The Restless Earth Flashcards
What is continental drift?
The theory that describes how plates have moved over millions of years.
What is plate tectonics?
The theory that describes the movements of the Earth’s surface (crust). It explains the distribution of fold mountains, earthquakes and volcanoes, and the process of continental drift.
What are the layers of the earth?
The inner core, the outer core, the mantle and the crust on the surface.
What cause the plates on the surface to move?
The sideways movement of rocks just beneath the crust.
What are the properties of oceanic crust? (in comparison to continental)
Newer - most less than 200million years old
Denser
Can sink
Can be renewed and destroyed
What are the properties of continental crust? (in comparison to oceanic)
Older, most more that 1500 million years old
Less dense
Cannot sink
Cannot be renewed or destroyed
Describe the process of convection current in the mantle
- Radioactive decay in the core heats the molten rock (magma)
- The heated magma rises as it becomes less dense.
- The magma moves away from the heat source and spreads out.
- The magma cools and starts to sink.
- The cycle of the convection cell restarts.
Describe what happens at a constructive plate boundary
- The plates are moving apart due to convection currents inside the earth.
- As the plates move apart, cracks and fractures form between the plates where there is no solid crust.
- Magma rises from the mantle and erupts at the surface of the earth in a volcano. Earthquakes also occur.
- The magma cools and solidifies to form a new crust of igneous rock. This process is repeated over millions of years.
What land forms are created at constructive place boundaries?
Rift valleys e.g. East African Rift Valley
Ocean ridge e.g. Mid Atlantic ridge (a series of underwater volcanoes)
Describe what happens at a conservative plate boundary
- At a conservative plate boundary, the plates are sliding past each other. They are moving in similar directions at slightly different angles and speeds. Because of this, they tend to get stuck.
- Eventually, the build up of pressure causes pressure to be released. This sudden release of pressure causes earthquakes.
What landforms are created at conservative plate boundaries?
Upland Ridge e.g. San Andreas fault - land is buckled and folded but on a smaller scale due to tension between the plates as they move past each other.
Describe what happens at destructive (subduction) plate boundaries
- Convection currents in the mantle cause the plates to move closer together.
- The oceanic plate is denser so, as they move together, the oceanic plate is forced underneath the continental plate. The point at which this occurs is the subduction zone.
- The oceanic plate melts to form magma and earthquakes are triggered due to friction.
- The magma collects to form a magma chamber and rises up through the cracks in the continental crust. As pressure builds up, a volcanic eruption can occur.
What are landforms created by destructive subduction?
Ocean trenches e.g. Mariana Trench.
What is an ocean trench?
A long, narrow depression of the sea floor caused by subduction at a destructive boundary.
Describe what happens at destructive collision boundaries
- If the two continental plates meet each other, they collide rather than one sinking beneath the other.
- The rocks buckle and fold upwards to form fold mountains
- Plates are the same density so little or no subduction takes place. Earthquakes also occur.
What are landforms created by destructive collision?
Fold mountains
What are fold mountains?
Highland areas formed along plate boundaries where great compressive earth movements take place at collision boundaries.
How are fold mountains formed?
Over millions of years from sedimentary rocks which have been forced upwards into a series of folds by the movement of tectonic plates.
Describe the process of the formation of fold mountains
- Rivers carry and deposit sediment into huge depressions in the sea called geosynclines.
- There are long periods of quiet between earth movement during which sediments, thousands of metres thick, build in these geosynclines.
- These sediments are then forced upwards into a series of folds by the compressive movement of tectonic plates.
- These sediments can be upfolds (anticlines) or downfolds (synclines). These rocks can also be fractured or faulted.
What are geosynclines?
Large scale depressions in the earths crust containing a thick series of sediments.
How do people use the Alps for farming?
On sunny south facing slopes - vineyards.
Dairy farming i.e. transhumance system (seasonal moment of animals) - summer: cattle taken high up to graze, crops grown on the valley floor because of the warm and fertile soil, winter: animals kept in sheds on the valley floor and fed summer crops.
How do people use the Alps for mining?
Salt, iron all, gold, silver and copper were all mined but has dramatically decreased due to foreign sources.
How are the Alps used for hydroelectric power
The steep slopes, high precipitations and summer melting of the glaciers produce fast flowing rivers.
The narrow valleys are easy to dam and there are lakes to store water.
