Tectonics

Tectonics

1. Tectonic Plates

   • The earth is made of plates that constantly move due to convection currents in the mantle below.
     • Important plates:
       • Eurasion
       • African
       • Pacific
       • North American
       • Indo-Australian
       • Nazcan
       • South American
       • Antarctic
   • Destructive Margin
     • A destructive margin is where two plates are moving towards each other.
       • Eg. Nazca's Ring of Fire
     • When an oceanic plate meets a continental plate, the oceanic plate subducts into the mantle.
       • This often creates volcanoes and oceanic trenches.
     • When a continental plate meets another continental plate, they collide but no crust is destroyed.
       • Fold mountains are often formed.
     • Usually form composite volcanoes.
   • Constructive Margin
     • Where two plates are moving away from each other.
       • Eg. Iceland
     • Magma rises from the mantle and cools, forming new crust.
     • Usually form shield volcanoes.
   • Conservative Margin
     • Plates may be moving in opposite directions, past each other.
     • Or in the same direction, but at different speeds.
     • Eg. the North American plate and the Pacific plate.
     • They may get stuck, but the build up of pressure may cause a release in the shape of an earthquake.
     • Crust is neither made or destroyed.

2. Fold Mountains and Ocean Trenches

   • The Alps
     • A Fold Mountain Range
       • Central Europe - Austria, France, Italy, Germany, Switzerland.
       • Formed around 30 million years ago between African and European plates.
       • Mount Blanc the highest peak, 4810m on French-Italian border.
       • Population around 12 million people
     • Uses
       • Farming
         • Steep upland areas to farm goats
         • Vineyards
       • HEP
         • Berne area in Switzerland - gets 60% of electricity from HEP
       • Mining
         • Silver, Gold, Iron ore, Salt & Copper
         • Declined due to cheaper foreign sources.
       • Forestry
         • Scots Pine, resilient to munching goats.
         • Trees logged for furniture, etc.
       • Tourism
         • 100 million tourists per year
         • 70% of tourists in the winter.
         • New villages built, like Tignes in France
         • Ski runs, lifts, cable cars, holiday chalets and restaurants.
     • Adaptations
       • Steep relief: goats and defence against avalanches.
       • Poor soils for animal grazing.
       • Limited communications: roads built (Brenner Pass) and tunnels cut (Lotschberg Base Tunnel)
   • Fold Mountains
     • Formed at a destructive plate margin.
       • The rocks built up between them are folded and forced upwards to form mountains.
         • Two continental plates collide: the Himalayas.
         • A continental and an oceanic plate collide: the Andes in South America.
     • Fold mountains are often high rocky mountains with steep slopes, snow and glaciers in higher parts and lakes in the valleys.
     • Uses
       • Farming
         • Higher parts no good for farming, used to graze animals.
         • Steep slopes terraced to grow crops
       • Mining
         • Lots of metal ores.
         • Zig-zag roads carved into sides.
       • Tourism
         • Spectacular scenery
         • Winter
           • Skiing
           • Snowboarding
           • Ice Climbing
         • Summer
           • Walking
         • Tunnels to make straight roads, improves communications.
       • Forestry
         • Good environment to grow some trees like conifers.
         • Grown on steep valley slopes.
         • Used for:
           • Fuel
           • Building materials
       • Hydro-electric Power
         • Steep sided mountains
         • High lakes
         • Good places for generating hydro-electric power.
   • Ocean Trenches
     • Formed at a destructive boundary between an oceanic plate and a continental plate.
     • Form some of the deepest parts of the ocean.
     • Near to fold mountains.

3. Volcanoes

   • Soufriere Hills Volcano, Monserat
     • Montserrat is a small island in the Caribbean Sea
     • The volcano erupted on the 25th of June, 1997
     • 4 to 5 million metres squared of rock was released
     • 19 people were killed
     • Cause
       • Montserrat above a destructive plate margin, Atlantic Plate forced below Caribbean plate.
         • Magma rose up through the weak points, forming a magma pool below.
           • The rock above the pool collapsed, opening a vent and causing the eruption.
     • Primary Impacts
       • Plynouth, the capital, buried under 12m of mud & ash.
       • Over 20 villages and two thirds of homes destroyed by pyroclastic flows.
       • Schools, hospital, airport and port destroyed.
       • 19 people died and 7 were injured.
       • Vegetation and farmland destroyed.
     • Secondary Impacts
       • Fires destroyed local gov. offices, police headquarters and petrol station.
       • Tourists stayed away, business destroyed.
       • 8000 of 12 000 inhabitants left since 1995.
       • Volcanic ash improved soil fertility.
       • Tourism on the island increasing as people comes to see the volcano.
     • Immediate Responses
       • People evacuated from the south to north.
       • Temporary infrastructure built, eg. roads and electricity supplies.
       • UK provided £17 million of emergency aid.
       • Local emergency services provided search units for rescue.
       • Shelters built to house evacuees.
     • Long Term Responses
       • Risk map created and an exclusion zone, south of island of limits due to volcanic activity.
       • UK provided £41 million to develop north with new docks, an airport and houses.
       • Montserrat Volcano Observatory set up to predict future eruptions.
   • Mount St Helens
     • About
       • Mount St Helens is in Washington State in USA.
       • It erupted at 8:32am on the 18th of May 1980.
       • An earthquake caused measuring 5.1 on the Richter scale.
     • Primary Impacts
       • Fifty seven people died.
       • Landslide north-east of the mountain wiped out all living things in a 27km distance.
       • 200 homes and 300km of road destroyed.
       • 60 000km squared of volcanic debris.
       • Wildlife killed (elk, deer, bears, birds, small mammals)
     • Secondary Impacts
       • Commercial flights cancelled for two weeks.
   • Composite Volcanoes
     • Made of ash and lava that's erupted, cooled and hardened into layers.
     • Formed at destructive plate boundaries
     • Usually has thick, slow lava.
     • Parasitic vents/secondary cones on sides of volcanoes
     • Give out gas, ash, acid rain, pyroclastic flows and lahar
     • Eg. Mount Fuji
   • Shield Volcanoes
     • Formed at constructive plate margins
     • Made up of lava
     • Runny lava that flows quickly and spreads over a wide area, forming a low, flat volcano.
     • Eg. Mauna Loa on the Hawaiian Islands.
   • Dome Volcanoes
     • Formed commonly on composite volcanoes.
     • Made of lava.
     • Thick, slow flowing lava the hardens quickly, forming a steep slope.
     • Eg. Mount Pelee in the Caribbean.

