada?
In 1782 - when 22 people from an Inuit settlement near Newfoundland and Labrador were killed.
What national park is the Nain community closest to?
The Torngat Mountains National Park - North-Eastern Canada.
Describe what happened during the deadliest avalanche in Canada.
Occurred in Roger’s Pass, at the height of the Columbia mountains in BC, on March 4th in 1910. 58 workers were killed as they were trying to clear a section of railway. Another avalanche came down as they were trying to clear snow from a previous one.
Define Snowpack
The total amount of snow on the ground.
What determines the stability of snowpack?
How well the different layers of snow adhere to one another, and the surface on which they fell.
Describe sheer strength versus sheer stress.
Sheer strength is the bond and anchorage of snow layers to one another. Sheer stress is the downslope force of gravity on the snowpack.
When the sheer stress is greater than the sheer strength, an avalanche will occur.
What are the two main types of snow avalanches? The distinction between the two is based on what?
Loose-snow avalanches and slab avalanches. The distinction between the two is based on the cohesiveness of the snow.
What is another term for lose-snow avalanches?
Point-release avalanches - start small and get bigger.
Describe a loose-snow avalanches and slab.
Loose snow avalanches are caused by snow that have very little cohesion. They initiate at a point and tend to grow wider as they slide. The occur much more frequently in fresh fallen now on steep slopes. They are generally small, shallow and cause little damage. However, in the spring, when the snow carries more weight, they can be considerably dangerous.
When are loose-snow avalanches most dangerous?
In the spring, when the snow carries more weight.
What are slab avalanches?
Slab avalanches occur much less frequently, but are considerably more dangerous. They occur when a slab of cohesive snow begins to slide as a unit before breaking up.
What four things must be present for a slab avalanche to occur?
1 - a slab of snow (dense upper layer)
2 - A weak layer (underneath)
3 - A slope steeper than 30 degrees
4 - a trigger (natural or artificial)
Describe natural versus artificial slab avalanche triggers.
Natural: are things like freshly fallen snow or changes in weather
Artificial Triggers: are disturbances caused by humans or animals
The majority of avalanches occur on slopes that are how steep?
36-39 degrees
Why don’t avalanches occur on slopes as steep as 60 degrees?
Because continuous sluffing doesn’t allow the snow to build up.
True or false - the majority of avalanches that kill people are a result of natural triggers.
False - the majority of avalanches that kill people are triggered by people (often members of the same group).
In what types of snow do slab avalanches typically originate?
All types! - dry, wet, old, new
What is the term for the upper fracture line of a slab avalanche?
The crown - perpendicular to the slope and extending down to the sliding/bed surface.
What are the three major zones of an avalanche path?
1 - The starting zone (upper-most part)
2 - The track
3 - The runout zone (where debris accumulates at the bottom)
How fast can dry slide avalanches travel down the track?
50 - 200 Km per hour.
What happens when dry-flowing avalanches exceed 35 km per hour?
A powder cloud of airborne snow particles is formed. If the avalanche is big enough, the air blast from the powder cloud can be forceful enough to explode your lungs.
Why does snow from an avalanche feel very dense once it comes to a stop?
Because the violence during the slide, causes snow particles to sinter into a finer and finer powder. Meanwhile, the kinetic energy of the avalanche heats up the snow, creating a layer of water around the ice grains that freezes when the avalanche come to a stop - making the snow as hard as concrete.
Do wet-snow avalanches form a dust cloud?
No - they flow more slowly, but still carry large amounts of force.
What is the safest avalanche strategy?
Avoidance
How does Jeff Goodrich manage avalanches on the trans-Canada highway that goes through Roger’s Pass?
134 avalanche paths in a span of 14 kilometres
Avalanche forecasting - wind speed, snowpack, forecast
Static defenders - Avalanche snow sheds (avalanches pass over and highway passes through the tunnel)
Active Defense - Artillery control (military fires artillery up into the mountains , landing within meters of designated target)
What is a landslide?
The downslope movement of rock and debris - when sheer strength is less than the sheer stress placed on the rock
How does vegetation affect the sheer strength of a slope?
Vegetation increases the sheer strength of a slope - acting as a barrier for slow downslope movement, or a natural anchor for soils.
What natural features might increase the likelyhood of landslides?
Rivers and streams - can undercut slopes.
What man are features can contribute to the increased likelihood of a landslide occurrence?
Clear-cutting forests, building roads, mining as well as home-building.
What factors are used to classify the 6 types of landslides?
1 - The material composition
2 - The amount of water content
3 - How they move down slope
What are the 6 types of landslides?
1 - Rockfalls
2 - Topples
3 - Translational Slides
4 - Rotational Slides
5 - Earth Flows
6 - Debris Flows
Describe and distinguish between Rock Falls and Topples
Rock Falls and Topples are the most basic type of landslides. They occur when rocks suddenly detach from slopes.
Rock Falls - occur when the rock detaches and falls freely, bouncing down slope.
Topples - When the rock slab falls and rotates end over end down slope
Where are rock falls and topples most likely to occur?