The cheap hydroelectric power is used by industries which require high input of electricity e.g. sawmills and electrochemicals.
Some electricity is exported to other regions to supply towns and cities Switzerland get 60% of its electricity from hydroelectric power stations in the Alps.
How are the Alps used for tourism?
Hundred million tourists visit the Alps each year.
Summer attractions include glacial lakes, scenery, walking, biking
Winter attractions include skiing, snowboarding, steep slopes, flat land on high Alps is easy to build on
New villages have been built
How have local people adapted to the conditions in the Alps?
Steep relief - goats are farmed because they have adapted to steep mountains, trees and man made defences use to protect against avalanches and rockslides
Poor soils - animals are grazed in most high areas as the soil isn’t great for growing crops
Limited communications:
Roads are built over passes (lower points between mountains) E.g. Brenner pass between Austria and Italy
Tunnels have been cut through mountains e.g. Mont blanc tunnel as it takes a long time to drive over passes and they can be blocked by snow
Electrified railways link the Alpine Valleys to cities e.g. Brenner and Saint Bernard.
Mountain cog railways, cable cars and chairlifts for skiers.
What is an earthquake?
A sudden release of energy or pressure from the earth’s crust that produces seismic shockwaves.
What is the focus of an earthquake?
The point where an earthquake originates - the shallower the focus, the more damaging and felt the earthquake is.
What is the epicentre of an earthquake?
The point of the Earth’s surface directly above the focus of an earthquake.
What is the Richter scale?
Measures the magnitude of an earthquake
No upper limit
Logarithmic scale
Quantitive measure
What is the Mercalli scale?
Measures the destructive power of an earthquake
1 to 12
Qualitative measure
What are the causes of earthquakes at a destructive (subduction) boundaries?
Subduction exerts pressure on the crust Pressure from seduction and melting
Broadbelt of earthquakes, depth increasing with distance from margin
Strong, high magnitude earthquakes
Causes of earthquakes at conservative boundaries
Pressure and tension builds up due to friction as the plates move past each other and get stuck
New zone of usually shallow depth earthquakes
Moderate to high magnitude of quakes, infrequent.
Causes of earthquakes at constructive boundaries
Tension from the gentle extension of the plates and margin
Earthquakes quite close to the centre and narrowly concentrated
High frequency but low magnitude earthquakes
What are primary effects of earthquakes?
The immediate effects that happen after the earthquake, these are most severe when there is a high population density in a developed area. e.g. building collapse, road damage, injuries/deaths.
What are the secondary effects of earthquakes?
The after effects such as fires, tsunamis, landslides and disease.
Factors affecting the effect of an earthquake:
Magnitude of the earthquake
Depth of the focus
Proximity of the epicentre
Geology
Land use
Time of the day
Housing/Building quality
Warning procedures
Education
Wealth of the country
How does geology affect the effect of earthquakes?
Weaker or more porous rock is more susceptible to liquefaction.
What caused the Christchurch earthquake?
New Zealand is located in the pacific ring of fire.
Strike slip movement east and west and upwards movement on a previously unknown fault line in south east Christchurch
Christchurch earthquake basic info and location
5km depth, magnitude 9.3, 22nd February 2011, 12:51pm
Christchurch is located on the southern island of New Zealnd
What is GeoNet?
A national network of instruments and data centres.
This detects and monitors earthquakes and provides info to emergency services almost immediately after an earthquake.
Protection strategies in the Christchurch earthquake:
Part of the AMI stadium was reinforced by a vast network of 10m stone columns covering an area of 1200m2 - but this was not enough to protect subsidance of the stands by approx. 40cm. They are now considering driving piles down 25m to reach solid ground.
NZ has a building code for earthquakes - resistant buildings since 1935. Older buildings have not been reinforced on the South island as it is less earthquake prone, so are more vulnerable.
Preparation strategies in Christchurch
Geonet organises public education about earthquakes and a campaign that encourages people to ‘Quakesafe’ their homes.
GeoNet provides earthquake insurance for home owners as the insurance companies can’t afford to.
Primary impacts of Christchurch earthquake
70% of the buildings in the CBD were demolished
165,000 areas, 222,000 homes were affected (many uninhabitable)
181 people killed
Significant slope failure in upland Port Hills area - rock and debris
Secondary impacts of the Christchurch Earthquake
Big decline in electronic payments because of damage to ATMs
Communities broken apart as people are forced to move elsewhere
13 schools closed, 18 merged, 4500 pupils lost due to out migration
15% fewer exports went through Christchurch airport in October 2012 compared to the previous year.
