Week 7, Volcanoes Flashcards
Volcanic Hazards
- ash falls
- pyroclastic flows
- lahars
- volcanic landslides
- volcanic tsunamis
- lava flows
- volcanic gases
How are ash falls hazardous?
Dust-sized ash forms clouds above volcanos and drifts with winds and falls to the ground.
This can cause acid rain, blanket wide areas, interrupt air traffic, cause breathing difficulty, and make agricultural land and water unusable, and/or damage buildings.
What are pyroclastic flows?
Hot ash flows, mass of material that acts like fluid.
Hot, high-speed avalanche of volcanic fragments suspended in gases.
Temperature up to 1000 degrees c.
Travels up to 150km/hour or more
Most destructive, destroys everything in its path.
How are pyroclastic flows created?
Dome collapse: ejected from crater when dome collapses
Overspilling crater rim
Direct blast: side of the mountain blasts out
Eruption column collapse: Pressure from eruption cannot support weight of column, so it collapses in on itself and flows down the mountain as a pyroclastic flow.
What are lahars?
Mud flows
Volcanic fragments suspended in water
Can be hot or cold
Speeds up to 90 km/hour
How are lahars created?
A lot of water is needed!
Steam escape volcano, it’s in the ash, comes down as condensation, causes mudflows.
Heavy rain
Water from glaciation or snow melts
How do volcanic landslides work?
Many volcanos, often strata, are built on successive layers of lava and ash, they are structurally weak and prone to landslides.
Also explosive eruptions and earthquakes can trigger landslides.
How do volcanic tsunamis occur?
Violent underwater eruption (not at mid ocean ridges).
Volcanic landslides into bodies of water
Caldera collapse: Observed Krakatoa 1883 eruption, the worst tsunami. The powerful explosion blew out huge amounts of material, caldera collapse occurs, and the mountain collapses in on itself, it sinks into the ocean and this displaces the water to the point of causing a tsunami.
What are the concerns that arise from lava flows?
They’re usually not a big concern as they are not immediately life threatening, they can cause structural damage.
2 different kinds of lava flows
Aa Lava: High viscosity, blocky and slow moving
Pohoehoe Lava: Low viscosity, fast flowing lava
How are volcanic gases dangerous?
A high concentration of CO2 can displace 02 at low elevations, which can lead to asphyxiation, as observed at Lake Nyos when the lake “burped”.
The majority of volcanism occurs at
spreading centres.
Why is Mt. Rainier considered the greatest threat to the cascades?
Height: 4400m, tallest volcano in cascades
Ice/snow cover= great lahar potential
Frequent earthquakes
Active hot springs weaken the mountain internally
Mt. Rainier is an inherently unstable mountain with high landslide and lahar hazards.
Mt. Shasta
- second tallest of cascade volcanos
- strata, internally weak, significant lahar potential
- particularly known for landslides
Mt. St. Helens hazards:
- landslide
- pyroclastic flow
- lahar
- tsunami (spirit lake)
- ash fall
