PHYSICAL - The Restless Earth Flashcards
What is the crust fractured into?
Tectonic Plates
The Mantle
A zone of molten Silicates and other minerals. Molten so it moves, the source of this is the Earths intence inner heat which sets up convection currents.
How thick is the mantle?
2,900km thick
What are the 2 types of crust?
Oceanic and Continental
What are the characteristics of Oceanic crust
- Denser
- Newer
- Thinner
What are the characteristics of Continental crust?
- Older
- Thicker
- Less dense
What are convection currents?
Heat currents in the molten magma that move the crust above very slowly
Why is the inner core solid?
The inner core is solid (despite temperatures of 3700°C_ because of the intense pressure there
Plate Margin
The edges of plates where 2 plates are either moving apart, colliding together or sliding past one another
What drives plate movement?
Convection currents
Why do convection currents determine the direction of plate movement?
Because slabs of crust fload like rafts on top of the mantle. Heat from within the earth causes the molten rock in the mantle to rise and fall in convecton cells.
These cause the plates to move either together, apart or along side eachother.
Name 3 plate boundries and their type
- San Adreas Fault - Conservative↑↑
- Mid-Atlantc Ridge - Constructive ← →
- Andes Mountains - Destructive → ←
Explain a Constructive plate boundry
Two plates move apart
↓
A ‘gap’ apears
↓
Lava escapes, usually as a gentle erruption
↓
Creates a mid-ocean ridge
Eg Mid-Atlantic Ridge (North American plate/Eurasian Plate)
Explain what happens at a Destructive plate boundry
An ocean crust moves towards a continental crust
↓Denser Oceanic crust is forced down or ‘subducted’
↓
Friction between the plates can cause earthquakes
↓
Friction also causes heat, which melts the ocean plate
↓
Hot magma rises to the surface in violent erruptions
Eg Andes (Nazca Plate and South America plate)
Explain what happens at a Constructive plate boundry
Two plates move apart
↓
A ‘gap’ apears
↓
Lava escapes, usually as a gentle eruption
↓
Creates a mid-ocean ridge
Eg **Mid-Atlanic Ridge **(North American Plate/Eurasian Plate)
Explain what happens at a Conservative plate boundry
Two continental plates move together
↓
They are equally dense, so neither can sink
↓
Sedimentary rocks between the plates are pushed up
↓
Earthquakes occur and fold mountains are formed
Eg **Himilayas **(Indo-Austrailian Plate/Eurasian Plate)
Explain what happens at a Collision plate boundry
Two plates try to move side by side
↓
Friction makes them stick, so movement is very difficult
↓
Pressure builds up steadily
↓
The pressure gets great, so a catastophic slip occurs
Eg **San Andreas Fault **(Pacific plate/North American Plate)
What is the earth divided into (plates?)
- 38 minor plates
- 14 major plates
- 52 segments in total
What are Fold Mountains?
Fold mountains are large mountain ranges where the layers of rock within them ave been crimled as they have been forced together.
How are fold mountains formed?
- Sediments accumulate in shallow seas or epressions known as geosynclines as rivers enter those areas
- This creates a sea or lake bed of layered sedimentary tocks as compression takes place
- Two plates move together because of convetion currents in the mantle
- This starts to crumple the rocks together
- Therocks start to form fold which have anticlines and synclines, which are pushed upwards to form fold mountains
- These mountains are then subject to erosion, weathering and mass movement
Anticlines (fold mountains)
The upward folds of sediment
Synclines (fold mountains)
Downward folds of sediment
Overfolds
When the fold are pushed over to one side forming an overhang
Human settlement in fold mountain areas?
- Valley floor - soils are fertile, deeper and more silty
- High population densitie are found in high regions of Colombia, Ecuador and Peru - rich, fertile, volcanic soils
- The highest settlements found in the Andes where rich mineral resources are present - Copper, Tin, Silver and Gold. They are well above the height of civilisation and owe existence entire to minerals.
Physical Problems of living in fold mountain areas
- Relief - high, steep, rocky outcrops, narrow valleys, little flat land for farming and setlements
- Climate - altitude increases the climate gets wetter and colder, percipitation falls as snow, short growing season and cultivation impossible at high levels
- Soils - stony, thin and infertile
- Accessability - infastructure exoensive to install, travel frequenty disrupted by avalanches and rock falls, high inland areas are accessible only by foot
Name the 4 landforms found at plate boundries
- Fold mountains
- Mid-ocean ridges
- Ocean tenches
- Types of volcano
What is an ocean trench?