Immediate responses of Christchurch EQ?
CBD of Christchurch was evacuated
Becuase of the ATMs, additional cash was vital - NZ $150mn cash was sent to christchurch on the week following the EQ.
The government established the Canterbury Earthwuake Recovery Authority to start the reconstruction of the city.
Longterm responses of Christchurch EQ?
The Christchurch Central Recovery Plan set out the way in which the central area of the city would be redeveloped.
Nearyl NZ$1 billion of planning consents were granted in the first 6 months of 2012, to help people rebuild their homes and livelihoods.
The government intends to spend NZ$1m in the next 10 years renewing the education system in the affected areas.
Causes of the Haiti Earthquake?
A conservative fault runs through Haiti between the Carribean plate and the North American plate. It was caused by the release of pressure between the two plate. The Carribean plate was moving eastward from the North American plate.
It caused a strike-slip fault - where two sections fo Earth’s crust are grinding past each other in opposite directions.
Earthquake info Haiti EQ and location
Magnitude 7, 9.97km depth, 4:53pm, 10km southwest from the capitcal Port-au-Prince
GDP$1300
Haiti is located in Central America in the Caribbean
Primary impacts of Haiti EQ
105,000 houses destroyed, over 188,383 badly destroyed
Roads and docks in Port-au-Prince destroyed, difficult to deliver food, clean water, clothes and medicine
19 million m2 of rubble and debris in Port-au-Prince
Over 220,000 deaths
Secondary impacts of Haiti EQ
Disease due to no clean drinking water and rotting dead bodies - cholera outbreak, 5899 killed, 216,000 infected.
4000 schools damaged or destroyed
1.5 million living in homeless camps
People trying to rebuild houses without the availability of money and materials
1 in 5 jobs lost due to the EQ
Immediate responses to the Haiti EQ
Many countries responded to the appeals for aid - money, rescue and medical help - British public declared £107m
Rescue and aid efforts were slowed by the dammage of communication systems, tranport (air, land and sea), hospitals and electrical networks
Further delay - confusion over who was in change, air traffic congestions and problems with prioritization of flights
Morgues overwhelmed in Port-au-Prince 10,000s of bodies having to be buried in mass graves
1.3m put into homeless shelters
Long term responses in the Haiti EQ
1000s of EQ affected families were provided with agricultural asistance including 4,000 tonnes of crop seeds
1 million children recieve daily meals through the National Scould Feeding Programme
The EU gave $330m and the world banc concluded the country’s debt repayments for 5 years
The Senegalese offered land in Senagal to any Haitians
As of June 2011, 1.2 m people had benefited from water provision receiving more than 4,200m3 of water daily
Nearly 500,000 people have been provided with improved temporary shelter
6 months after the EQ, 98% of rubble remained uncleared, some still blocking the access roads.
What is a tsunami?
A special type of wave, where an event, often an earthquake, moves the entire depth of water apart.
Causes of tsunamis (4)
Earthquakes
(Submarine) Landslides
(Submarine) Volcanic eruptions
Meteorite impacts in the ocean
How do tsunamis form?
- Tectonic upthrust (e.g. earthquakes) causes a vast quantity of water to be displaced in a very short space of time generating a huge amount of energy
- In the open sea, tsunamis travel up to 800km per hour and commonly go unnoticed as they pass beneathe ships because they are usually less than 1m high and the distance between wave crests is typically 100s of kilometres.
- As the tsunami approaches the coastline, they are slowed dramatically by friction to around 40 km/h. The wavelength becomes shortened and the wave amplitude increases. One of natures warning signs of a tsunami is the sudden withdrawal of the sea from a coastal region.
- Finally with the wavelength compressed and heightened to 5-10m the wave collides with the shore causing huge damage. Tsunamis consist of a series of waves that surge on shore for as long as 30 minutes. The succeeding outflows continues the destruction causing more damage to people and property. Furthermore, after the first wave hits, more waves follow at 20-60 minute intervals.