Often occur on steep slopes with exposed, bare rock. They are mostly trigger by rain or freezing and thawing of the rock creating fractures and instability.
Describe the rock fall that occurred at Turtle mountain (one of the largest in Canadian history).
The rock fall at Turtle mountain (near Crowsnest Pass, Alberta Rockies), happened in the spring of 1903 when a large portion of the mountain collapsed (approx 82 tons of limestone). It buried most of the town of Frank and killed around 80 people. The unstable geology of Turtle mountain was the primary cause.
What factors contributed to the unstable geology of Turtle Mountain?
The nature of the techtonic plates of the Rockies, caused more dense, older rock to settle above lose, younger layers of rock.
Rain seeped into the lower layers and expanded when freezing, causing the cracks to be come larger.
The slope was very steep and nearly undercut, due to the erosion of glaciers as well.
Describe translational and rotational slides.
Occur when a place of weakness/failure surface in the rock causes an overlying mass to move downslope, over the surface of the rupture.
These landslides tend to happen in unconsolidated sediment (sand, clay silt) and are often triggered by increased moisture or an earthquake.
What is the most distinguishing characteristic of rotational or translational slides?
A deep head-scarp.
What is a Head Scarp?
A steep (nearly vertical), region of exposed soil and rock at the head of the landslide.
What distinguished whether or not a slide is translational or rotational?
How it moves down slope.
Describe how a translational versus a rotational slide moves down slope.
If the fracture line is parallel to the slope, this will cause a translational slide.
If the fracture line is concave upward, this will cause a rotational slide - which can be distinguished from translational slides because the land remains as more of an intact block, and the vegetation tends to tilt backwards (further upslope because of the rotation).
What is another term for a rotational slide?
A slump.
Describe Earth Flows and Debris Flows.
They involve the fluid-like movement of find sediments, downslope. They occur when these unconsolidated sediments become saturated with water and overlie an impermeable layer (preventing water drainage, and forcing sediment particles apart, decreasing friction.
What is the difference between an Earth Creep and an Earth Flow?
Earth Creeps are when the sediment moves very gradually downslope, when little water is present. Earth flows require more water and move much faster.
What is the difference between an earth flow and a debris flow?
While earth flows are primarily composed of fine sediment, debris flows are composed of larger sediment - like rocks or boulders.
What is the most dangerous type of landslide?
A debris flow - because they move fast and carry large, damaging debris with them.
- usually triggered by large influxes of water
- often follow courses of mountain streams, but can initiate anywhere on a slope that is sufficiently water saturated.
What might be used to protect roads and railways from areas that are at high risk of landslides?
Rock-fall shelters (like tunnels), or drape-nets on vertical rock cliffs, or catchment fences that catch falling rocks.
What can be built to prevent debris flow from flowing onto the land?
Levees and diversion structures
What efforts are taken to stabilize the land in areas that are at a high risk of a landslide?
1 - Metal anchors are driven in rock-faces
2 - Ditches, culverts and drains can be made to facilitate efficient run-off
3 - Tree-planting can also be used to help stabilize slopes
Where are volcanoes formed?
Convergent plate boundaries (subduction zones), divergent Plate boundaries and volcanic hotspots (not associated with plate boundaries).
Different types of magma are defined/differentiated by what?
The amount of silica - determining its viscosity and ability to flow.
True or false: Magma with a low silica content will have a high viscosity (flows less easily).
False - magma with high silica has a high viscosity and magma with low silica content will have a low viscosity.
Describe Basaltic Magma
Basaltic magma has a low silica content and therefor a low viscosity (meaning it flows easily). It contains large amounts of iron and magnesium, making it dark in colour. It reaches the earths surface WITHOUT passing through continental crusts and thus is typically seen at divergent plate boundaries.
What type of rock is formed by basaltic magma?
Basalt.
Other than divergent plate boundaries, where else can basaltic magma be seen?
Volcanic hotspots.
Where is Skaftafell National Park and what’s special about it?
Located in southern Iceland, Skaftafell National Park contains a beautiful waterfall with neat rock formations as a result of Basaltic magma.
Describe Rhyolitic Magma.
Rhyolitic magma has a high silica content (high viscosity) and low levels of iron and magnesium, making it a lighter colour.
How is Rhyolitic magma formed?
When Basaltic magma rises between continental crusts, it pulls silica from the silica-rich granite rock, that forms most of the earths crust. With the higher silica content, it becomes Rhyolitic magma.
What rock is formed by Rhyolitic magma?
Rhyolite rock.
Where is Rhyolitic magma most commonly seen and why?
Rhyolitic magma is most commonly seen at convergent plate boundaries and infra-plate hotspots, becasue the magma MUST pass through the earths crust to reach the earth crust (where it absorbs silica).
What determines the shape of a volcano being formed as well as the explosiveness of its eruptions?
The viscosity.
What is the term for volcanoes produced by basaltic magma? Why?
Shield volcanoes - they are shaped like a warriors shield. The low viscosity of the magma allows for the formation of broad, gentle sloping volcanoes.
Describe the severity of eruptions from a shield volcanoes? Why?
