Tectonic Hazards Flashcards

Flashcards based on Edexcel GCSE Geography B lecture notes covering the structure of the earth, plate boundaries, impacts of tectonic hazards, and their management.

Inner core

About 1400km in diameter, a solid and dense layer composed of iron and nickel with temperatures of about 5000 - 6000°C.

Outer core

About 2100km thick, a semi-molten metal layer with temperatures between about 4000-6000°C.

Mantle

About 2900km thick, a semi-molten layer which is less dense than the outer core, split into the asthenosphere and lower mantle.

Lithosphere

The thickness varies, and is made up of two types of crust together with the rigid upper part of the mantle. The two types of crust are Oceanic and Continental.

Oceanic crust

Thinner (5-10km) but heavier and denser, composed mainly of basalt.

Continental crust

Thicker (25-100km) but older and less dense, composed mainly of granite.

Asthenosphere

Partially molten plastic-type layer which moves under high pressure and is between 35-250km.

Lower mantle

Solid and the largest of the Earth's layers (2900km).

Convection Currents

Heat rises from the Earth's core and creates these in the mantle which move the tectonic plates.

Slab pull theory

Plate movement is a result of the weight of the denser oceanic plates subducting and dragging the rest of the plate along.

Mantle plumes

Upwellings of superheated rock within the mantle that can lead to divergent plate boundaries or hot spots.

Plate boundary

The place where tectonic plates meet.

Divergent plate boundary

Plates are moving apart; the Mid-Atlantic Ridge is an example.

Convergent plate boundary

Plates are moving together; the boundary between the Nazca and South American plate is an example.

Collision Zone

Two continental plates collide, and the rock folds forming fold mountains; the Himalayas are an example.

Conservative boundary

Plates move past each other in opposite directions or in the same direction at different speeds; the San Andreas Fault is an example.

Hot spot

A tectonic plate passes over a plume of magma, forming a line of islands; Hawaii is an example.

Global earthquake distribution

Most occur along the Pacific 'Ring of Fire'.

Volcano distribution

Majority of active ones are located around the rim of the Pacific Ocean, called the 'Ring of Fire'.

Magma

A volcano is formed when this erupts onto the Earth's surface as lava through a vent in the Earth's crust.

Volcanic Explosivity Index (VEI)

The scale used to measure the magnitude of a volcanic eruption.

Composite (strato-volcanoes)

Steep-sided volcanoes with sticky (viscous) lava and more explosive eruptions, formed from alternating layers of ash and lava, and found on convergent plate boundaries.

Shield volcanoes

Gently sloping sides with runny/thin lava, less explosive eruptions, found on divergent plate boundaries or hot spots.

Active volcano

The volcano has recently erupted and is likely to erupt again.

Dormant volcano

Has erupted in the last 2000 years and may possibly erupt again.

Extinct volcano

Shows no evidence of eruption in historic times and there is no evidence of a magma reservoir.

Lava

When magma erupts to the surface it is known as this; it can be thin and runny or thick and slow moving.

Ash

Pulverised solid lava which measures less than 2mm in diameter, ejected into the atmosphere and can travel thousands of kilometres.

Pyroclastic flow

Fast moving, very hot clouds of poisonous gases mixed with ash.

Lahars

When volcanoes erupt snow and ice on the peak melts and combines with the ash creating fast moving mud flows.

Volcanic bombs

Fragments of molten rock which are ejected from the volcano. These are between 60mm and 5m in diameter.

Epicentre

The point on the Earth's surface directly above the focus of an earthquake.

Focus

The point at which the earthquake starts below the Earth's surface.

Magnitude

The amount of energy released by earthquakes, measured on the Moment Magnitude Scale.

Seismometers

Used to measure the magnitude of earthquakes.

Primary hazards

Direct result of the earthquake or eruption.

Secondary hazards

Occur as a result of the primary effects.

Tsunami

When an earthquake occurs beneath the sea bed this can lead to this.

Primary impacts of Mount Merapi eruption

Ash reached altitudes of18km. Ash fell up to 30km from the volcano damaging 200 hectares offorest and large areas of crops. Pyroclastic ow spread 3km

Secondary impacts of Mount Merapi eruption

The exclusion zone had to be extended. Food prices increased due to the destruction of crops and livestock. The airports were closed to ights due to the ash

Primary impacts of Cumbre Vieja eruption

Almost 1,500 houses were destroyed by the lava ow. Over 1,500 other buildings were destroyed. The lava ow cut across the coastal highway and covered 1000 hectares

Secondary impacts of Cumbre Vieja eruption

Airtra c was suspended on a number of occasions due to ash in the atmosphere. Over1000 people were evacuated afterthe eruption began . A further 5600 people were evacuated overthe nextfew weeks

Primary impacts of Nepal earthquake

Approximately 9000 deaths. Over 20,000 people injured. Electricity and water supplies cut. UNESCO world heritage sites destroyed as well as many temples

Secondary impacts of Nepal earthquake

Almost 3.5 million people were made homeless. O ces, shops and factories were destroyed meaning people were unable to make a living. Loss oftouristincome which Nepal is reliant on

Primary impacts of Italy earthquake

Severe damage to buildings. 80% of buildings in Amatrice old town were a ected. 296 people died

Secondary impacts of Italy earthquake

Landslides blocked the roads. Psychological e ects on the population. Tourism was negatively a ected

Seismograph

Installed in 1924, 9km from Mount Merapi

Tiltmeters

Used around the volcano to detect changes ground levels

Satellites

Used to detect lava dome growth, heat of rising magma