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Flashcards in Global Hazards Deck (37):

What is the Earth's structure?

Inner core, outer core, mantle and crust


What are the two types of crust?

Oceanic crust and Continental crust


Describe the types of crust.

Oceanic- Younger. Under 200 million years old. Thinner and more dense.
Continental- Older. Up to 3.8 billion years old. Thicker but less dense.


What are the four kinds of plate boundary?

Destructive, Constructive, Conservative and Collision


Describe what happens at a destructive plate boundary.

An Oceanic plate and Continental plate are driven towards each other by convection currents in mantle. They meet, lock and pressure and energy builds. Eventually Oceanic plate jolts forward and is forced under the Continental plate. This movement causes earthquakes. The subducted crust melts and that magma rises up through the cracks to form volcanoes.


Describe what happens at a constructive plate boundary.

Two plates are pushed away from each other by convection currents ans as they move minor earthquakes occur. A gap is formed in the crust and magma rises up through the gap and erupts. The magma hardens on gaps edges forming oceanic ridges and on land rift valleys form.


Describe what happens at a constructive plate boundary.

Two plates move alongside each other (same or opposite direction). They meet, lock and pressure and energy builds. One plate jolts forward and causes an earthquake where the energy is released in seismic waves. These earthquakes can be very powerful.


Describe what happens at a collision plate boundary.

Two continental plates move towards each other. They meet, lock and energy an pressure build. One plate jolts forward causing an earthquake, releasing the energy in seismic waves. These earthquakes can be very powerful. The crust here is crumpled and folded due to pressure.


Explain why there is a convection current in the mantle.

The core heats the magma in the lower mantle which rises because hot materials are less dense. It nears the crust, cools down and sinks. When it sinks it drags or pulls the tectonic plates with it.


What are hotspots and how to they form?

They form away from plate boundaries, when a plate moves past a particularly hot part of the mantle. A super-heated plume of hot magma rises up and "punches" through weakness in the crust causing volcano eruption and islands to form. As the crust moves past the hotspot, new islands are formed in an island chain (archipelago).


What are the four types of volcano?

Composite, Shield, Caldera and Fissure


Describe a Composite Volcano.

Found at destructive boundaries. Magma is sticky and more viscous, so moves slowly. Explosive eruptions. aa lava is erupted. Steep sided, built with layers of ash and lava. Cone shaped.


Describe a Shield Volcano.

Found at constructive boundaries. Magma is runny and less viscous, so can travel far. Quiet eruptions. Pahoehoe lava is erupted. Gentle eruptions.


Describe a Caldera Volcano.

Formed when a volcano erupts so violently that the magma chamber empties and the crater collapses into itself. A new cone will eventually form as magma rises again.


Describe a Fissure Volcano.

Forms at constructive boundaries when plates separate to leave a rift. There is no cone to erupt from, but lava erupts along a linear crack in the crust.


Where do earthquakes occur?

All plate boundaries.


What the point on the surface directly above the focus called?

The epicentre.


The point in the crust where the plates jolt after locking is where the EQ begins. What is this called?

The Focus


What are the first seismic waves to arrive called?

P Waves (Don't normally cause much damage)


What are the second waves to arrive called?

S Waves (Damaging waves)


What are some Primary Impacts of an earthquake?

Ground shaking. Collapsing Buildings. Death most likely from collapsed roofs and buildings. Snapped water, gas and electricity pipes or cables.


What are some secondary impacts of an earthquake?

Tsunamis. Liquefaction. Homelessness. Looting. Bereavement and grief


How can you reduce the damage from an earthquake?

Mitigation through technology. Building design. Early warning systems.


How can building design help reduce damage from an earthquake?

Tunes mass damper or pendulum. Floating foundations.


How does shake alert work?

Users have an app on their smart phone which tells SHAKEALERT their location (GPS). SHAKEALERT identifies an earthquake from the P WAVES, it calculates how much the ground will shake from these P WAVES and also the following S WAVES at locations across the country. It sends warnings, with the warning time ranging from a few seconds to a few tens of seconds, about the strength of both waves. SHAKEALERT can give enough time to slow trains, to prevent cars from entering bridges and tunnels, to move away from dangerous machines or to take cover under a desk. Taking such actions before shaking starts can reduce damage, injuries and deaths.


Describe Low Air Pressure

Hot air rises, cools, condenses and forms clouds and rain


Describe High Air Pressure

Cold air sinks and therefore can’t condense to form clouds or rain


Where is precipitation highest?

Low Pressure areas such as rainforests near the equator


Where is temperature highest?

Around the equator and also very high at 30* N and S due to high pressure (no clouds to block out the sun)


What is wind and where is it windiest?

Wind is air moving from higher to low pressure. So places with higher pressure difference have more wind


How warm does the sea need to be to form tropical storms?

At least 27*C


What causes the storm to spin?

The Coriolis Force


Which part of the storm has the heaviest rains and strongest winds?

The eye wall


What wind speed does a storm need to be classified as a hurricane/typhoon?

74 mph (category 1 on the Saffir-Simpson scale)


What is a drought?

A prolonged period of low rainfall leading to water shortages


What is a heatwave?

A long period where temperatures are much higher than normal


What causes a heat wave?

Higher pressure systems (sinking air so no clouds or rainfall)