Module 6 Flashcards
Zones of earthquakes
1) Divergent boundaries (new crust formation, magma emergence)
2) Convergent boundaries (subduction, compression, heat, friction)
Divergent boundary
Linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts, which eventually become rift valleys.
Examples include:
Mid-Atlantic Ridge
East African Rift System
Convergent boundary
Where two or more lithospheric plates collide. One plate eventually slides beneath the other (subduction). The subduction zone can be defined by a plane where many earthquakes occur.
Examples include:
Pacific Ring of Fire
Himalayas
Transform boundary
Fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduction zone.
Examples include:
San Andreas Fault in California
Zones of effusive volcanic eruptions (mafic)
Oceanic hotspots + divergent boundaries.
Thermal plume heats crust, causing expansion, swelling, cracking, and fracturing
Zones of explosive volcanic eruptions (felsic)
Characteristics of a volcanic region
- Increased rainfall, by forcing moist air to rise and form clouds
- large areas of bare ground
- Soils are young and fertile
- biologically diverse with many habitats
Weather vs Climate
Weather: is what conditions of the atmosphere are over a short period of time
Climate: is how the atmosphere “behaves” over relatively long periods of time.
High and low pressure systems
High pressure region: Regions of sinking air are called highs
- Dense air is forced downwards
- Clear skies and fair weather
Low pressure region: Regions of rising air are called lows
- Air is dragged in and forced upwards
- Clouds, rain and strong winds often occur in these regions.
Hailstorms
Hail is precipitation that falls in the form of ice…
Depth of earthquake focus at convergent boundaries
Shallow/ deep focuses
1) Deep: up to 700km, occurs from friction of descending plate
2) Shallow: occurs from movement along fault lines (fold mountains) or rocks displacing when magma rises/falls
Depth of earthquake focus at divergent boundaries
Only shallow focus
Cause of earthquakes
Sudden slip on fault- when stress on edge overcomes friction, earthquake releases seismic waves
Earthquake hazard: Ground motion
Earth shakes from seismic waves, creates infrastructure destruction and fatalities.
Eg. Turkey earthquake October 30th 2020 → building collapse, “locals search for residents trapped in debris of collapsed building”
Earthquake hazard: Tsunamis
Displacement of sea floor displaces water above it, generating large waves
Eg. Indian Ocean earthquake (9.1-9.3 magnitude) created tsunami → epicentre off the west coast of Northern Sumatra → 227,898 dead
Volcanic Hazards: Ash eruptions
Impact:
Abrasive fine particles enter, lungs, irritates eyes.
Ash fall smothers plant, contaminate water accumulate on buildings, collapsing them.
Eg. Eruption of St Mount Helens, USA, 1980
Volcanic Hazards: Lava flows
Least dangerous of all volcanic hazards (adult can walk faster than lava flow)
Buries, crushes, burns anything in path, starts fires. Devastating impacts on communities
Eg. Lava flows from Hawaii’s Kilauea volcano
Volcanic hazard: Lahars
Most dangerous/ deadliest
Erodes life/objects in its path, taking anything with it- gains speed up to 60km/h or more
Many volcanic deposits are acidic and can affect soil and river systems for many years
Eg. Armero, Columbia 1985
→ 23,000 people killed by lahar
→ destroyed land
Volcanic hazard: Poisonous gas emissions
Sulfuric acid, hydrogen sulfide, hydrogen chloride and hydrogen bromide.
Damaged eyes & mucous membranes
Carbon dioxide = global warming
Sulfur dioxide = cooling + ozone destruction
Eg. Dying forest around Mammoth Mountain due to high concentrations of CO2 in soil
Magma in convergent volcanoes (composite, strato)
Rhyolitic→ Rhyolite when cooled
High in: silica, viscosity, gas content, explosiveness/
Low in: temp (650-800C)
Magma in divergent volcanoes (shield, flood basalt)
Basaltic→ Basalt when cooled
High in: temp (1000-1200C)
Low in: silica, viscosity, gas content, explosiveness/effusive
Hazard vs Disaster
Hazard: threat (natural or human) with POTENTIAL to cause loss of life, injury, socio-economic disruption or environmental degradation
Hazard → Disaster: geological event must affect humans and exceed the ability of society to cope with hazard.
Impacts of explosive volcanic eruptions
Atmosphere:
1. Acid rain
2. Sulfate aerosols reflect UV light (cools atmosphere)
Biosphere:
1. Pyroclastic flows, magma, lava kills life
2. Acidic streams/ rainfalls/ water supplies limit access for organisms
3. CO2 accumulates in low-lying area, asphyxiating animals
Impacts of effusive volcanic eruptions
Atmosphere:
1. SO2 = acid rain, air pollution
2. CO2 accumulates in low-lying areas
Biosphere
1. Acid rain = starvation
2. Ash/lava flow = life killed
3. Fertile soils
Effects of major volcanic eruption on changing climate
Cooling incurred, where temps. drop up to 1C due to SO2 in atmosphere which reflect UV rays
Warming rarely incurred even from release of CO2 (impact is not strong enough to change climate)
Mount Pinatubo
Philippines (15 June 1991)
Cause:
Philippine plate subducted under Eurasian plate = escaped magma at convergent boundary = erupted 3 craters off volcano’s north flank
Effect:
1. Cooling of 0.5°C from 20 million tons of SO2 in stratosphere
2. 847 humans killed (collapsing roofs, lahars disease in evacuation centres eg. measles)
3. Rice paddies + sugar-cane fields buried & burnt by lahars and ash
4. Unusable harvest = 650,000 people lost jobs
5. Water contamination → reduced water supply for animals and people
