Restless Earth Flashcards
What is the crust?
The outer layer of the earth.
What is a plate?
A section of the earths crust.
What is a plate margin?
The boundary where two plates meet.
What is the mantle
The dense, mostly solid layer of the earth between the outer core and the crust
What are convection currents?
The circular currents of heat in the mantle
What are the characteristics of the oceanic crust
Newer -most less than 2 million years old
Denser
Can sink
Can be renewed and destroyed
What are the characteristics of the continental crust
Older- most over 1500 million years old
Less dense
Cannot sink
Cannot be renewed or destroyed
What is the structure of the earth?
Crust - outer
Mantle
Outer core
Inner core - inner
What is a destructive plate margin?
- 2 plates moving towards each other
- 1 plate slides under the other (oceanic under continental)
- Volcanoes and earthquakes can occur*
What is a constructive plate margin?
- 2 plates moving apart
* magma forces its way through cracks to form volcanoes*
What is a conservative plate margin?
- 2 plates slide alongside each other (same or opposite direction)
- sliding alongside causes pressure to be built up causing earthquakes*
What is a collision plate margin?
- 2 of the same type of plate move towards each other
* fold mountains*
Characteristics of composite volcanoes
- Steep slope, narrow base
- Eruptions infrequent and often violent
- Often have secondary cones made of lava and ash
Characteristics of shield volcanoes
- Wide base, gentle slopes
- Low rounded peak
- Layers made of running lava and little ash
- Eruptions frequent but non violent
What are fold mountains?
Large mountain ranges where rock layers have been crumpled as they have been forced together. They have anticlines and synclines
What are ocean trenches?
Deep sections of the ocean where an oceanic plate is subducting below a continental plate
What is a composite volcano?
Steep sided volcano that is made up of a variety of materials, such as lava and ash
What is a shield volcano?
Broad volcano made mostly of lava
Volcano distribution notes
- Spread relates closely to plate margins (especially the ring of fire around the Pacific plate)
- Occasionally found away from plate boundaries at cracks in the crust
Monitoring volcanoes
1) Monitoring earthquake activity; when a volcano is about to erupt, magma rises beneath it causing rocks to crack and break, causing earthquakes that can be measured with a seismometer
2) Tiltmeters on the ground; when magma rises, it cause slight changes in the tilt of the ground. This can also be measured by GPS to detec minute changes or laser beams to measure changes of distances on a volcano
3) Digital cameras to record small eruptions or landslides; the sea re caused by rising magma, and this is safe because it is controlled from a distance
4) Monitoring gases released; changes in concentrations of gases like sulphur dioxide can indicate a potential eruption
Process of a super volcano eruption
1) Magma rises through cracks in the crust to form a magma basin below the surface and the pressure causes a bulge several km wide to form.
2) The bulge cracks, creating vents for lava to escape. As it erupts from the vents, it causes earthquakes and plumes of ash and rock
3) As the bulge empties, its support decreases until it collapses and sends out more lava
4) When the eruption has finished, there’s a big crater (caldera) left behind.
Consequences of a super volcano eruption
- It will throw out thousands of cubic km of rock, ash and lava, potentially blocking out the daylight over continents and triggering mini ice ages as less heat can reach the earth
- A cloud of ash and superheated gas flows at high speed, destroying everything in its path
- Ash will settle over hundreds of km squared
Information about the LAST super volcano eruption
- Erupted 74,000 years ago in Tobai, Indonesia, producing 3000km cubed of ash
- 15cm of ash fell and global temperatures decreased by 3-5°C
