- Created by: naomi
- Created on: 12-03-12 21:10
What causes earthquakes and volcanoes?
There are three main parts:
- Core: Central part of the earth. Temperature and pressure is enormous. Inner Core solid. Outer Core semi-liquid.
- Mantle: made up of rocks. occupying over 80% of earth's volume. mainly solid, but upper mantel is a layer of semi-liquid molten rock (MAGMA). The magma is moved slowly underneath the crust by convection currents.
- Crust: outer layer of rock. Floats on mantle. Solid rock. Broken into several pieces+ smaller pieces; AKA plates. fit together like a jigsaw. Some move around 2cm a year. The theory that describes this is Plate Tectonics. The place where 2 plates meets is a Plate Boundary (where most earthquakes/ volcanoes occur).
There are two types of crust:
- Continental (Older/lighter/can't sink)
- Oceanic (newer, heavier/can sink/constantly being destroyed and replaced)
There are three types of plate boundaries
- Convergent (destructive): One plate collides with another. When Oceanic crust collides with continental crust, the oceanic crust is forced downwards into the mantel and destroyed; a subduction zone (found where the pacific plate meets the Eurasian plate). Where two plates made of continental crust collide they are pushed upwards forming fold mountains (Himalayas/Andes).
- Divergent (constructive): Plates are forced apart by movement of magma in the mantle- new crust is formed in between (Mid-Atlantic volcanic ridge).
- Transform (conservative): where two plates move horizontally past each other (San Andreas Fault).
When two plates collide or slide past each other, it creates an earthquake. This means they occur at destructive and conservative plate margins.
How do earthquakes happen?
- Two plates move towards each other
- One gets pushed under the other.
- If the plate gets stuck it causes strain in the surrounding rock.
- Sideways moving rocks can also get stuck
- When the tension is released, it produces strong shock waves ; aka seismic waves
- The shock waves spread out from the focus (like a ripple effect). The waves get weaker as they move away from the focus.
Epicentre = point on the earth's surface above the focus.
Focus = The point where the earthquake starts.
How are earthquakes measured?
The size or magnitude of an earthquake is measured using a seisometre. Earthquake vibrations are measured by a sensitive arm which moves up and down on a seismograph (like a heart monitor).
Readings from the seismograph are measured using the Rhichter Scale: a logarithmic scale (earthquake measuring 5 is 10 times more powerful than one measuring 4 and 100 times more powerful than one measuring 3). This determines the strength of an earthquake.
Most serious earthquakes range between 5 and 10 on the Richter scale.
Why live at risk of earthquakes?
The benefits outweigh the dangers
- Job opportunities
- Education is better
- Standard of living is better
- More medical facilities
Preparing for an earthquake
Earthquake proof buildings are being introduced in MEDC cities
For example, in San Francisco, the buildings sway with the shock from the earthquake resulting in less damage being caused to the buildings. This also means that less people are killed or injured.
Improve preparation- In many places prone to earthquakes people try to prepare themselves. In Japan, the 1st of September is disaster day; the anniversary of the Tokyo earthquake of 1923; 156,000 were killed. The day is a public holiday which earthquake drills are practised.
Emergency supplies- people should keep updating their emergency supplies to ready themselves for any shortages during a disaster.
The Great California ShakeOut is an annual statewide earthquake drill on the third thursday of october. Millions of people practice... DROP! COVER! HOLD ON!
Case Study: Earthquake MEDC
Location: California Date: 22nd December 2003 Magnitude: 6.5 Richter Scale
Epicentre: 60 kilometres south west of the infamous San Andreas fault, which forms the boundary between the Pacific and North American plates. The Pacific plate is pushing northwest along the San Andreas fault, creating forces which are pushing up the mountain range.
The plates which caused it: San Andreas fault - conservative plate margin. Pacific plate (6cm p/year) North American plate (1cm p/year).
Primary and Secondary effects: Toxic Sulphur fumes were released from the erupting sulphur springs which meant the roads had to be closed because sulphur fumes were being breathed in.
Short and long term responses: 911 call centre prioritized its calls to make those for the earthquake faster responses, and rescue teams dedicated almost exclusively to search.
