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Geography > Geophysical Hazards > Flashcards

Geophysical Hazards Flashcards

1
Q

what is the structure of the earth from outside to in

A
  • thin rigid crust, composed of the continental crust and thinner oceanic crust
  • underneath is a flowing but solid mantle that makes up 82% of the volume of the Earth
  • Deeper still is a very dense and very hot core:
    -> outer core is liquid
    -> inner core is solid

These concentric layers become more dense in the centre, and are controlled by temperature and pressure

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2
Q

what is the asthenosphere?

A

the layer underneath the lithosphere

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3
Q

what is the plate tectonics theory

A

the theory that the outer shell is divided into several plates that glide over the mantle, called the continental drift -> first proposed by scientist Alfred Wegener in 1912

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4
Q

where does the earth’s heat come from?

A

The flow of heat from the Earth’s interior to the surface comes from 2 main sources:

  • Radiogenic -> radioactive decay of material in the mantle and the crust
  • Primordial heat -> the heat lost by the Earth as it continues to cool from its original formation
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5
Q

what are the 3 mechanisms related to plate movement?

A
  • subduction
  • plume
  • rifting
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5
Q

how to convection currents operate

A
  1. hot magma rises through the core to the surface
  2. and spreads to the mid-ocean ridges
  3. the cold solidified crust sinks back because it is heavier and denser than the surrounding metal
  4. the cause of the movement is radioactive decay of uranium and potassium in the mantle
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6
Q

what is subduction?

A

subduction refers to the plunging of one plate below another

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7
Q

what is the process of subduction

A
  1. oceanic lithosphere plates collide with another plate - whether is continental or oceanic
  2. The oceanic plate is a lot denser than the continental
  3. the subducting plate is forced to subduct and creates a subduction zone
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8
Q

what is a plume?

A

refers to a small area of unusually high heat flow. Plumes can cause movement (the outward flow of viscous rock from the centre) that may create a drag force on the plated causing them to move. Most occur on a plate boundary, such as the Hawaiian Hotspot

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9
Q

what is rifting?

A

Rifting occurs at constructive plate boundaries, where magma rises and pushes two plates away from each other, for example, the North American and Eurasian plates are moving away from each other.

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10
Q

what is believed to be the main cause of rifting?

A

hotspot activity

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11
Q

where are volcanoes located?

A

most are found usually over plate boundaries, however, there are some exceptions, i.e. volcanoes in Hawaii form over hotspots

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12
Q

where in the world are they distributed?

A

most around the Pacific Ring of fire

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13
Q

what are the 3 different types of volcanoes?

A
  • shield
  • composite
  • cinder
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14
Q

how do shield volcanoes form?
what do they look like?
are they explosive?
example

A
  • formed from very hot runny basaltic lava
  • shield volcanoes are formed with gently sloping slides, shallow crater and a large circumference
  • they build up with no explosive activity or ejected fragments
  • e.g. Hawaii
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15
Q

how do composite volcanoes form?
what do they look like?
are they explosive?
example

A
  • most common -> formed by alternating eruptions of fragmented material followed by lava outflows/pyroclastic flow
  • has slopes of 30º near the summit and 6-10º near the base, and was layers of lava with a crater on top
  • sometimes explosive and erupts after a period of inactivity
  • e.g. Mount Etna, Italy
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16
Q

how do cinder volcanoes form?
what do they look like?
are they explosive?
example

A
  • formed by fragments of solid material which accumulate as a steep conical hill around the vent to form a cone
  • shape depends on the nature of material
  • usually concave as material spreads out near the base and has a steep angle of 30-40º
  • violent eruptions -> lava ejected into broken rocks and fragments into the atmosphere
  • e.g. Big Cinder Butte, USA
17
Q

what are the 2 types of eruptions

A
  • lava eruption
  • pyroclastic eruptions
18
Q

what is a lava eruptions - silica rich + example

A

when the ocean meets the continents, silica-rich sediments are absorbed and cause the lava to become more viscous. It blocks vents until enough pressure has built up to break the open.

