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Geography > Earthquakes and volcanoes > Flashcards

Earthquakes and volcanoes Flashcards

1
Q

Shield Volcanoes

A
  • Have very runny lava (non-viscous) –> thus they don’t have an ‘explosive’ eruption.
  • Lava spreads quickly bc non-viscuous
  • Every eruption = new lava flow = new rock layer on volcano
  • Gradually, wide dome of rock is built up.
  • Has very gentle slopes
  • The Hawaiian islands are a chain of shield volcanoes
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2
Q

Composite volcanoes

A
  • Also called strato volcanoes
  • Most common type of volcano
  • Viscuous lava –> thicker + cools/hardens faster
  • Has steep sides –> cone shape bc of viscuous lava.
  • Formed by hardened layers of lava and ash from past eruptions.
  • Eruptions tend to be violent –> (can produce pyroclastic flows)
  • Mount Vesuvius in Italy is an example of a Composite Volcano.
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3
Q

Active volcano

A

Recent eruptions

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4
Q

Dormant volcano

A

Resting (unrecent eruption)

Volcano that hasn’t recently erupted but still has the ability to.

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5
Q

Extinct (volcano)

A

Won’t erupt again

(could be bc the plates moved and the volcano is off the hotspot which gave it magma to erupt.)

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6
Q

Earthquake

A

Shaking + vibration of ground caused by movements in the Earth’s crust.

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7
Q

Magnitude (of an earthquake)

A

Strenth of an earthquake. Measured using the Richter, Mercalli or Moment scale.

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8
Q

Focus

A

Point underground where shock waves travel out from.

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9
Q

Epicentre

A

Point (on the crust) above the focus with greatest vibrations.

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10
Q

Fault

A

Weak point in tectonic plate where pressure within the crust is released.

A fault is a fracture or zone of fractures between two blocks of rock.

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11
Q

Ways to predict Earthquakes.

A

Earthquakes are notoriously hard to predict (unlike volcanoes).

  • Historical records can be used to assess the level of frequency of large earthquakes
  • GPS technology can monitor the stress build up on faults
  • Monitoring increase in Radon Gas levels escaping from crust.
  • Checking water levels in wells, which may fall before an earthquake as the water seeps into small tension cracks
  • Using seismographs to detect small fore shocks
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12
Q

How to prevent casualties during an earthquake.

A
  • Using earthquake safe building designs. (eg. using strong + flexible material, using base-isolation, using counterweights, using steel-buckling braces)
  • Plan for rescue, restoring essential services and arranging for temporary evacuations.
  • Evacuation routes must be practiced, + individuals need to have mergency kits (food, water, torches etc.)
  • Doing emergency drills (usually in schools) –> drop, cover and hold on. Los Angeles, Tokyo & Mexico City have practised city wide drills.
  • Warning apps / systems due to seismometers.
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13
Q

Crust

A
  • A thin layer of solid rocks around the outside of the earth.

2 types of crust:
* Continental crust is crust made up of land is mainly composed of Granite.
* Oceanic crust is crust made up of oceans it is composed of Basalt.
* The earth’s crust is broken up into large slabs of rock called tectonic plates

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14
Q

Mantle

A
  • A layer of semi-molten (melted rock)
  • The thickest layer.
  • Heat currents called convection currents rise and fall in the mantle.
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15
Q

Outer Core

A
  • A layer of molten (melted) rock.
  • Average temperatures of 3000 degrees C.
  • Composed of iron / nickel.
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16
Q

Inner Core

A
  • The centre of the earth
  • Temperature of about 5000 degrees C
  • Described as a solid ball of iron and nickel
  • It is in a solid state due to pressure from the other layers.
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17
Q

7 Major Tectonic Plates

A
  • The Pacific
  • The Eurasian.
  • The African
  • The American
  • The Indo Australian
  • The Nazca Plate
  • The Antarctic plate.
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18
Q

Tectonic Plates

A
  • Tectonic plates are sections of very thin crust.
  • They float like rafts on the (semi-molten) mantle.
  • These plates move on top of the mantle by a series of heat (convection) currents.
  • Earthquakes and volcanoes are found near plate boundaries (often caused by plate movements).
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19
Q

Convection Currents (Step by Step)

A
  1. Convection currents = heat currents inside the mantle.
  2. Semi-molten rock near the outer core is heated.
  3. As the amgma warms it expands + becomes less dense.
  4. Less dense magma rises towards the crust.
  5. As it nears the crust it begins to cool.
  6. Cooling magma becomes denser + sinks.
  7. Rising + falling magma = circular currents in mantle.
  8. These currents create friction with the crust above –> make the plates move.
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20
Q

Volcanic Bombs

A

Pieces of rock flung out of a volcano during an eruption.

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21
Q

Pyroclastic flow

A

Column of hot volcanic amterial (ash + rock) running down the sides of a volcano

22
Q

Ash cloud

A

Cloud of hot volcanic amterial that has exploded into the atmosphere.

23
Q

Lahar

A

When volcanic ash + mud mixes with water it forms a mudflow called a lahar.