Case Study: Earthquake LEDC
Location: Bam, Iran Date: 26th December 2003 Magnitude: 6.6 Richter Scale
Epicentre: Centered approximately 10km to the southwest of Bam, which borders the Dasht-e-Lut desert. Initial investigations suggest that the event occurred on the Bam fault, and was caused by northward motion of the Arabian plate against the Eurasian plate
The plates which caused it: Arabian plate, Asian plate - Conservative plate margins
Primary and Secondary effects: 26,721 confirmed dead, 30,000 injured, 75% of houses were destroyed, well over half the population were left homeless and needed emergency housing and supplies (which was almost impossible to provide for)
Short and long term responses: The USA offered help to Iran almost straight away and although Iran declined it at first, they later accepted it. Rescue squads and medical supplies were also sent over to Bam.
What is a Volcano?
A volcano = A cone shaped mountain formed by surface eruptions from magma chambers. Volcanoes are found at constructive and destructive plate margins.
At Destructive Margins:
- The oceanic trench moves down into the mantle, where it's melted and destroyed.
- A pool of magma forms
- The magma rises through cracks in the crust called vents
- The magma erupts onto the surface(lava) and forms a volcano.
At Constructive Margins:
- Magma rises up into the gaps caused by plate movement (plates moving apart)
The world's distribution of volcanoes shoes almost a perfect fit with tectonic plate margins. Each time there is a volcanic eruption, a new layer of lava is added to the surface of the volcano.
Types of Volcano
Composite Volcanoes e.g. Vesuvius, Mount Etna
- Lava is usually thick and flows slowly, it hardens quickly forming a steep sided symmetrical volcano.
- Made up of ash and lava in alternate layers, lava cools inside and next eruption there will be an explosion.
- Subsidiary cones and vents form
Acid Lava Volcanoes (Dome/Cinder Volcanoes) e.g. Mount Pelee
- Made of only lava - steep cone with narrow base
- Lava is thick and flows slowly, forming a steep sided volcano
- Eruptions are explosive
Shield Volcanoes e.g. Mount Loa on Hawaiian Islands
- Lava is runny and flows quickly and spreads over a wide area forming a low, flat volcano, made only of lava - frequent, non violent eruptions.
A super volcano is much bigger than a standard volcano, they erupt with massive volumes of material and develop over hotspots. e.g. Yellowstone National Park.
What makes a super volcano?
- Magma rises through cracks in the crust forming a large magma basin below the surface. The pressure of the magma causes a circular bulge on the surface.
- The bulge cracks creating vents for lava to escape through, lava erupts out of vents causing earthquakes and sending up gigantic plumes of ash and rock.
- As the magma basin empties the bulge is no longer supported so collapses.
- When the eruption finishes there is a big crater (caldera) left where the bulge collapsed, sometimes these get full with water to form a large lake. E.g. Lake Toba in Indonesia
Characteristics of a super volcano? Flat, cover a large area, have caldera.
Global Effects of a Super Volcano
The last known eruption was about 75,000 years ago.
- The dust in the atmosphere would cause there to be little sunlight reaching earth, leading to a 'volcanic winter' which would lower global temperatures, which could lead to a mini ice - age.
- A thick cloud of super-heated gas and ash would flow at a high speed from the volcano, burning, burying and killing everything in it's way.
- It would alter the landscape of hundreds, and maybe even thousands of kilometres due to the huge amounts of material it releases; much more than Mount St Helens in the USA which released 1km3 of material.
Effects of Volcanoes
Primary Effects (Immediate Impact)
- People die/ are injured
- Housing/buildings/businesses/farmland destroyed
- Communications disrupted/destroyed
- Public services disrupted
Secondary Effects (Medium and long term impact)
- Healthcare aren't able to access: causes more people to die
- Loss of income - homeless - no food: causes more to die
- Economic problems: cost of rebuilding
- Grief: family stress
- Water contamination: disease and death
Benefits of Volcanoes:Fertile soil, tourism for many reasons: hot springs, atmosphere and views, Industry: Minerals (Sulphur, borax, pumice), generating power and heating things (geothermal power)
Warning Signs of a Volcanic Eruption
- Small earthquakes
- Increased emission of steam and gases
- Visual signs of bulging around crater
In rich countries, volcanoes are closely monitored to increase the amount of time people have to act when a volcano erupts.
