Global Hazards Flashcards
(28 cards)
What is the depth range of oceanic crust?
6-8 km deep, Oceanic crust is thinner but denser than continental crust.
How does oceanic crust behave at plate boundaries?
Subducts under continental crust
This occurs due to its higher density.
What is the average depth of continental crust?
30 km deep, Continental crust is thicker but less dense than oceanic crust.
Continental crust is thicker but less dense than oceanic crust.
What happens at constructive plate boundaries?
2 plates moving apart
Magma rises through gap
Magma cools and solidifies creating shield volcanoes
e.g. mid Atlantic ridge - eurasian and north american
Example: Iceland has volcanoes formed at these boundaries.
What characterizes destructive plate boundaries?
Oceanic + continental crust moving together
Oceanic crust subducts beneath continental crust
Creates ocean trenches, earthquakes and composite volcanoes
Earthquakes occur due to friction during subduction.
e.g. ring of fire - nazca and south american
Earthquakes occur due to friction during subduction.
What occurs at collision plate boundaries?
2 continental plates push against each other
Force each other upwards
Causes earthquakes and fold mountains
e.g. himalayas - eurasian and indian
Example: Himalayas formed by this process.
What is the nature of conservative plate boundaries?
Plates moving alongside each other
Friction builds up to form earthquakes
No crust is created or destroyed at these boundaries.
e.g. san andreas fault - pacific and north american
No crust is created or destroyed at these boundaries.
What are hotspots?
Plumes of magma rise through mantle to the crust
Creates volcanic islands away from plate boundaries
Example: Hawaii is formed from a hotspot.
What are the characteristics of shallow focus earthquakes?
Depth less than 70 km
Common frequency
Magnitude 1-5
More damage closer to surface because energy from shallow focus earthquakes is better transmitted.
Energy from shallow focus earthquakes is better transmitted.
What are the characteristics of deep focus earthquakes?
Depth greater than 70 km
Rare frequency
Magnitude 6-8
Less damage compared to shallow focus
Occur at destructive plate boundaries
Occur at destructive plate boundaries.
What does the Richter Scale measure?
Magnitude of an earthquake
Scale from 1-10
Scale typically ranges from 2-8.
What does the Mercalli scale measure?
Damage caused by an earthquake
Scale from 1-12
Scale ranges from 1-12.
What are composite volcanoes characterized by?
Steeper and smaller slopes
More viscous, cooler lava
Dangerous eruptions due to gas trapping
Eruptions are less frequent but can be more explosive.
What are shield volcanoes characterized by?
Gentle slopes, wider base
More fluid, hotter lava
More frequent eruptions
Eruptions are less dangerous due to lack of gas trapping.
What are top-down building adaptations?
Building codes that may not always be enforced
Shatter-proof glass
Reinforced stell core
Rubber base isolators - absorb shockwave force
These adaptations are meant to enhance structural safety during earthquakes.
What are bottom-up building adaptations?
Retrofitting existing structures
Securing furniture to prevent injuries
Cross-bracing for stability
These adaptations are typically more cost-effective.
What is the Hadley Cell?
Between 0 and 30 degrees latitude N and S
Low pressure at equator
High pressure at 30 degrees
It describes the circulation of air due to solar radiation.
What is the Coriolis effect?
Earth’s rotation causes storm rotation
Anticlockwise in Northern Hemisphere
Clockwise in Southern Hemisphere
Influences weather patterns and storm direction.
What are the effects of El Niño?
Weakens trade winds
Less precipitation in Western Pacific
Higher pressure conditions
Can lead to droughts in Australia due to less frontal rainfall and increased precipitation in South America
Results in cooler surface water temperatures.
What are the effects of La Niña?
Increases strength of trade winds
More warm water in Western Pacific
Cold water rises in Eastern Pacific
Can lead to droughts in South America and increased precipitation in Western Pacific
Can lead to droughts in South America and increased precipitation in Western Pacific.
What causes flash floods?
Heavy rainfall
Saturated ground
Small, round basin
Steep valley sides
Lack of vegetation
Impermeable rock
Water cannot infiltrate or drain away fast enough.
How do tropical storms form + move inland?
5-20 degrees latitude, tropics, formed over water above 26.5 degrees or more, warm air rises on sides creating eye of storm, rising air each side with precipitation
Converging trade winds push storm inland, loses energy when over land
How has Hawaii island chain been formed?
As plate moves over hotspot, volcanic island are formed, when no longer over hotspot they are dormant and are eroded until submerged
What is the Ferrell cell?
30-60 degrees latitude, low pressure at 60, air rises and moves towards high pressure 30, cools and sinks then moves from high pressure to low pressure, back to 60
