Chapter 1 Earthquakes, Volcanoes, Plate Tectonics Flashcards
(9 cards)
- Explain how evidence supports Plate Tectonic Theory
It helps by showing the different possible ways that back up Wegener’s’ theory. With evidence the theory is easily proven and strengthened. Examples are Jigsaw fit, Convection currents, Study of fossils, Geographic patterns and Palaeomagnetism.
- Explain why earthquakes and volcanoes are found along plate boundaries
The reason to why earthquakes and volcanoes are found next to plate boundaries is because at diverging plate boundaries, earthquakes occur as the plates pull away, push and slide past from each other. Volcanoes also form as magma rises upward from the underlying mantle along the gap between the two plates and as two plates collide with each other. We almost never see these volcanoes, because most of them are located on the sea floor.
- Explain how earthquakes and volcanoes occur at Destructive plate boundaries?
Due to the radio active decay in the inner core, that is giving the heat, two plates move towards each other as a result of the convection that are propelling the plates (e,g the Nazca and South American plate) The oceanic plate is more dense than the Continental plate, as a result the oceanic plate is forced down,(known as subduction) sinks below (as the oceanic plate is made from basalt and the continental plate is made from granite)
Huge amounts of friction and heat occurs at the subduction zone making plates jammed together and suddenly they are released causing an earthquake that is much more violent then constructive plate boundaries.
When the plate sinks into the mantle it melts to form magma. The pressure of the magma builds up beneath the Earth’s surface. The magma escapes through weaknesses in the rock and rises up through a composite volcano. The newly molten rock is lighter (less dense) then what surrounds it, so it will rise towards the surface and cause volcanoes on the earth’s surface. However the magma doesn’t always reach to the top of the volcano (caldera) as they are slow moving, thick and high in silica, and cool (solidify) much quicker The volcanic eruptions are often violent, with lots of steam, gas and ash.
- Explain how earthquakes and volcanoes occur at Constructive plate boundaries
Down at the earth’s core, radioactive decay, creates huge amount ps of heat, generating powerful convection currents that, slowly move two plates apart from each other, causing earthquakes to occur (e.g. the Eurasian and North American plate.) This is happening right now in the Atlantic Ocean, creating the Mid Atlantic ridge, which is 1000km at its widest and 2.5km at its tallest in length. As the two plates diverge, magma from the ,mantle (high pressure zone) moves to the crust (low pressure zone). As the magma moves through the crust, it forms shield volcanoes. It is made quiet flat because the magma is low in silica, so it is very runny and flows further and longer. This is called seafloor spreading. These submarine volcanoes are under the sea, hence given their names. They are not as violent as the convergent (destructive) plate boundaries.
- Explain the effects of the Montserrat volcano (including facts)
- The population declined. The population fell from 12k to 3k due to the risk.
- Over 20 villages and 2/3rds of the buildings were destroyed.
- An ageing population has been created as younger people did not see an economic future and have not returned.
- 19 people died and 7 injured
- The port and airport were destroyed
- Explain what physical factors caused the Haiti earthquake to be so destructive?
Physical factors:
The ficus had been extremely shallow and where the epicentre had been located. Focus had been 8km underground and the epicentre only 15km from the capital Port-au-Prince. Resulted with 100,000 buildings destroyed and 200,000 damaged. 220,000 people killed and 300,000 injured. Another physical factor was the extremely strong earthquake and where Haiti had been located. As it had been a 7 magnitude and Haiti was on a conservative fault (80% of schools destroyed and the prison, in Port-au-Prince broke)
- Explain the cause of a Tsunami?
Most tsunamis are caused by earthquakes at destructive plate boundaries. Here, an oceanic plate is subducted into the mantle beneath a continental plate. This movement causes friction, which in turn causes the plates to stick. Energy accumulates, like that of a compressed spring. When the energy exceeds the friction, the plates snaps back into position. This movement thrusts the water above causing a wave to form. The waves can travel large distances. When the waves reach shallower water the following happens:
the shallow water slows the waves
the height of the waves can increase by several metres
the waves get closer together
The Ring of Fire (Facts)
The Ring of Fire is a roughly 25,000-mile chain of volcanoes and seismically active sites that outline the Pacific Ocean.Also known as the Circum-Pacific Belt.
The plates are constantly sliding past, colliding into, or moving above or below each other. This movement results in deep ocean trenches, volcanic eruptions, and earthquake epicenters along the boundaries where the plates meet, called fault lines.About 90% of the world’s earthquakes. The Ring of Fire is also where an estimated 75% of the planet’s volcanoes are located.
- Explain what human factors caused the Haiti earthquake to be so destructive?
Lack of building codes
cheap concrete, lack of consolidation and no building codes.
Could build any way they liked and had weak houses.
The level of development.
Haiti is the 160th worst country in terms of corruption.
Shows how poor and undeveloped the country is and how the earthquake just made matter much worse.
Each person lives on 85p each day.
