A - Tectonic Hazards Flashcards
What is the Earth’s crust divided into?
The Earth’s crust is divided into tectonic plates that float on the mantle (a layer of semi-molten rock).
2 types of crust
Continental and oceanic
Describe continental crust
Crust is thicker (30-50km) and less dense
Describe oceanic crust
Crust in thinner (5-10km) and more dense
How do plates move?
Plates move due to convection currents in the mantle.
What are the places called where plates meet?
The places where plates meet are called plate margins or plate boundaries.
3 types of plate margins
Destructive margins, constructive margins, conservative margins
Define destructive margin
Where 2 plates are moving towards each other
○ Where an oceanic plate meets a continental plate - the denser oceanic plate is subducted and destroyed, creating gas-rich magma, volcanoes and ocean trenches occur
○ Where 2 continental plates meet, the ground is folded upwards, creating fold mountains
Define constructive margin
Where 2 plates are moving away from each other
○ Magma rises from the mantle to fill the gap and cools, creating new crust
Define conservative margin
Where 2 plates are moving sideways past each other / moving in the same direction at different speeds
○ Crust is not created or destroyed
Where are earthquakes globally distributed?
Earthquakes are found along all types of plate margins.
They mostly occur along boundaries between major tectonic plates.
A few occur in the middle of plates.
Where are volcanoes globally distributed?
Volcanoes only occur at constructive and destructive plate margins.
They also occur at hot spots (parts of the mantle that are really hot) such as Hawaii in the Pacific Ocean.
A lot of volcanic activity occurs in the ‘ring of fire’ - a group of volcanoes located along the plate margin of the Pacific plate.
How do volcanoes form at constructive plate margins?
The magma rises up into the gap created by the plates moving apart, forming a volcano.
How do earthquakes form at constructive plate margins?
Tension builds along the cracks in the plates as they move away from each other, forming an earthquake.
How do volcanoes form at destructive plate margins?
The denser oceanic plate moves down into the mantle, where it melts. A pool of magma forms, which then rises through cracks in the crust called vents. The lava erupts, forming a volcano.