- Electronic tilt metres measure very small changes in the profile of mountains
- Crater Satellites are used to measure the infra-red radiation and look for changes in heat activity.
Volcano Case Study - Eyjafjallajokull (Icelandic V
Eyjafjallajokull is a relatively small volcano on the south coast of Iceland
- It erupted almost continuously for most of April and May 2010
- The eruption was a ‘grey’ or ‘dry’ eruption for most of the first stage, shooting
- Millions of tonnes of pumice and ash into the air.
- This ash column drifted over Europe.
- The second stage involved some lava flows.
- There was little wind in England at the time of the eruption due to the air being stable. Wind would have broken up the ash cloud.
- Air in an anticyclone moves clockwise: this has sucked the air towards us
- from the northwest – straight from Iceland.
Causes of the Eyjafjallajokull Eruption
- Iceland is on the Mid Atlantic ridge.
- Iceland is right on a constructive plate boundary where the Europe is moving away from North America.
- The eruption was caused by the shifting of the North American plate and the European plate away from each other, as they naturally do due to the convection currents under the Earth's mantle.
- As the plates grow apart, this creates small cracks in the earth's crust allowing magma to force itself towards the surface, creating a volcanic eruption.
- The volcano is on the south coast and the wind carried the ash south-east towards Europe: away from the most inhabited areas of Iceland.
- The people living in the rural areas ‘down wind’ of the volcano had to wear goggles and face masks as the ash was so thick.
- Visibility is down to a couple of metres.
- There was a serious risk to the local cattle farmers and local businesses were suffering.
- Hundreds of thousands of tourists were stranded overseas, unable to fly home.
- Tourists paid thousands of pounds to get home using alternative transport (taxi, hire car, coach, bus, ferry, train)
- Businesses lost money as their workers did not return to work.
- Airlines and associated businesses were losing about £200 million a day.
- Airlines could not resume schedule straight away as planes and crew were in the wrong locations.
Global Effects: On Kenya
- 20% of the Kenyan economy is based on the export of green vegetables (beans, sugar-snap peas and okra) and cut flowers to Europe.
- These are perishable goods and they are transported by plane to keep them fresh.
- No flights into Europe meant products returned unsold and destroyed.
- Over 1 million flower stalks were unsold in the first two days. (3,000 tonnes of flowers had to be destroyed overall).
- Floral exports made up 20% of Kenya's economy - completely shut down by Europe's flight ban.
- Over 50,000 farmers were temporarily unemployed as their beans and peas could not be sold.
- The ash cloud has cost the Kenyan economy millions of pounds during the flight ban.
Much of western Europe's air traffic was shut down for a while due to high levels of dust particles. The local Icelandic response was more geared towards taking photographs and clearing dust from cars.
Some help was offered in finding alternative ways of travel, making the unscheduled stay in airports less uncomfortable and, in some cases, finding temporary accommodation for stranded passengers in hotels. As most the population of the world weren't in the least inconvenienced, nothing was done to help them as nothing was required.
The Formation of Fold Mountains
Fold mountains occur near convergent or compressional plate boundaries. Examples of fold mountains include the Alps, Rockies, Andes and Himalayas.
The formation of fold mountains
- Where an area of sea separates two plates, sediments settle on the sea floor in depressions called geosynclines. These sediments gradually become compressed into sedimentary rock.
- When the two plates move towards each other again, the layers of sedimentary rock on the sea floor become crumpled and folded.
- Eventually the sedimentary rock appears above sea level as a range of fold mountains.
Where the rocks are folded upwards, they are called anticlines. Where the rocks are folded downwards, they are called synclines. Severely folded and faulted rocks are called nappes.
Deep sections of the ocean, usually where an oceanic plate is sinking below a continental plate.
Characteristics of the Alps (Fold Mountains)
- High mountain ranges, eg Mont Blanc, which is 4,810 m above sea level.
- Glaciated valleys, eg the Rhone Valley.
- Pyramidal peaks, eg the Matterhorn.
