Tectonics

Página 1

Structure of the Earth.

EARTH'S STRUCTURE:

Inner Core --> Outer Core --> Mantle --> Crust.

The crust and the solid part of the mantle near the top is called the Lithosphere.

The inner core is solid, the outer core is liquid, the mantle is slowly moving semi-molten rock and the crust is solid.

TECTONIC PLATES:

The crust is divided up into tectonic plates made out of either:

Continental crust: thicker and less dense.

Oceanic crust: thinner and more dense.

The plates move due to the rocks in the mantle moving (via convection currents).

TYPES OF PLATE BOUNDARY:

Constructive: plates move away from each other; magma rises from the mantle and cools to fill the gap, creating new crust (Mid-Atlantic Ridge).

Conservative: plates move by each other so crust isn't created or destroyed (San Andreas Fault, North America).

Destructive (Two Continental Plates): plates collide but no crust is destroyed - no subduction (Alps, Europe).

Destructive (Oceanic + Continental Plate): plates collide and the denser oceanic plate is forced down into the mantle and destroyed - subduction (Andes, South America).

Página 2

Fold Mountains.

FOLD MOUNTAINS:

When plates collide and the sedimentary rock between them is folded (or compressed) and forced upwards to form mountains.

Occurs along destructive plate boundaries - can be either where a continental plate and an oceanic plate collide or where two continental plates collide.

Fold mountain areas have lots of high mountains with rocky and steep slopes; there's often snow and glaciers, and lakes between the valleys.

USES OF FOLD MOUNTAINS:

Farming: higher slopes are used to graze animals and lower slopes are used to grow crops.

Hydro-electric Power: the steep sides and high lakes mean fold mountains are ideal for HEP.

Mining: fold mountains are a major source of metal ores.

Forestry: good environment for growing certain types of trees (like conifers); used for fuel, building materials, paper and furniture.

Tourism: in winter people come for the skiing and in summer for walking in the scenery; tunnels have been drilled through to make straight, fast roads.

Página 3

Fold Mountains Case Study - The Alps.

BACKGROUND INFORMATION:

Location: Central Europe, stretching across many countries such as France, Italy and Switzerland.

Tallest Peak: Mont Blanc - 4810m tall.

Population: 12 million.

USES OF THE ALPS:

Farming: steep, high areas used to farm goats which provide milk, cheese and meat; sunnier slopes terraced to plant vineyards like Lavaux, Switzerland.

Forestry: Scots Pine planted over the slopes - wood used for chalets, carved to sell to tourists and sold as furniture.

Hydro-electric Power: electricity produced is used locally - the Berne area in Switzerland gets 60% of its electricity from HEP in the Alps.

Tourism: 100 million tourists visit the Alps each year - 70% of tourists visiting in winter for the skiing and snowboarding; in the summer tourists visit for walking, mountain biking and climbing. New villages have been built to cater for the sheer amount of tourists,such as Tignes, France.

HOW PEOPLE HAVE ADAPTED TO THE CONDITIONS:

Steep Slopes + Climate: goats farmed due to their ability to climb the mountains; trees and man-made defences used to protect against avalanches.

Poor Soil: animals grazed in high areas where crops can't grow.

Limited Communications and Transport: roads built at the bottom of mountains (like the Brenner Pass between Austria and Italy) susceptible to being blocked by avalanches and takes a long time to drive along - tunnels cut through the mountains to provide faster transport links (such as the Lotschberg Base Tunnel in Switzerland).

Página 4

Volcanoes.

FORMATION OF VOLCANOES:

Formed on destructive and constructive plate boundaries.

At destructive boundaries: the oceanic plate goes under the continental plate where it's melted and destroyed in the mantle --> a pool of magma forms --> magma rises through cracks in the crust called vents --> magma erupts, forming a volcano (also creates an ocean trench).

At constructive boundaries: the magma rises up into the gap created by plates moving apart, forming a volcano.

Some volcanoes also form on the mantle in particularly hot areas called hotspots (such as Hawaii).

COMPOSITE VOLCANOES:

Made up of ash and lava that's erupted and hardened into layers.

Lava has high viscosity (thick) and flows slowly, but is cooler - hardens quickly to form steep sided cone shape.

Lots of gas that causes explosive eruptions.

SHIELD VOLCANOES:

Made up of layers of lava.

Lava has low viscosity (runny) and flows quickly, but is hotter - spreads over a wide area to form a low, flat volcano.

Little gas that causes gentle eruptions.

HAZARDS OF VOLCANOES:

Lava flows - Sheild volcanoes.

Steep sides cause landslides.

Lahars - a mixture of mud and ash to form a volcanic mud flow.

Ash falls.

Explosions.

Pyroclastic flows - flow of very fast hot ash and rocks.

Climate change - ash and gas in the atmosphere.

However, people do live near volcanoes due to very fertile lands which is good for agriculture.

SCIENTISTS TRY TO PREDICT VOLCANOES:

Tiny earthquakes.

Escaping gas.

