Distrbution of Volcanoes
Where are Volcanoes found?
Volcanoes are found in long narrow bands.
They can be found on land or sea
They are found on convergent and divergent plate boundaries.
However, some are found in the middle of plates. Volcanoes found here are formed from Hotspots.
The largest band of volcanoes is found around the Pacific plate, it's called the Pacific Ring of Fire.
Distribution of Earthquakes
Where are Earthquakes found?
Earthquakes are found in long narrow bands.
They are found on all three plate boundaries (conservative, divergent and convergent).
They can occur on land and sea.
The largest band runs around the Pacific Ocean, others bands include down the middle of the Atlantic Ocean and through Europe and Asia.
The most violent earthquakes are often at conservative boundaries.
Convergent Plate Boundary
The main features at a Convergent boundary are: Ocean trench, Volcanoes, Subduction zone, Earthquakes, Fold Mountains.
The processes at a Convergent boundary are: the denser oceanic plate sinks due to convection currents. The heat from the mantle and friction cause the plate to melt and earthquakes to occur along the subduction zone. The less dense magma rises due to pressure and escapes through cracks and fissures in the surface. As the two plates compress together fold mountains are formed.
Divergent Plate Boundary
The features at a Divergent boundary are: Volcano (volcanic island if ocean), new crust, mid-oceanic ridge or rift valley, earthquakes.
The processes at a Divergent boundary are: the two plates move away from each other due to convection currents. The less dense magma rises into the gap. New crust is formed. If this happens in the ocean and breaks the oceans surface a volcanic island will form (Iceland).
Conservative Plate Boundary
The features at a conservative boundary are:
No crust is created or destroyed so there are no new landforms.
There is no volcanic activity!
Why do people live in areas of Volcanic Activity?
Reasons for living by volcanoes: Volcanic soil is very fertile which provides good produce for locals, they can make good money from this so do not want to leave (eg Naples). These areas are often very attractive for tourists which can provide locals with a good income (eg Sicily). Can provide 'free' geothermal energy (eg Iceland). They are too poor and cannot afford to move or they want to stay near their family and friends. Minerals can be found in volcanic rock and the money made from this is said to outweigh the risks. Or "It won't happen to me" attitude.
Why do people live in areas of Earthquake activity
Reasons for living in Earthquake zones: These areas are often very attractive to tourists and provide good income for locals (eg Turkey). The areas are often very beautiful so people want to live there despite the risk. There is improvements in Earthquake-proofing techniques in MIC/HIC's so people feel more safe in their homes (eg all new buildings in Japan are built earthquake-proof). The risk is considered acceptable because few people actually die from them. They cannot afford to move (eg Pakistan) or want to stay near family and friends.
Mercalli and Richter Scale
The Mercalli scale measures the damage done to humans, buildings and the environment. It is a scale that is very dependent on the observer so would be no good in an uninhabited area such as the desert. Also peoples opinions on what level the earthquake is may differ because it is an observational not scientific scale. The Richter scale is a logarithmic scale that measures the magnitude of the earthquake. Each level is ten times worse than the one below it and a seisometer is used to measure the violence of ground shaking. the scale is open-ended and is useful anywhere.
Focus and Epicentre of an Earthquake
The focus of an earthquake is the point under the Earth's surface where the earthquake originates.
The epicentre is directly above the focus where the shock waves first hit the Earth's surface. This is the area of greatest destruction.
The causes of the Earthquake in Izmit, Turkey
The Turkish landmass was being squeezed by three plates: the Eurasian plate moving South, the African plate moving North and the Arabian plate moving West.
The pressure from these plate movements caused several faults which included the North Anatolian Fault.
The Arabian plate moving westwards meant the North Anatolian fault experienced a lot of earthquakes. It is a conservative margin and the earthquakes were often severe.
Izmit lies on the North Anatolian Fault.
To make matters worse, the ground under Izmit is very soft clay and loose sand which moves a lot more than solid rock. This is what caused the collapse of a lot of buildings.
Effects of the Earthquake in Izmit, Turkey
18000 people died and 300000 were injured, the main cause of this was because the buildings were poorly designed and collapsed easily. 65000 buildings collapesed in Yalova alone. Also more people died because the earthquake happened in the early hours of the morning, 3.02am. The casualties were made worse because the road in Golchuk had a solid jam of cars meaning rescue workers could not get to victims. Also all the beds in the hospital in Gebze ran out therefore the injured suffered even more, some unnecessarily died. People that suffered from breathing illnesses were affected because the oil refinery in Tupras caught fire and 700000 tonnes of oil burnt which created a lot of air pollution. Many residents suffered from diarrhoea because a PVC factory leaked, a toxic waste dump cracked and a raw sewage escaped escaped into nearby water systems which contaminated the water. It was thought that cholera would break out. This also meant many fish and animals died. Local ecology suffered greatly. Two years after the earthquake 200000 were still living in pre-fabricated huts because they had all lost their homes and they had not yet been rebuilt. A final effect was the land around the Sea of Marmara was claimed back by the Sea which meant even more homes were lost.