Shield volcanoes have relatively mild eruptions. The low viscosity of the basaltic magma that forms these volcanoes allows gas to escape fairly easily, resulting in relatively mild eruptions.
What is the largest known volcano on earth? What type of volcano is this? Where is it?
Tami Massif, located in the Northwest Pacific Ocean (east of Japan). It is a shield volcano covering over 500 000 square kilometres.
What type of volcano is produced by Rhyolitic magma?
A Stratovolcano (composite volcano).
Describe the geographic features of a Stratovolcano and its eruption characteristics.
Because Stratovolcano’s are formed by Rhyolitic magma (high viscosity), the magma doesn’t flow very far before solidifying. Thus a Stratovolcano will have lava thats built up forming steep slopes. Rhyolitic magma also easily traps gas (because of high viscosity) causing pressure to build and build before releasing catastrophic eruptions.
When did the Krakatoa volcano erupt. What type of volcano is this?
In 1883 the Krakatoa volcano (Stratovolcano) erupted.
What volcano is famous for destroying the town of Pompeii and Herculaneum in 79 AD? What type of volcano is this?
The volcano Vesuvius erupted in 79 AD. This is a Stratovolcano, formed by Rhyolitic magma.
Which volcanoes have erupted catastrophically in modern times?
Mount Saint Helens and Mount Pinatubo
What is one of the intermediate types of volcanoes?
Because there is a gradient in the silica content and viscosity of Magma, there exists intermediate types of volcanoes. One type is the Cinder Cone Volcano.
What is the most famous Cinder Cone Volcano? When/where did this volcano develop? How high is it today?
Paricutin grew out of a corn field in Mexico in 1943. Eruptions continued for 9 years, built the cone to a height of 424 meters and produced lava flows that covered 25 kilometres.
Where is the volcano Kilauea? How long have its eruptions been ongoing?
In Hawaii. Eruptions have been happening since 1983. This volcano has destroyed around 200 homes, covered 125 square kilometres of land as well as 14 kilometres of highway.
What is considered the least hazardous volcanic process? Why?
Lava flows - because they’re usually not life threatening.
How is volcanic ash formed?
Volcanic ash is produced by explosive eruptions. When gas explodes out of magma, the magma is shattered and propelled into the air. It quickly solidifies forming shards of rock and glass. Therefore it is very heavy and abrasive.
How far can volcanic ash travel?
Thousands of kilometres.
How is volcanic ash hazardous?
1 - block solar radiation
2 - Destroys infrastructure and crops
3 - collapse roofs
4 - clog airplane engines
5 - causes breathing problems and suffocation to both humans and animals
What happened in April, 2010 in Iceland?
The eruption of Eyjafjallajokull severely affected air traffic control in Europe, costing them almost 3 billion dollars. It grounded passengers for a week as well.
What are pyroclastic flows?
Created by an explosive volcanic eruption, pyroclastic flows occur when ejected rock and ash move downslope at speeds up to 700km per hour. They are also extremely hot reaching hundreds of degrees Celsius.
Describe what happened during the eruption of mount Pelee
Mount Pelee, in the Caribbean, erupted in 1902 creating pyroclastic flows that buried the town of St. Pierre and killed 30 000 people.
What is a Lahar?
A lahar is one of the most dangerous features of a volcano. It is kind of like a volcanic debris flow and caused when melting snow (from an eruption) is mixed with lose volcanic ash and rock. This mixture overflows creeks and rivers that flow downslope and can be describes as liquid cement. Lahars are often hot and can cause burn injuries to their victims. They don’t require a large eruption to be triggered and will destroy everything in their path.
Describe the most deadly Lahar in Columbia.
In 1985, Nevado del Ruiz erupted in Columbia. It wasn’t a large eruption, but it melted the volcanoes summit glaciers causing a series of lahars that flowed down rivers killing several communities and 23 000 people.
Describe the eruption of Krakatau
Krakatau in Indonesia erupted in 1883, causing a large tsunami and killing more than 36 000 people.
What is the greatest impact that volcanoes have had throughout history?
Their release of gas into the atmosphere - causing implications to the earths climate.
What harmful gases are released from volcanic eruptions?
1 - carbon dioxide
2 - sulphur dioxide
How does the release of carbon dioxide from volcanic eruptions impact the earths climate?
Carbon dioxide is a greenhouse gas. Greenhouse gasses are essential for the earth because they absorb solar energy rather than reflect it. Therefore volcanoes are important for regulating the atmospheric temperature of the earth. However, if there is too much CO2 in the atmosphere, the temperature of the earth will rise causing climate change.
How does sulphur dioxide from a volcanic eruptions impact impact the earth?
Sulphur dioxide reacts with water vapour to create sulfuric acid which falls as acid rain. The high albedo of sulphuric acid can also cause a temporary cooling of the earths climate. This volcanic ash can sometimes cause a “volcanic winter”.
What were the consequences of the eruption of mount Pinatubo?
In the phillapeans, mount Pinatubo erupted, causing a volcanic winter the years following the eruption.
What are 5 things to remember is your travelling in avalanche country?
1 - get the gear
2 - get the training
3 - get the forecast
4 - get the picture
5 - get out of harms way