Ocean trenches are deep water areas that run along a costline which had a destructive plate margin created by subduction, and mark the point where oceanic crust is being pushed under continental crust.
There is often quite a large section fo continental crust between this margin and the oceans edge, and sometimes a volcanic island arc, such as Japan and the Aleutian islands which can be found in between the trench and the continental shelf
What are mid-ocean ridges?
**Long ridges of mountains created by 2 plates moving apart at a contructive plate margin. **
Where these mountains rise above sea level islands like Iceland are formed.
What is a volcano?
Anywhere on te earths crust where magma escapes from the surface, over time magma is ejected and builds up to form a mountain
Where are Volcanoes found?
Plate boundries and hotspots
What is an active volcano?
A volcano that is constantly erupting
The eruption is usually quit but can sometimes be violent.
Stromboli, an island near Italy, is an active volcano
What is an intermittent volcano?
A volcano that erupts at fairly regular time periods
Eg Mount Asma, Mount Etna, and Haulalai
What is a dormant volcano?
Volcanoes that have not erupted for an amount of time but can’t be called extinct
They create a false sense of security and can be called ‘sleeping’ volcanoes
What is an inactive volcano?
A volcano that has not erupted since the beggining of recorded history
They will never erupt again unless they are still dormant and have been mistaken for extinct volcanoes.
Explain a shield volcano
A place where volcanoes extrude huge quantities of balsatic lava that gradually build a wide mountain with a shield-like profile.
Their lava flows are generally very hot and very fluid
Eg Manua Loa, which rises over 9,000km from the ocean floow and is 120km in diameter and forms part of the largest island of Hawaii
Explain composite(/Strata) volcanos
**Tall cone shaped mountains composed of lava flows and other ejecta in alternate layers, the strata that give rise to the name. **
Eg mount Fiju, Vesuvius and Stromboli
Explain the formation of a volcano
- Molten rock origionates in the mantle, which in turn is powered by the Earths inner heat
↓
- Driven by bouayancy and gas pressure molten rock, which is lighter than the surrounding solid rock, forces its way upward into magma chambers within the eraths surface rocks
↓
- This material accumulates and can exert pressure on the surface, forcing it to buldge upwards
↓
- Some of this material is then forced under pressure to rse towards the earths surface through fissures and cracks, where it will be bloecked by solid rock
↓
- Ultimately, the pressure gets so great that this magma breaks through zones of weaknesses in the Earths crust. This is when an erruption beginds
↓EITHER↓
- High gas pressure, sticky lava (composite volcanoes) 6. low gas pressure (shield volcanoes)
Name the primary impacts of a volcano eruption
- Ash clouds into atmosphere
- Lava bombs and clouds
- Pyroclastic flows
- Lahar - super heated mud flow
Name the secondary impacts of a volcanic erruption
- Ash clouds bloack out the sun
- Fatalities/injuries
- Land gets covered in ash - food production decreases (increases chance of famine)
- Refugess are forced to move due to the disaster
- Volcanic winters
- Loose source of employment eg tourism, farming
Characteristics of a shield volcano?
- Cone with wide base and gentle slopes
- Made of lava only
- Frequent eruptions
- Lava pours out with little violence
Characteristics of a composite cone volcano?
- Tall cone with narrow and steep sides
- Made of alternate layers of lava and ash
- Irregular wit long dormant periods
- Violent explosions possible
Formation of a shield volcano?
As the plates move apart, magma rises upwards from the mantle to fill the gap. This adds new rock to spreading plates. Some of the magma may also be forces out to the surface through a vent. Some volcanoes grow high enough to form volcanic islands.
Explain the formation of a composite cone volcano
When the plates collide, the senser oceanic plate is pushed down into the mantle. Here the plate melts and is destroyed in the subduction zone the plate forms a pod of magma. The great heat and pressure may force the magma along a crack where it erupts at the surface to build a volcano.
What are the advantages of volcanic activity?
- Rich fertile soil - rock full of minerals, making volcanic regios very destructive eg Vineyard slopes of vesuvius
- Geothermal energy is cheap, clean, doeadnt amit greenhouse gases and is very efficient
- Tourism - educational groups - give people jobs and money
- Extracts silca pumica
Disadvantages of volcanic eruption?
