Restless Earth

Structure

Inner core 1300km solid 5000°C

Outer core 2100km liquid iron 3000°C

Mantle 2800km semi-liquid 1600°C

Crust 5-70km thick solid divided into plates

Plates move because of convection currents in the mantle 

Oceanic - Mostly Basalt, less than 200million years old, dense, sinks, renewed and destroyed.

Continental - Mostly Granite, over 1500million years old, less dense, cannot sink, cannot be renewed.

Volcano - a vent through which lava, ash etc. is erupted (often, but not always cone-shaped).

Earthquake - a sudden ground movement.

Oceanic and continental plates collide. Denser oceanic crust subducts under less dense continental crust where it is melted and destroyed.  Melting of the subducting plates creates magma which is lighter than the mantle and therefore rises resulting in the formation of volcanoes. Subduction zone and oceanic trench are formed and continental crust crumbles to form Fold Mountains eg. Andes.

Explosive volcanoes on either side as trapped sea water turns to steam. Not much lava but gas, steam and ash. Strong earthquakes when plates move.

Composite Cone

Plates pulled apart. Lava erupts through gap that is opened up. New crust formed and sea floor grows larger. Undersea volcanoes form mid-ocean ridge eg North American and Eurasian Plate forming the Mid-Atlantic Ridge.

Earthquakes when plates move.

Shield Volcano

Plates move past each other. Plates lock from friction. Pressure builds up until coastal rock snaps along a fault. When the plates break apart the energy is sent through the earth as seismic waves in the form of an earthquake eg. San Andreas Fault with North American and Pacific Plates.

Powerful earthquakes. No volcanoes.

Continental plates collide, neither is dense enough to sink. Plates crumple to form Fold Mountains eg Indo-Australian and Eurasian Plate forming the Himalayas.

Powerful earthquakes. No volcanoes.

(Ocean Trenches)

(Forms at a destructive boundary, oceanic crust subducted under continental. Area where they meet is an ocean trench. Like undersea valleys.)

Formed along plate boundaries where two plates meet - collision 2 continental or destructive oceanic and continental. Sedimentary rock forced upwards when collideto form eg. The Andes 7000km down western side of South America.

Farming - Subsistence farmers(Bolivia) grow potatoes and crops. Terraces make land flat, retain water, limit downward movement of thin soil. Llamas carry materials for irrigation and buildings in inaccessible areas. Seasons move livestock.

Mining - Tin, nickel, silver. Gold-bearing rock loosened by daily dynamic blasts then extracted. Contaminates water, soil pollution. Jobs.

HEP - Steep slopes narrow valleys easily dammed. Weather variation, snow melts so more water in summer for electricity.

Tourism - natural attractions eg. volcanoes and glaciers. Lack of services. Travel companies get money. Overpopulated, destroyed with hotels.

Composite Cone - infrequent but violent eruptions of sticky lava with silica, steep slopes, narrow base, plugs, DESTRUCTIVE boundary.

Shield - Frequent eruptions of runny lava with less silica, gentle slopes, low rounded peak, CONSTRUCTIVE boundary.

Active - erupted in 2000 years and erupt again.

Dormant - erupted in past, not 2000 years.

Extinct - never erupt again. 

An occurence over which people have very little control which poses a threat to people's lives and possesions.

Pyroclastic Flow - cloud of gas and ash, 700°C, 200km/hr.

Lahar - ash rain melted ice, deadly river of mud.

Lava - river of molten rock, 800-1200°C

Ash fall - millions of tonnes of ash bury buildings, roads, crops

Climate - ash high in atmosphere reflects sunlight, cooling global temperatures.

Hazard - destroy buildings, life and property, ash and lava kill animals and crops, interrupts communications, tsunamis, lower temps and more rainfall.

Benefit -  fertile soils if carefully managed, igneous rock contains minerals eg. gold copper lead silver and is useful for building purposes, extinct provide defensive settlement sites, geysers and volcanoes are tourist attractions, geothermal power, sunsets.

Tiltmeters - monitor change in shape

Seismometres - measure earthquakes within volcano

Gas analysis - measure gas and monitor changes

GPS / Satellite Data - monitor in detail from space, thermal satellites monitor temperature change

NOT on plate boundaries; on hotspots with huge magma plumes.

Rising magma can't escape so large bulge appears, cracks in surface gas and ash erupt from magma chamber, mc collapses forming depresion (caldera)

1000x normal volcano. Huge depressions called calderas. 1000km² wiped out. 2000-3000km³ material.

Cut off power supplies, air lines closed, millions traped under ash fall, people killed, lahars, landslides across globe. 

Sudden ground movements resulting from vibrations caused by earth movements at plate boundries and at major fault lines.

Worst at Conservative and destructive because of friction.

Two plates at plate boundary cannot easily move past each other because of friction. They become locked. Friction causes pressure to build up. Suddenly pressure is released and plates jolt into new position causing seismic waves. Vibrations are called earthquake.

Focus - where rock moves in earth. Seismic waves - energy moving through rock from focus. Epicentre - directly above focus on earth's surface.