Earth Structure Flashcards
What are convection currents and where do they occur?
They are circulation currents of heat in the mantle area
What are the main differences between oceanic and continental crust?
Oceanic crust - less than 200million years old
Continental crust - range from 1500million to 3.8 billion years
Oceanic density - 3g/cm3 : continental density - 2.7g/cm3
Oceanic crust is renewable and can be destroyed, continental cannot
O depth - 6-10km C depth - 70km
What is a constructive boundary?
This is when two plates move apart and magma rises from the mantle to fill the gap. The magma eventually cools and and new crust is formed. Volcanoes are a feature found at this type of margin.
What is a destructive boundary?
This is when 2 plates move towards eachother. The oceanic plate is denser and sinks under the continental plate and is destroyed. As a result deep ocean trenches are formed and volcanoes occur at the surface. Sometimes pressure builds as the plates move against eachother which can cause earthquakes.
What are collision boundaries?
When two continental plates move towards eachother. As neither can be destroyed, the earths surface buckles upwards and fold mountains are formed.
Conservative boundary
At these boundaries, the plates move sideways past eachother. Crust is neither created or destroyed but the plates can stick. This sometimes causes earthquakes after a build up of pressure.
Why do the continental plates move?
Convection currents.
How are fold mountains created?
1- rivers carries sediment to ancient seas 2- sediment was deposited at the bottom of seas in huge depressions called geosynclines 3- the sediment was compressed over millions of years to form sedimentary rocks 4- as two plates move towards eachother they push the layers of sediment up into folds
What is an anticline? What is a syncline?
Anticline - an upfold
Syncline - a downfold
When do overfolds occur?
When there is more pressure from one direction which causes it to fold over itself
Where can fold mountains be formed?
At destructive or collisional plate boundaries
What is the theory of continental drift?
The gradual movement of Earths continents separating over millions of years.
What is the evidence that supports the theory of continental drift?
Fossils found at the edges of South America and South Africa meaning they were possibly joint together at some point in time.
What are the main sources of income for people living in the Himalayas?
Tourism - eg: shops, hotels, tour guides (Sherpas)
Farming - 76% of people who live in Nepal work in farming
What is micro hydro electric power in the Himalayas?
They generate electricity through using steep hill rivers and streams. It is clean and renewable