Location of Tohoku tsunami
North East Japan, the Tohoku tsunami was caused by an earthquake in the Pacific Ocean
Causes of Tohoku tsunami
Japan is at the centre of 4 plates with destructive subduction and conservative boundaries. Earthwuake occured on the subduction zone between the Pacific Plate and Okhotsk Plate
15-45 minutes after the earthquake struck, it caused tectonic upthrust and a large quantity of water was displaced, causing a tsunami that hit the east of Japan
Japan EQ and Tohoku tsunami information
Magnitude 9.0, 11th March, 2:46pm
Tsunami height” 5 - 20m, max vertical shift almost 40m
Primary impacts of Tohoku tsunami
16,000 known deaths
3000 people missing
130,000 buildings destroyed, twice as many damaged
Rikuzentahaka - 8368 buildings destroyed
Ishonomaki - at Okawa Elementary School 74/108 children and 10/14 teachers died
Estimated 26.7mn tonnes of debris
Secondary impacts of Tohoku tsunami
Water flooded water-cooling systems at Fukushima Daiichi nuclear power plant - systems failed, 3 nuclear units experienced meltdown
- caused immediate evacuation of the area within 20km
Damage caused by harmful pollutants that were emitted
Expected acceleration of ageing, low fertility and outmigration of population
Immediate responses of Tohoku tsunami
Search and rescue and stabilisation and prevention of further nucleur disaster by Japanese government
Operation USA - sent shelter and medical supplies
- first shipment of a $1.1m donation of Gap brand winter clothing was distributed to 10,000s of people in Miyagi, Fujushima and Iwate for the cold winter weather following the disaster.
Long term responses of the Tohoku tsunami
Naoto Kan commissioned a report for the three principles of recovery: safety, sustainability and compassion.
It took 11 months to establish the Reconstruction Agency due to political infighting
The Reconstruction Agency established with these policies:
- focus on local communities and human linkages within Japan
- base survival on ‘self aid’
- develop conditions for mutual and public aid
What is a volcano?
An opening or vent in the Earth’s surface through which material (magma, gas, ash) erupts. They are a tectonic hazard.
What is a hotspot? What does it cause?
A volcanic hotspot is an area in the mantle from which heat rises as a thermal plume from deep in the Earth.
High heat and lower pressure at the base of the tectonic plate facilitates melting of the rock
This melt, called magma, rises through the cracks and erupts to form volcanoes.
What are the three states of volcanoes?
Active - one that has erupted in the last 10,000 years
Dormant - one that hasn’t erupted in the past 10,000 years but which is expected to erupt again
Extinct - one that nobody expects to ever erupt again
Main features of a volcano and what they are
Crater - created after an eruption where the top is blown off the volcano
Main vent - the main outlet for the magma to escape
Secondary vent - smaller outlets through which the magma escapes
Magma chamber - a collection of magma inside the Earth below the volcano
Features of a composite volcano
Found on destructive (subduction) boundaries
Violent explosivity
Rare
Hazards: pyroclastic flows, lahars
Formation of composite volcanoes
Describe what happens at destructive subduction boundary.
Made up of ash and lava that is erupted, cooled and hardened into layers. The lava is usually thick and flows slowly. It hardens quickly to form a steep sided volcano.
Charcteristics of a shield volcano
Found on constructive boundary
Gentle explosivity - limited pressure
Frequent
Hazards: gases and lava flows
e.g Mauna Loa, Hawaii
Formation of shield volcanoes
At constructive margins the magma rises up into the gap created by the plates moving apart.
The lava is runny, so flows quicly and spreads over a wide area, forming a low, flat volcano.
Characteristics of dome volcanoes
Made of only lava
Lava is thick, it flows slowly and hardens quickly forming a steep sided volcano
What are pyroclastic flows?
Hot volcanic ash and rock and hot expanding gases move at tremendous velocities - up to 300km/h.
What are lahars?
Ash is liquified by rain or snow melt, hot or cold mudflows, 100 km/h
What is volcanic gas?
Harmful gases can be emitted like CO2, SO2, Radon, killing people and other living things
Primary effects of volcanoes?
Destruction of wildlife and vegetation
Deaths and injuries
Damage to infrastructure
Immediate decline in tourism
Secondary effects of volcanoes?
Greenhouse gases contribute to global warming
The ash causes soil to be fertile
Acid rain
Ash cloud can cause global disruption
Can attract tourists
Permanent evacuation due to covering of ash
Disruption to transport
Why do we predict volcanic eruptions?
