GCSE Geography OCR B - Volcanoes

Mechanical layers of the Earth

Lithosphere - 0-100km, solid crust

Asthenosphere - 100-350km, not exactly solid

Mesosphere - 350-2900km, rigid

Outer Core - 2900-5100km, molten

Inner Core - 5100-6370km, solid, iron

Structure of Earth

Crust - outer layer, 0-100km

Mantle - middle layer, 100-2900km

Outer Core - 2900-5100km, 5000°c

Inner Core - centre, 5100-6378km, 3000°c

Convection Currents

Heat from the core rises to the top of the mantle

Magma heats up

Heated magma rises to the top of the mantle

Heated magma spreads to the sides

As magma cools down, it goes back through the mantle

Magma goes back down to the heat source

Crust moves in direction of magma

Oceanic Crust Vs Continental Crust

Oceanic Crust:

Heavier/Dense

Thin (6-10km)

Young (less than 200 million years)

Continental Crust:

Lighter/Less Dense

Thick (35-70km)

Old (over 1500 million years)

Proof of Continental Drift

Jigsaw Fit:

-Fossils and rocks of the same animal, found thousands of miles apart

-Continents look like they should fit together

-Rock types, layers and orders are the same, but thousands of miles apart

Palaeomagnetism:

-Magnetism of rocks will vary between north and south poles

-Changes magnetism every 250,000 years

-Strips of rock have different magnetisms

-New technology to find ridges on ocean floor

Seismic Waves:

-Monitoring stations monitor seismic waves bouncing off of things

Constructive Plate Boundary

-Occurs when two plates move away from each other

-Earthquakes and volcanoes

Destructive Plate Boundary

-Occurs when oceanic plate subducts the continental plate

-Earthquakes and Volcanoes

Conservative Plate Boundary

-Occurs when two plates slide past each other

-Earthquakes and Faulting

Collision Plate Boundary

-Occurs when two continental plates collide

-Earthquakes and Fold Mountains

Fissure Volcano

-A long, narrow volcano that forms at cracks and weak points in the earth's crust

-Fluid, basaltic lava, "pahoehoe", effusive

-Found on Constructive plate boundaries

-Gentle and persistent eruptions

Shield Volcanoes

-Gentle, sloping sides. Low and flat

-Fluid, basaltic lava, "pahoehoe", effusive

-Found on Constructive plate boundaries or hotspots

-Gentle and predictable eruptions

Composite Volcanoes

-A tall, cone-shaped mountain in which layers of lava alternate with layers of ash and other volcanic materials

-Viscous, sticky, high silica, lava, "aa", explosive

-Found on Destructive plate boundaries

-Explosive and unpredictable eruptions

Caldera Volcanoes

-Gigantic volcanic depression, much larger than a crater; happens when magma chamber empties and the volcano collapses in

-Viscous, sticky, high silica, lava, "aa", explosive

-Found on Hotspots

-Very explosive and unpredictable

Volcano States

Extinct - never erupts again

Dormant - not erupted in 2000 years

Active - erupted recently, will erupt again

Why do people live near volcanoes?

Tourism

Precious Minerals

Geothermal Energy

Prediction/Monitoring Available

Tradition

Wealth

Good Soils

Primary Effects

-Blast, release of gasses, steam. sudden release of pressure

-Pyroclastic material, fragments of lava and rock

-Pyroclastic flows, incinerates everything in its path

-Lava flows

-Tsunami and earthquake

Secondary Effects

-Cloud formation, rainfall, thunderstorms

-Landslides, mudflows, lahars

-Melting ice caps

-Tsunami