- Ribbon lakes, eg Lake Como.
- Fast-flowing rivers.
- Contrasting microclimates on north facing (ubac) and south facing (adret) slopes.
- Geologically young (30-40 million years old).
Human Activity Surrounding Fold Mountains
- Winter sports such as skiing in resorts such as Chamonix.
- Climbing and hiking in the summer months.
- Summer lakeside holidays, eg Lake Garda.
- Agriculture - takes place mainly on south facing slopes and includes cereals, sugar beet, vines and fruits.
- Forestry - coniferous forests for fuel and building.
- Communications - roads and railways follow valleys.
- Hydroelectric power (HEP) - steep slopes and glacial meltwater are ideal for generating HEP. Hydroelectric accounts for 60 per cent of Switzerland's electricity production.
- The ocean trenches are narrow depressions in the sea. These trenches form the deepest points in the ocean and are the lowest points on earth.
- Ocean Trenches are formed at a particular place of plate boundary which is known as the subduction zone.
- It forms when an oceanic plate hits another oceanic plate or an oceanic plate strikes with continental plate.
- Oceanic plates are made of basalt which is a denser rock while continental plates are formed up of granite which is not as dense as the basalt.
- When one plate hits another plate, the denser plate between the two of them sinks in the mantle.
- The place where this plate sinks will create a deep trench on that spot of ocean.
- They are associated with a chain which is known as island arc or the zones that experience frequent earthquakes.
- The trenches can be very long; up to thousands of km and they may be parallel to island arc volcanoes
Tsunami case study - Japan
- A massive 9.0-magnitude earthquake struck Japan, Friday afternoon, on 11 March 2011 @ 0546 GMT
- The quake was centred 130 kilometres to the east of the prefecture’s capital, Sendai.
- A tsunami was sent crashing into the country’s north-eastern coast.
- It was originally reported at a magnitude of 7.9, but later was upgraded to 8.9 and then to a 9.0.
- It lasted 6 minutes.
- That makes it the fifth largest recorded worldwide since 1900, according to the U.S. Geological Service, larger than the 7.9-magnitude Great Kanto Earthquake that devastated Tokyo in 1923 or the 6.8 magnitude quake that hit Kobe in 1995.
- It had 10,000 times more energy than the magnitude 6.3 earthquake in Christchurch, New Zealand, which struck 17 days earlier
Tsunami case study - Japan. Causes
- Japan is located on the east edge of the Eurasian plate.
- The oceanic pacific plate sub-ducts (sinks under) the Eurasian plate.
- This plate margin is 'destructive' - it is not a smooth process, friction is present and the plates stick.
- When the plates stick, tension builds up.
- When this pressure builds up and is released, it causes a rapid shift in the plates and a lot of energy is released, in this case about the same as the annual energy output in the UK.
Tsunami case study - Japan. Effects
- Two nuclear plants on the Pacific coast in Fukushima were automaticallt shut down.
- At Fukushima the subsequent tsunami disabled emergency generators required to cool the reactors
- Radiation releases caused large evacuations, concern over food and water supplies, and treatment of nuclear workers
- 2,000 people confirmed dead, 10,000 more expected to be, 2,000 injured
- 530,000 people dispaced, staying in 2,500 evacuation centres, such as schools and public halls
- 24,000 people still compeltely isolated and cannot be reached
- 1.2 million homes without power
- 1.4 million homes without water
- 4,700 destroyed houses
- 50,000 damaged houses
- 482 roads cut off
- 32 bridges destroyed
Tsunami case study - Japan. Responses
- The governor of Miyagi Prefecture asked for Japanese military forces to be sent in to help.
- In response, 91 countries offered aid, from blankets and food to search dogs and military transport.
- The japanese fovernment is among the best prepared in the world for disasters and has so far only made specific requests for help, such as calling for search and rescue teams.
- A British rescue team has arrived in Japan to join the search for survivors of the earthquake and tsunami.
- New-age innovations, such as Twitter were bringing updates on the situation far earlier than the media.
- Fifty-nine search and rescue experts, four medics and two sniffer dogs flew out on a private charter plane with 11 tonnes of equipment on board.