GCSE Geography OCR B

What is a natural hazard?

An extreme natural event or process that causes loss of life and/or extreme damage to property and creates severe disruptions to human activities

Give an example of a terrestrial natural hazard?

A flood or avalance

How do the tectonic plates move? Explain.

Heat from the core rises up through the mantel taking magma. The magma reaches the bottom of the crust and spreads out. As it spreads out, it will drag against the crust and due to friction, it will cause the plates to move. The magma then cools and sinks back down. This process causes the plates to move.

What kind of eruption occurs at constructive plate boundaries?

Gentle eruptions

Explain what happens at a constructive plate boundary?

Sometimes called a divergent plate margine. At this plate boundary, the plates move apart. Volcanoes are formed as magma wells up to fill the gap and eventually new crust is formed. There are earthquakes and gentle eruptions here

Explain what happens at a destructive plate boundary?

Occurs when oceanic and continental plates move together. The oceanic playe is forced under the less dense continental plate (subduction). Friction from subduction causes the melting of the oceanic plate and may trigger earthquakes. Magma rises up through the crust and erupts into the surface. The eruptions are violent.

What happens at a collision plate boundary?

Two continental plates collide. Neither plate is forced under the other so both are forced up forming fold mountains. There are only earthquakes here (no volcanoes)

What happens at a conservative plate boundary?

Sometimes called a transform plate margin. Occurs when two plates slide past eachother in opposite directions or in the same direction but at different speeds. Friction is eventually overcome and the plates slip past in a sudden movement. The shockwaves create earthquakes due to the release of energy.

Describe the properties of oceanic crust?

Denser than continental crust and covered in water

How do volcanoes occur?

Volcanoes occur when heat rises causing convection currents to move the tectonic plates. The oceanic plate subducts under the less dense continental plate. The friction of subduction causes pressure to build up and the melt the oceanic plate. The pressure is released through the volcano.

What is the earths crust made up of

Tectonic plates

What type of plate boundary do we find violent eruptions?

Destructive plate boundary

Why is the pacific ring of fire so tectonically active?

Because the pacific plate is located here which is the largest and densest plate. It also borders several other plates and there is lots of destructive margins which are known to produce violent eruptions and the most powerful earthquakes

What are the 3 main areas volcanoes occur?

Hotspots, constructive plate boundaries and destructive plate boundaries

Other than lava, what 4 other things can be ejected by a volcano?

Ash, gasses, volcanic bombs and pyroclastic flow.

What determines what is ejected by a volcano?

The type of rock/eruption

What are eruptions like at a volcanic hotspot?

Gentle oozing of lava

What is a volcanic hotspot and what does it form?

A volcanic hotspot is a place where the crust is particularly thin. Magma may be able to escape to the surface. Such places are called a hotspot. Shield volcanoes will be formed.

Lava + water =

Ash

What is an ash cloud?

A cloud of ash that is the result of the volcano ejecting tonns of ash into the air due to high pressure

What is a Lahar?

A secondary hazard of a volcano. It is a destructive mudflow on the slopes of a volcano. It is caused by ash from the volcano mixing with water and rocks

What is a pyroclastic flow?

A flow of hot gasses and hot rock that travels at 80kmph

Why might someone want to live near a volcano?

They do not have enough money to live elsewhere or move, they may like the location and wish tonstay there, they may like the beautiful scenery, good business (volcano can be a tourist attraction), lava gasses are rich in minerals, health spars containing minerals dissolved im hot warer cure various illnesses and fertile soils are beneficial to farmers.

How might we know a volcano ia going to erupt?

Seismic activities, increase in gasses (especially sulfur dioxide, animals behave/ act weirdly (panic), earthquakes, temperature around the volcank increases, movement/tilt in the volcanles crater

How can we detect/ monitor the temperature of a volcano?

Using thermal imaging cameras

How can we detect the levels of gasses released from the volcano

Take a gas sample

How is a tsunami formed?

The plates are stuck together for hundreds of years, building up pressure. Suddenly, the two plates slip. This motion causes one plate to move under the other (subduction). This sudden subduction creates a displacement in water. The water moves, filling the gaps. The earthquakes seismic waves caused by thr slipping of plates as well as the displacement of water causes the tsunami

What is an earthquake?

Stress in the rock causes in increase in pressure. Jagged rocks at the fault line give way and the rocks slip causing seismic waves. This is an earthquake

What is the epicenter?

The most affected spot directly above the focus on the crust

What is the focus?

The weakest point where the pressure is released (centre)

What is ment by the magnitude of the earthquake?

The strength of the earthquake

What is a plate boundary?

A location were two plates meet

Where do we get the most powerful earthquakes

Destructive margins mostly

Where do we get the most frequent earthquakes?

Conservative plate boundaries. Tjis is becausr the 2 plates grinding together have the same density

What happens to the power of the earthquake the deeper underground the earthquake is?

The strength of shaking from an earthquake diminishes with increasing distance from the earthquakes source. This means that the strength of shaking at the surface from an earthquake 500km deep is considerably less than of the same earthquake had occured at a depth of 20km

What does the mercali scale measure?

The intensity of an earthquake?

What are the 3 types of seismic waves?

Pwaves, swaves surface waves.

What does the richter scale measure?

The earthqakes magnitude and shows the power of am earthquake

What is liquifaction?

A phenomenon where the strength and stiffness of the soil is reduced by the earthqakes or other rapid learching. Water leeks from the ground due to pressure

What signs might indicate an earthquake could occur?

Seismic activity noticed, stress in rocks/fault line increasing, strange activities shown by animals in the area, charts showing previous earthquakes