To minimise damage
Ways that scientists predict volcanic eruptions
Scientists can monitor the tell-tale signs that come before a volcanic eruption - tiny earthquakes, escaping gas from the vent eg SO2, changes in the shape of the volcano (bulges where the magma has built up)
Past frequencuy of eruptions and the gap between them
Tiltmeters can identify small, subtle changes in the landscape
Location of the Eyjafjallajokull volcano
Located in Iceland, an island located immediately south of the Arctic circle
Tectonic setting of Iceland
It sits on the mid atlantic ride, the conservative plate boundary between the Eurasian and North American plates - these plates move apart a few cm a year
This produces volcanic rift zones, where magma rises up, and where it reaches the surface, erupts as lava and ash
Iceland is also located on a hotspot so is seismically active for that reason
Specific causes of the Eyjafjallajokull eruption
Fissure eruption. the eruption occured from linear fissures that run parallel to the volcanic rift zone.
The summit crater punched through the ice cap, causing cold meltwater to mix with magma, cooling it rapidly
This caused the magma to fragment explosively into a large quantity of very fine ash that was ejected into the atmosphere
Negative primary impacts of the Eyjafjallajokull eruption
150m thick ice cap melting, 8000 people evacuated from flooding
20 farms destroyed by flooding and ash
Ash blocked out - sun turned day to night
Local water supplies contaminated with fluoride
Ash cloud - 6 flightless days - 17000 flights/day cancelled
Postive primary impacts of the Eyjafjallajokull eruption
Temporary reduction in aircraft noise
2.8m tonnes less of CO2 emitted
No deaths
Secondary negative impacts of the Eyjafjallajokull eruption
Ash silted rivers and caused blockages one year later
Shares in air travel and tourism agencies decreased by 4%
Meltwater produced caused a road to be breached in order to protect a bridge
Closed European airspace - in Kenya, farms depend on air transport to export vegetables and flowers to Europe - unable to be transported, food crops perished, farming operations halted
Secondary positive impacts of the Eyjafjallajokull eruption
Boost to Iceland’s tourism - visitor centre opened near volcano
10% increase for avis in cross-border hire car demand
Immediate responses to Eyjafjallajokull eruption
800 people evacuated from homes and villages (BUT NO DEATHS)
Rescuers wore face masks to prevent them from choking on the dense cloud of ash
Long term responses to the Eyjafjallajokull eruption
EU funded a project called FutureVolc to install sensors to allow for real-time data analysis:
- the monitors can detect minute movements or tremors within the ground and detect any curving of the Earth’s surface around the volcano which could indicate magma build up
- other sensors will look for changes in gas emissions from active sites which could suggest movement of magma up through the Earth’s surface
Easyjet and Airbus are currently testing systems that it says will enable planes to detect and circumnavigate ash clouds
What is a supervolcano?
A mega collosal volcano that erupts at least 1000km3 of material
Where are supervolcanoes located?
Destructive plate margins and hotspots e.g. Yellowstone, USA
How does a supervolcano form?
1) Rising magma cannot escape, and a large bulge appears on the surface
2) The bulge eventually cracks, creating vents for lava to escape through. Lava erupts out of the vents, causing earthquakes and sending gigantic plumes of ash and rock into the air.
3) As the magma basin empties, the bulge is no longer supported, so it collapses (spewing out more lava) - this forms a large depression called a caldera.
Characteristics of supervolcanoes/how they are they different to volcanoes
They are flat with large depressions called calderas, often marked by a rim of higher land around the edges - volcanoes are like mountains, cone-shaped with a crater.
They cover a much larger area - much bigger than volcanoes.
They emit at least 1000km3 of material - volcanoes erupt more like 1km3.
They erupt less frequently, eruptions are 100,000s years apart
Likely effects of a supervolcanic eruption
Local/National: A thick cloud of super heated gas and ash will flow at high speed from the volcano, killing, burning and burying everything it touches. everything within 10s of miles will be detroyed.
The ash will also settle over 100s km2, burying fields and buildings (ash from normal volcanoes usually covers a couple of km2)
Global: Ash will shoot into the air and blockout almost all daylight over whole continents. this could trigger a volcanic winter as less heat energy from the sun gets ot the earth.
Difficult to grow food, crops fail, plants can’t photosynthesise
People emigrating - migration crisis
Material will reach countries thousands of km away within 5 days
What are shock waves?
Vibrations (the earthquake)
Shock waves spread out from a focus, near the focus the waves are stronger and cause more damage