Changes in shape in the volcano (bulges).

Página 5

Volcano Case Study - Montserrat, Caribbean.

BACKGROUND INFORMATION:

Location and Date of Eruption: Soufriere Hills erupted on 25th June 1997.

Size of Eruption: 4-5 million m3 of rocks and gas released.

Cause: Montserrat is on a destructive plate boundary where magma rose up through weak points in the Hills, forming a pool of magma; the rock above the pool collapsed, opening a vent and causing an eruption.

PRIMARY EFFECTS:

The capital, Plymouth, was buried under 12m of mud and ash.

Over 20 villages were destroyed by pyroclastic flows.

Schools, hospitals, the airport, the port and farmland were destroyed.

19 people died.

SECONDARY EFFECTS:

Fires destroyed many buildings, such as police headquarters and the petrol station.

Tourists stayed away and the economy was disrupted.

Population declined - 8000 of the 12000 inhabitants have left since 1997.

However, volcanic ash improved soil fertility and tourism has once more improved as people come to see the volcano.

IMMEDIATE AND SHORT TERM RESPONSES:

People were evacuated from the south to the north of Montserrat.

Temporary infrastructure and shelters were built to house evacuees.

The UK provided £17 million of emergency aid (because Montserrat is part of the British Overseas Territory.

Local emergency services provided search and rescue for survivors.

LONG TERM RESPONSES:

An exclusion zone was set up; the south of the island is still off limits.

The UK has provided £41 million to develop the north of the island - new docks at Little Bay, an airport and housing have been built.

The Montserrat Volcano Observatory has been set up to try and predict future eruptions.

Página 6

Supervolcanoes.

FORMATION OF A SUPERVOLCANO:

Form at destructive plate boundaries or on hotspots (example of a supervolcano: Yellowstone, USA).

How they form at hotspots: magma rises from gaps in crust to form a magma basin --> the pressure of the basin causes a bulge on the Earth's surface --> bulge cracks, spewing lava --> magma basin empties --> bulge no longer supported, collapses --> after eruption's finished, a caldera is left (a big crater) where the bulge and magma basin was.

CHARACTERISTICS OF A SUPERVOLCANO:

Flat (normal volcanoes are mountains).

Covers a large area.

Have a caldera (normal volcanoes usually just have a crater).

EFFECTS OF AN ERUPTION:

Eruption would throw out rock, ash and lava.

A cloud of hot gas and ash will kill, burn and bury everything within 10 miles.

Ash would reach over 1000 miles, suffocating many and burying fields and buildings.

Ash would block out the sun for most of the Earth, triggering a mini ice age.

Página 7

Earthquakes.

LOCATION AND CAUSE:

Destructive Boundaries: tension builds as one plate gets stuck as it's moving past the other into the mantle.

Constructive Boundaries: tension builds along cracks in plates as they move away from each other.

Conservative Boundaries: tension builds up when plates sliding past each other get stuck.

Eventually the plates jerk past each other, releasing energy and sending out seismic (shock) waves.

The shock waves spread out from the focus - the point in the Earth where the rocks break and where the earthquake starts.

The epicentre is the point of the Earth's surface straight above the focus.

MEASUREMENT OF EARTHQUAKES:

The Richter Scale:

Measures the amount of energy released by an earthquake (this is called the magnitude).

Magnitude is measured with a seismometer - a machine with an arm that moves with the vibrations of the Earth.

Logarithmic - a magnitude 5 is 10x more powerful than a magnitude 4.

The Mercalli Scale:

Measures the effects of an earthquake by eye-witness accounts - based on observation.

Observations in the form of words or photos (a 12 on the scale is 'total destruction') - less scientific.

Página 8

Tsunami Case Study - Indian Ocean.

BACKGROUND INFORMATION:

Occurred on the 26th December 2004 off the Indonesian coast.

Magnitude 8.9 on a destructive plate boundary.

CAUSES:

The plate moving down into the mantle caused a rupture 600 miles long, displacing a huge amount of water.

Caused a tsunami 30m high.

EFFECTS:

Affected over 10 countries bordering the Indian Ocean such as Indonesia, Sri Lanka and even as far away as the East African Coast.

Over 225, 000 killed or missing.

1.7 million made homeless.

Infrastructure (water pipes and electricity lines) of many countries severely damaged.

5 million needed emergency aid.

Economic damage: fishermen lost livelihoods, tourist industry suffered.

Environmental damage: mangroves, coral reefs and forests destroyed.

SHORT TERM RESPONSES:

Aid promised by America and Britain, such as rescue teams to look for and rescue survivors.

Japan sent ships full of bottled water.

Hundreds of millions pledged by foreign governments and charities to give aid to survivors.

LONG TERM RESPONSES:

Billions given to help rebuilding of infrastructure such as harbours to restore fishermen's livelihoods.

Disaster management plans put in place; volunteers trained so local people know what to do if another tsunami occurs.

Tsunami warning system set up in the Indian Ocean since a major reason the tsunami was so devastating was because there was no warning that it was going to occur.