Tectonics Flashcards
Describe the distribution of earthquakes and volcanos.
The distribution of earthquakes and volcanos is uneven, with the majority happening at the indo-australian plate boundary and on the ‘Pacific Ring of Fire’. The distribution is made up of long narrow belts mostly across plate boundaries with a few exceptions known as ‘hotspots’ where the crust is particularly thin.
What are plate tectonics?
The earths crust is divided into plates which float on the Earth mantle, made of magma. The plates also move due to convection currents caused by decay of radioactive elements in the mantle. The collision or moving apart of these plates causes volcanos and pressures which cause earthquakes.
What are hotspots?
A place where a volcano occurs which is not on a plate boundary but are fixed places in the mantle where intense heat bursts through the crust and magma is released which could create a volcano if it rises above the ocean level. Hotspots also regularly create chains of volcanic islands as the plate moves over the spot, e.g. Hawaii.
What happens at a continental-oceanic convergent plate boundary? (Destructive)
The oceanic plate undergoes subduction underneath the continental plate as it is much denser, this causes a deep ocean trench to form. The friction caused by the two plates melts the oceanic plate to create magma and earthquakes occur in the subduction zone. The land then buckles to form fold mountains and the magma forces its way up to form a volcano. An example of this is the Nazca oceanic plate meeting the South American continental Plate to form the Andes mountains.
What happens at a continental-continental convergent plate boundary? (Destructive)
The two plates slowly collide and the crust rises, uplifts and folds to form mountains. Earthquakes occur at the meeting point and no volcanos are formed as the crust is not being melted and subducted. An example is the Indian and Eurasian plate colliding to form the Himalayas.
What happens at a oceanic-oceanic convergent plate boundary? (Destructive)
The less dense plate (Philippine plate) subducts as it is forced down and is melted 100km below sea level. This forms magma which forces up to form a volcano. Earthquakes occur where the volcano emerges which later forms islands such as the Ryuku Islands. The Philippine plate and the Eurasian plate are an example of this.
What happens at a constructive plate boundary? (Divergent)
These usually form under the ocean and the volcanos created form ocean ridges. The two plate move apart leaving a gap for magma to escape through. The magma creates a new crust and if the magma reaches the surface a volcano emerges. The Eurasian plate and North American Plate are separating to create the Mid-Atlantic ridge and form volcanic islands such as Surtsey.
What happens at a conservitive plate boundary? (Transform)
Here the plates move along side each other and no crust or landforms is created or destroyed. The site is an area of intense earthquake activity as the plates tend to stick together and jerk forwards creating shock waves. The San Andreas fault is a plate where the two plates (North American and Pacific plates) are both moving at different speeds.
What are the characteristics of the Mercalli scale?
A measurement of activity measured via eye-witness accounts on a scale of 1-12 (only whole numbers) and is subjective. The person has to be present at the site and the scale is based off of destruction caused by the earthquake.
What are the characteristics of the Richter scale?
A measurement of the magnitude of an earthquake using a seismograph which is measured on a scale of 1-9. The scale is objective, can be done from a separate location and is logarithmic.
What are the characteristics of the Epicentre?
This is on the earths surface, where the worst effects are felt and as a result where the worst destruction to buildings and infrastructure will happen.
What are the characteristics of the Focus?
This is a point below the earths surface where the build-up of pressure is released and shockwaves are sent out. The depth of the earthquake varies.
What are the economic reasons behind why people live in areas of volcanic activity?
Soil is fertile - Coffee grown on the slopes of volcanos in Columbia
Cheap geothermal energy os produced - Reykjavik in Iceland
What are the social reasons behind why people live in areas of volcanic activity?
Perception, people think there is little risk or the government will stop it - People refused to leave the evacuation zone of Mt St Helens eruption
Family and friends, people won’t move because of family connections - People live on the slopes of Mt Etna in Sicily
Poverty in LICS, people can’t afford to leave - Mt Merapi in Indonesia
What are the environmental reasons behind why people live in areas of volcanic activity?
The area is scenic, making house prices more expensive and creates a tourist industry - Mt Vesuvius in Pompeii, Italy has a great tourist industry which provides jobs.