4. Supervolcanoes

   • Yellow Stone
   • About
     • Causes
       • Supervolcanoes form at destructive plate boundaries or hotspots.
       • 1) Magma rises up through the cracks in the crusts from a magma basin below, creating a bulge on the surface, several km wide.
         • 2) The bulge eventually cracks, creating vents for lava to erupt through, causing earthquakes and sending up ash and rock.
           • 3) The magma basin empties leaving the bulge to collapse, spewing out more lava.
             • 4) After a big crater is left, called a caldera, where the bulge collapsed. Sometimes they fill with water (e.g. Lake Toba).
     • Characteristics
       • Emit at least 1000km cubed of material.
       • They have a caldera instead of a crater like normal volcanoes.
       • They are flat.
   • Consequences
     • A supervolcano eruption will throw out thousands of cubic kilometres of rock, ash and lava, compared to a couple of cubic km from normal volcanoes.
     • A thick cloud of super-heated gas and ash will flow at a high speed, killing, burning and burying everything within tens of miles.
     • Ash will shoot kilometres into the air and block out sunlight over whole continents, triggering a mini ice age.
     • The ash will settle over hundreds of square kilometres, burying fields and buildings, whereas ash from normal volcanoes usually covers a couple of square km.

5. Earthquakes

   • L'aquila, Italy
     • About
       • Occured 6th of April, 2009
         • 6.3 on Richter Scale
           • A destructive margin
     • Preparation
       • Laws on construction, but some modern buildings weren't built to withstand earthquakes.
       • Civil Protection Department trains volunteers in rescue.
     • Primary Effects
       • Around 290 deaths, most from collapsed buildings.
       • Thousands of buildings damaged or destroyed.
       • Thousands of people made homeless.
       • A bridge collapsed resulted in a broken water pipe near Paganica.
     • Secondary Effects
       • Aftershocks caused more damage and stopped rescue efforts.
       • Fires in some buildings .
       • Broken water pipe near Paganica caused a landslide.
     • Immediate Response
       • Camps were set up for homeless people with water, food and medical care.
       • Ambulances, fire engines and army sent to rescue survivors.
       • Cranes and diggers used to remove rubble.
       • International teams with rescue dogs sent to look for survivors
       • Money provided by government to pay rent, gas and electricity bills were suspended.
     • Long Term Response
       • Italian Prime Minister promised to build new town to replace L'Aquila as the capital.
       • An investigation is going on to look into why modern buildings weren't built to withstand earthquakes.
   • Kashmir, Pakistan
     • About
       • Occured 8th of October, 2005
         • 7.6 on Richter Scale
           • Destructive Margin
     • Preperation
       • No disaster planning.
       • Buildings not designed to resist earthquakes
       • Communications were poor, few roads that were badly constructed.
     • Primary Effects
       • Around 80 000 deaths
       • Hundreds of thousands of people injured.
       • Villages and buildings destroyed.
       • 3 million people made homeless.
       • Water pipelines and electricity lines broken.
     • Secondary Effects
       • Diarrhoea and other diseases spread due to little clean water.
       • Landslides buried buildings and people, blocked access roads, cut off water and electricity supplies and telephone lines.
       • Freezing winter conditions caused more casualties and meant rescue and rebuilding was difficult.
     • Immediate Response
       • Help took a long time to reach people.
       • There was no equipment for rescue.
       • Tents, blankets and medical supplies were distributed within a month but not to all areas.
       • International aid and equipment such as helicopters and rescue dogs were brought in.
     • Long Term Response
       • Around 40 000 people relocated to new town.
       • Government money given to people whose home's have been destroyed to rebuild homes themselves.
       • Training provided to rebuild more buildings as earthquake resistant.
       • New health care centres set up in the area.
   • Causes
     • At destructive margins the tension builds up when one plate gets stuck as it's moving. The pressure released causes an earthquake.
     • At constructive margins the tension builds up along cracks within the plates as they move away from each other.
     • At conservative margins the tension builds up when the plates move against each other and get stuck, so the pressure released causes an earthquake.
   • Characteristics
     • When the pressure is released the plates jerk past each other sending out shockwaves, or vibrations.
     • The waves spread out from the focus, which is the point where the earthquake starts.
     • The epicentre is the point above the focus.
     • Primary waves are quite weak and cause the surface to move backwards and forwards.
     • Secondary waves come next at a right angle to the main waves.
   • Measurements
     • The Mercalli Scale
       • Measures effects of earthquakes.
       • Scale of 1 to 12.
       • Eyewitness observations, words or photos.
     • Richter Scale
       • Measures the amount of energy released, called the magnitude.
       • Magnitude measured with a seismometer, which moves with vibration of earth.
       • Major earthquakes above 5.
       • No upper limit and is logarithmic, 5 is ten times more powerful than 4.

6. Tsunamies

   • Indian Ocean