Tectonics edexcel geography alevel

Lava

molten rock on the surface of the Earth

Magma

molten rock inside the earth

Basalt

cooled lava (volcanic rock)

Effusive

less explosive eruption

Viscous

thick liquid

Composite/strath volcano

steep sided volcano

Silica magma

more silica equals more viscous

Rhyolite

rock formed by most viscous lava (convergent)

Convergent versus divergent eruptions

are more explosive and thicker more viscous lava, divergent erupt more frequently

Phreatomagmatic

combination of water and lava (ice on the surface) that makes the eruptions more explosive and dangerous

Hotspot

viscous or effusive lava – low viscosity lava and effusive

Hypocentre

where the earthquake originates from and is below the epicentre the deeper the hypocentre the less hazardous (measured using the moment magnitude scale MMS)

Volcanic explosive index (VEI)

how much material comes out of a volcano

Tephra

volcanic ash, lava bombs (everything blown out of a volcano)

Lahars

volcanic mud flows

Pyroclastic flow

hot clouds of toxic gases that move at high speeds

Earthquake waves (seismic waves)

Two types – surface and body waves

Body waves

two types – primary (p) and secondary (s) waves

P waves

longitudinal waves, can move through solids and liquids, move faster through denser rock, move at the speed of sound (1450 m/s)

S waves

move side to side, only move through solids, move faster through denser rock, travel at 60% of P waves speed but are more damaging due to a higher amplitude

Shadow zones

they exist where they (the waves) are not received/reach

Surface waves

Love waves and Rayleigh waves

Rayleigh waves

surface of the ground moves up and down

Love waves

ground moves side to side

Seismic gap theory

based on the assumption that all parts of a fault will move eventually. So, an area of fault that hasn’t moved/had any seismic activity in a long time will be the next area for seismic activity to take place

The Mercalli scale

measures the amount of damage done by an earthquake, used when we didn’t have the technology.

The moment magnitude scale

Developed in the 1970’s, this is the new way we measure earthquakes, it is measured on the size of the energy released, this is a logarithmic scale e.g. a 2 is 10x worse than 1

Tectonic event

does not effect people in any way (natural tectonic hazard)

Tectonic hazard

when the tectonic event effects people (disrupts daily life routines)

A disaster

when there are over 500 deaths

Mega disaster

over 2,000 deaths, 20,000 people made homeless, the GDP of the country is reduced by at least 5% or dependence on aid from abroad a year or more after the event.

Case studies

Developed world – Christchurch, NW, 2011

Emerging economy – Palu City, Indonesia, 2018

Developing world – Haiti, 2010

Convection currents

driven by radioactive decay, move the crust around

Seismic hazards

earthquakes that are generated when rocks 70 km of the earths surface come under stress that they break and become displaced

Intraplate earthquake

they occur in the middle or interior of tectonic plates and are much rarer than boundary earthquakes

Volcanic hotspot

an area in the mantle from which heat rises as a hot thermal plume from deep in the earth

Tsunamis

under sea earthquakes, landslides, slumps and volcanic eruptions that generate waves with long wavelength, low amplitude and fast velocities

Oceanic fracture zone

belt of activity through the oceans and along the mid ocean ridges through Africa, the red Sea, the dead Sea

Continental fracture zone

a belt of activity along the mountain ranges from Spain through the Alps to the Middle East and the Himalayas

The Swiss cheese model

For understanding accidents and improving safety e.g. Haiti had lots of layers to its disasters where the ‘holes’ lined up.