24
Q

Fumaroles

A

A hole (vent) in a volcanic area from which hot smoke + gases escape.

25
Q

Tephra

A

Small pieces of rock and ash.

26
Q

Magma chamber

A

Large resevoir in the crust of the earth that is occupied by a body of magma.

27
Q

Conduit

A

Main artery through which magma flows inside a volcano.

28
Q

Lava dome

A

A build-up of lava on the side of a volcano that may erupt to form a second crater.

29
Q

Crater

A

Large opening in a volcanic mountain created by an intense volcanic explosion.

30
Q

Vent

A

Opening in the earth’s crust through which lava escapes

31
Q

Lava flow

A

Stream of molten rock that is released from a volcano.

32
Q

Destructive / Convergent boundaries

A
  1. Denser heavier oceanic plate subducts under the lighter less dense continental crust.
  2. Friction form the contact between the 2 plates cause very large earthquakes.
  3. As the crust sinks further into the mantle it melts producing magma.
  4. Water + plankton are aso dragged down to the mantle –> they turn into CO².
  5. The CO² along with the magma cause a volcanic eruption bc of pressure.
33
Q

Collision boundary

A
  1. Two continental plates converge (move towards each other.)
  2. Since two plates of land are of a similar density neither is subducted.
  3. Instead, plates are buckled and pushed up to form Fold Mountains (e.g., Himalayas or Alps)
  4. Earthquakes can occur here.
34
Q

Constructive / Divergent boundaries

A
  1. 2 Plates move apart (diverge) due to convection currents.
  2. The sea floor spreads, and magma wells up to fill the gap.
  3. The magma erupts forming a volcano.
  4. New crust is created by the rising magma. (creates mid–ocean ridges = chains of submarine mountains and volcanoes) (eg. Mid-Atlantic Ridge)
  • New crust is continually being made so after a long period of time volcanic islands can be formed. e.g., Iceland.
  • Minor earthquakes occur as the plates pull apart.
35
Q

Conservative/transform boundaries

A
  1. Convection currents cause two plates slide past one another. (opposite direction or same direction, different speed)
  2. Plates can become locked together, pressure builds up as the plates are trying to move and earthquakes occur when the tension is released. E.G. Turkey-Syria Earthquake 2023.
  3. No crust is created or destroyed, and no volcanic
    eruptions take place.
36
Q

Volcanic Hotspot

A
  • Hotspot volcanoes can be found both along and away from plate boundaries.
  • Hotspots are unusually hot magma plumes that rise in the mantle erupt through the crust.
  • This creates seamounts which are volcanic mountains beneath the sea.
  • Seamounts can rise above the ocean surface to create islands.
  • The Hawaiian Island chain formed as the Pacific crustal plate moved over a stationary source of magma or hotspot.
  • There are many volcanoes on the Hawaiian islands, however, only a few are active.
  • When volcanoes move off the hotspot they lose their source of magma and become extinct.
37
Q

Eyjafjallajökull - Basic Information

A

Location - Glacier volcano lays within the country’s East Volcanic Zone,

Date of eruption - April 2010

38
Q

Eyjafjallajökull - Causes

A
  • Iceland formed at a divergent plate boundary (north american + eurasian plate moving apart, 1-5 cm annually) + Iceland lies over a hotspot.
  • Plate boundary creates Mid Atlantic Ridge + Iceland + chain of volcanoes along the SE Rift zone of Iceland.
39
Q

Eyjafjallajökull - Effects

A
  • 800 people evacuated due to glacial outburst floods.
  • Travel disrupted –> 95,000 flights cancelled between 14-21 April 2010.
  • Eruption produced 0.3 cubic kilometres of ash.
  • Economic losses of 5 billion euros.
  • Businesses lost trade.
  • Perishable foods were wasted as they could not be transported.
  • People were stranded –> unable to get to work.
  • Timing of the disruption was during Easter holidays –> levels of tourism were high.
40
Q

Eyjafjallajökull - Prediction

A
  • Gas sampling: changes in gas composition indicate the activity levels of magma underground.
  • GPS technology: used to monitor any significant changes on the volcano so that the risk of activity e.g. pyroclastic flows can be assessed.
  • Seismic monitoring: any minor earthquake activity is detected using seismographs and is recorded. Rising blobs of magma can cause earthquake activity and so this may be a sign of an eruption.
41
Q

Eyjafjallajökull - Prevention

A
  • Glacial outburst floods : Caused when heat from the volcano melts glacial ice, are a real risk in Iceland. 800 people were evacuated when the volcano flooded as they were in a flood risk zone.
  • Aircraft were prevented from flying into/out of northern Europe for 6 days as there were concerns that the ash cloud could cause safety risks.
42
Q

Why people live in Iceland despite the risk?

