T1.1.3: Earthqauke Hazards, Volcanoes And Secondary Impacts Flashcards
What are the main secondary impacts of earthquakes:
T - Tsunamis
F - Fire
F - Flooding
L - Liquifaction
L - Landslides
C - Contamination
How do EQ cause tsunamis?
- earthquake under the water occurs due to the build up of stress especially near conservative and convergent PB
- Can cause the plate to be thrusted up or in different directions. Can cause the water column to be displaced up (mega thrust)
- Drops down and ripples out as a wave (radiates) with small amplitudes
- When approaching land —> sea bed becomes more shallow
Causes wave shoaling - depth decrease —> causes energy to compress —> makes waves cyclical
- causes water to recede and then tsunami hits the land
How do earthquakes cause fires?
- can cause buildings and infrastructure to collapse causing fires
- can cause gas leakages causing fires
How do earthquakes cause flooding?
- Can cause dams to break causing floods
- Can damage river defences and destroy sea banks
- Can burst pipes
How do earthquakes cause landslides?
- Earthquakes on steep slopes with lots of stress and weight can become destabilised further
- causes base of land to crumble causing landslide
How do earthquakes cause liquifaction?
- In the ground, grains of soil exist with pores/ gaps between the grains
- Gaps fill with water over time
- Earthquake vibrations destroy soil structure —> destabilises grains causing water to collate
- Causes land to act like a liquid and flow due to the water underneath
- Causes buildings above surface to sink and infrastructure below to rise.
How do earthquakes cause contamination of water/ pipes?
- Can break/ destroy sewage pipes and water sources
- Causes contamination of these sources
What is a stratovolcano/ composite volcano?
- refers to a large, steel-sided volcano which has built up over time from lava flows from highly effusive eruptions.
- More cone-shaped
Shield volcano definiton
- refers to a large broad volcano with shallow slopes formed by eruptions with low-viscosity lava travelling and cooling along long distances.
What are the different types of volcanic lava and how many are there.
3
1. Basaltic
2. Andesitic
3. Rhyolitic
What are the features of Basaltic lava?
Temp: Hottest —> 1000-1200
Mineral composition: Low Silica (50%), High Iron and Magnesium
Gas content: Low —> 0.5-2%
Formed by: Melting of mantle minerals from upper mantle
Flow characteristics: Low viscosity, runny —> leads to gases escaping
Eruption energy: Gentle, not as explosive
Origin: hotspots, shield volcanoes
What are the characteristics of andesitic lava
Temp: 800-1000 Celsius
Mineral content: Intermediate (60%) silica, magnesium and iron. High HCL
Gas content: 3-4%
Formed by: Subducted plate melts and mixes with seawater
Flow characteristics: Slow —> traps more gases
Eruption energy: Violent, explosive
Origin: Composite volcanoes with cones, subduction zones
What are the characteristics of Rhyolitic Lava?
Temp: Coolest —> 650-800 Celsius
Mineral composition: High silica (70%), potassium, sodium. Low iron and magnesium
Gas content: 4-6%
Formed by: melting of mantle from Subducted plates
Flow: High viscosity —> thick and stiff
Eruption energy: Very violent
Origin: Supervolcanoes
Primary impacts of volcanic eruptions?
P - Pyroclastic flow
L - Lava flows
A - Ash/ tephra falling
G - Gas eruptions/ clouds
Secondary impacts of volcanic eruptions
J - Jokulhlaups
L - Lahars
Pyroclastic flow definition and formation
- refers to a mixture of dense, hot, rock, ash and gases
1. Column of lava, ash and gases are expelled out of a volcano
2. This column of lava, ash and gas lose momentum
3. Gravity pulls it down to the surface and it accelerates down the sides of a volcano.
Lava flow definition and formation
Lava flows: flows of travelling magma that are a risk from damaging infrastructure and human life
1. Magma with low density rises above surrounding rock
2. Pressure decreases closer to the surface so some gases escape making magma less viscous
3. Erupts at surface and travels as lava
Ash/ Tephra definition and formation
Tephra: the lightest ash emitted during a volcanic eruption
1. Tephra is emitted upwards and can reach the troposphere/ stratosphere
2. Jet streams and other atmospheric processes distribute it out
3. Some ash then falls with heavier, denser particles falling first
Gas eruptions definiton and formation
Gas eruptions: when gases trapped in magma are release during eruptions forming gas clouds
1. In the mantle, low density magma rises
2. As it rises, pressure begins to decrease
3. As it reaches the surface, gas expands as pressure decreases and can cause explosions.
Lahars definition and formation
Lahars: a mixture of lava with mud and water which flows down the volcano at fast rates.
1. Lava flow occurs out of a volcano
2. Mixes with a water source, melting ice or rainfall
3. Less viscous so travels fast and destructively
Jokulhlaups definition and formation
Jokulhlaups: floods caused as water and glacial ice is melted by the heat of an eruption
1. As magma rises and heat is released by a volcano
2. Glacial ice is melted into groundwater forming a lake
3. As the volume of water grows under ice, water then flows down carrying sediment and ice
4. This floods settlements and is deposited in low-lying areas