- Constant threat of erruption
- Living with frequent erruptions
- People might not visit meaning lack of investment in that area
How much material does a supervolcano emit?
1000 km3
What do supervolcanoes look like
They are hard to spot, but they can look like a large depression called a Caldera and are often marked by a rim of higher land around the edges
Explain a Caldera formation
- Full magma chamber under pressure causes eruption
- Magma chamber now partially emptied, pressure released
- Volcano collapses into top of magma chamber
- Large (60km) crater forms with steep rim
Give 4 characteristics of a supervolcano
- Emit atleast 1,000km3 of materials
- They don’t look like traditional volcanoes, as they are large depression called a Caldera, often a rim of higher ground around the edges
- They have global impacts
- They don’t errupt often
Compare the size of erruptions of; A supervolcano, composite cone and shield volcano
- Supervolcano: Causes a huge depression called a Caldera, causes massive erruptions
- Cone: Large erruptions, depending on the size of the volcano
- Shield: Small, gentle erruptions which don’t cause much damage
Compare the shapes of; A supervolcano, composite cone and shield volcano
- Supervolcano: Doesn’t have cone shape like other volcanoes, its barely visable
- Cone: Large cone like shape, very steep cliffs
- Shield: Slopes caused by runny lava flow
Compare the Impact of: A Supervolcano, composite cone and shield volcano?
- Supervolcano: Massive erruptions that cause global consequences
- Cone: eg death, destruction (housing, farmland) countries, economy
- Shield: Doesn’t have many destructive impacts
What is the focus of an earthquake?
The point inside the crust where the pressure is released
What is the epicentre of an earthquake?
Directly above the focus on the ground
What are seismic waves?
Waves of energy that travel from the focus through the earths layers
Whats a seisometer?
An instrument which measures how strong the seismic waves are. It plots data on a seismograph
Explain the distribution of earthquakes
Earthquakes are in linear clusters eg around the edge of the pacific plate, many on plate boundries (especially on destructive 90%) and also on collision, often where volcanoes are too
What is the richter scale?
It measures the magnitude/strength of earthquakes
How are the shock waves classified on the richter scale?
On a scale of 0 to 9
What type of scale is the richter scale?
A logorhythmic scale meaning each increase is a tenfold increase
When answering a question on the richter scale, how should you explain the tenfold scale?
By giving an example, eg 8 is 10 times bigger than 7, and 100 times bigger than 6
What does the Mercalli scale meausre?
The intensity of the earthquake
How does the Mercalli scale classify earthquakes?
It classifies the effects of the earthquake using Roman numerals from 0 - X11
It takes into account effects on the earths surface, poeple and buildings
How are the numbers on the scale obtained?
By observing the impacts and making judgements, this means it subjective
Preperation for volcanic erruptions?
- Emergency drills
- Warnings
Prevention for volcanoes?
- Evacuation
- Sending out warnings over radios (most people have them, and they can be battery powered)
- Education (eg drills)
- Set up exclusion zones
- Restrict development in danger areas (controversial - controlling people)
Prediction for volcanoes?
- Monitor seismic waves
- Use historical data
- Amount of gases being released
- Test acidity of the water
- Monitor the height and shape of volcano (using satellite data)
- Tiltometers
Preperation for Earthquakes?
- Survival kits (water, first aid, medicine, radios, blankets, shelters)
- Drills and lessons
- Train emergency services
Prevention for earthquakes?
- Earthquake proof buildings (shock absorbers, flexible structures, deep piling)
- Saftey glass on the side of buildings (stops shattering)
- Fixed fittings
- Automtic gas turn off
Prediction for earthquakes?
Much harder to predict
- Monitor foreshocks (smaller seismic shocks)
- Historical data (montor stresses)
- Monitor animal behaviour eg underground animals
*
Preparation for Tsunamis?
Educate people (what to do, where to go)
Prevention for Tsunamis?
- Building things higher up
- Raise sea walls
- Evacuation routes and warning sirens
Prediction for Tsunamis?
- Model them to workout path
- Pressure sensors on the ocean floor
- Buoys detect in sea levels and send it to warning centers
What can Tsunami’s be caused by?
- Landsliides
- Underwater volcanoes
- Earthquakes