A
  • Volcanic activity is closely monitored using seismometers + GPS technology.
  • Tourism jobs in Iceland - There is a Lava Interactive Centre (museum about Iceland)
  • Geothermal energy - 66% of electricity geothermal
  • Ash from volcanic eruptions cause fertile soil –> agriculture.
43
Q

Methods for earthquake prediction

A
  • Historical records can be used to assess the level of frequency of large earthquakes e.g. southern California experiences a large earthquake once every 150 years on average.
  • Using GPS technology to monitor the stress build up on faults.
  • Monitoring an increase in the escape of radon gas, which may suggest the approach of an earthquake.
  • Checking water levels in wells, which may fall before an earthquake as the water seeps into small tension cracks.
  • Using seismographs to detect small fore shocks.
  • Strange animal behaviour.
  • Anomalies in Earth’s magnetic field.
44
Q

Methods for earthquake prevention

A
  • Construct buildings and infrastructure (bridges, roads etc.) that can withstand the earth shaking. Techniques include using strong materials e.g., concrete and flexible materials e.g., steel. Use of base isolation (explain its use), use of counterweights (explain their use).
  • Plan for rescue, restoring essential services and arranging for temporary evacuations.
  • Evacuation routes must be practiced, and individuals need to have emergency kits with things like food, water, torches etc.
  • Doing emergency drills e.g., in schools. Earthquake prone cities have also practiced city wide earthquake drills e.g., in cities such as Los Angeles, Tokyo & Mexico City.
45
Q

Turkey Earthquake - Causes

A
  • Transform/conservative plate boundary - Anatolian plate is sliding past the Arabian plate.
  • Tension had been building up for a long time on the East Anatolian fault.
  • Pressure was released and the plates slipped along a strike slip fault.
  • Shockwaves were sent out causing severe shaking of the crust.
  • The earthquake measured 7.8Mv.
  • As is the case with many earthquake events the mainshock was followed by many aftershocks, including three above magnitude 6.0.
  • Aftershocks represent minor re-adjustments along
    the portion of the fault that slipped at the time of the mainshock.
46
Q

Turkey Earthquake - Impacts

A
  • 55,000+ deaths across SE Turkey and NW Syria.
  • 6500 buildings in Turkey collapsed across 10 cities, including a 2000 year old castle in the city of Gaziantep.
  • Hundreds of thousands left homeless across SE Turkey and NW Syria.
  • People left to fend for themselves with many camped out in makeshift shelters in supermarket car parks, mosques, roadsides or amid the ruins, often desperate for food, water and heat.
47
Q

Why was the Turkey earthquake so bad?

A
  • It was a major earthquake (7.8) with strong aftershocks (7.5).
  • Earthquake struck close to large urban settlements + densely populated areas with many Syrian refugees.
  • Cold winter weather made relief efforts difficult + people trapped under rubble have less chance of survival.
  • No earthquakes above magnitude (7.0) since 1800 –> badly prepared.
  • Turkey has seismic building codes but many buildings pre-date the codes and buildings had not been retrofitted.
  • In some cases, it also seemed that proper building codes had not been followed due to corruption - this was seen in the many new apartment buildings that collapsed.
  • Despite residents paying an earthquake tax for years, the emergency response to the earthquake was found to be poor - people complained of a lack of equipment, expertise and support to rescue those trapped under rubble.
  • Relief to Syria was complicated by the ongoing civil war in the country.
48
Q

Turkey Earthquake - Management

A

Prediction

  • Seismologists use GPS technology to analyse stress build-up on faults. The East Anatolian fault was predicted to have a large earthquake soon.

Prevention

  • Turkey introduced a seismic building code after a large earthquake in 1999. However, many buildings pre-date the codes and some recent buildings have also not been built to code due to corruption (developers paid money to officials and got a certificate saying the building was safe)
  • People in SE Turkey paid an earthquake tax - this is meant to help with relief efforts; however, the efforts were found to be poor with people complaining of a lack of equipment, expertise and support to rescue those trapped under rubble.
  • Countries, such as the USA, deployed search and rescue personnel to Turkey (the US sent 150 specialists).
  • UN aid convoys were not permitted access to Syria to provide assistance until 3 days after the earthquake.
  • The international community pledged aid to Turkey and Syria.
  • Mexico sent search dogs to help.
49
Q

Why people live in California

A
  • San Andreas fault = transform fault
  • Early warning systems alert people ($1 billion annually backed)
  • Schools often practise emergency drills
  • Buildings have earthquake proof designs (eg. One Rincon Hill built with steel buckling-restrained braces)
  • Silicon Valley = many jobs (700,000 people employed)
  • California = good healthcare + educaiton = good standard of living
  • Beautiful coast + nice climate, (summer = 30C, winter = 10C + low rainfall)
50
Q

How to predict volcanoes

A
  • Lasers to detect physical swelling of the volcano.
  • Chemical sensors to measure the increases in sulphur levels.
  • Seismometers detect large numbers of earthquakes caused by rising magma.
  • Sattelite imaging shows ground surface temp due to rising magma
51
Q

How to manage volcanoes

A
  • Having an evacuation plan eg. supplies of food / water, medical facilities etc.
  • Ready to establish exclusion zones if needed.
  • Gov agencies such as police organise evacuations
  • Ability to redirect lava flow (water jets)
  • Ability to redirect flooding (widening rivers artificially.)

Geography (14 decks)

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