I.e. Japan

19
Q

what is a lava eruption - basaltic lava + example

A

Silica content in a lava eruption makes the difference between continuously erupting or those that erupt infrequently but are violent when they erupt

I.e. Hawaiian eruptions are low in silica. Runny basaltic flows down volcano sides and gases escape easily -> Involve a central vent

20
Q

what is pyroclastic eruption - strombolian + example

A
  • explosive eruptions that produce pyroclastic flow
  • commonly marked by a white cloud of steam emitted from the crater
  • frequent gas explosions blast quantities of runny lava into the air, and when these settle and cool they form the cone of the volcano

i.e. stromboli volcano, Italy

21
Q

what is pyroclastic eruptions - Plinian eruption

A
  • extremely violent characterised by huge clouds of pulverised rock and ash that are kilometres thick
  • gas rushes up through sticky lava and blasts ash and fragments into the sky in huge explosions
  • Gas clouds and lava can also rush down the slopes
  • part of the volcano may be blasted away during the eruption
22
Q

what are primary hazards

A

the direct impact of an eruption i.e. lava flows, ash fallout, pyroclastic flows and gas emissions

23
Q

what are secondary hazards

A

may be due to the way the ejected material reacts and changes i.e. ash may join with rainwater to form mudflows and create glacial flooding

24
Q

what are the 2 types of landslides

A
  • debris avalanche
  • lahar
25
Q

what are debris avalanches + example

A

shallow landslides, saturated with water, that travel rapidly downslope as muddy slurries. They occur around the same time as an eruption

i.e. mount st helens, USA

26
Q

what are a lahars

A

they are a combination of heavy rain and unstable ash

27
Q

what are pyroclastic flows? + example

A

this is when ash and debris have travelled through the air and fallen to the ground. This fine ash can damage people’s lungs, it can also damage buildings as it is too heavy

i.e. Unzen Volcano, Japan

28
Q

what is the recurrence interval or return period

A

the expected frequency of occurrence in years of an event of a particular size.
Small events occur more frequently than larger ones

29
Q

which volcanoes erupt more frequently?

A

less explosive eruptions occur more frequently (Hawaiin), larger more explosive volcanoes erupt less often (plinian eruptions)

30
Q

how can we predict volcano eruptions?

A
  • seismicity recording earthquakes and thermal monitoring which occur as magma rises
  • GPS - ground deformation
  • monitor gas emissions
31
Q

how do we measure the size of the volcanic eruptions?

A
  • using the volcanic explosivity index (VEI) to describe and compare the size of volcanic eruptions
  • uses a scale from 0 (non-explosive) to 8 (explosive)
  • log scale -> increases by a factor of 10
32
Q

what factors do the VEI use to measure the magnitude of a volcano?

A
  • the amount and height of volcanic material ejected
  • how long the eruption lasts
  • qualitative descriptive terms
33
Q

what is the richter scale?

A

a logarithmic scale that measures the power of an earthquake. Earthquake of 5 on the Richter scale is 10 times more powerful than an earthquake of 4

34
Q

what is the moment magnitude scale

A

measures the amount of energy released and produces figures similar to the Richter scale. For every increase of 1 of the M scale, the amount of energy released increases by over 30

35
Q

what are the factors that the Moment magnitude scale measures

A
  • resistance of rocks
  • size of seismic waves
  • area of the fault surface broken by the earthquake
  • amount of slippage/rock movement
36
Q

what is a hazard risk

A

when people or property are at risk

37
Q

what causes places to be at risk from geophysical hazards

A

behavioural school of thought:
- people put themselves at risk, e.g. living at the foot of steep slopes

Structuralist school of thought:
- stresses constraints on poor people prevailing social and political system of the country
- poor people living in unsafe areas, e.g. on steep slopes of volcanoes, or on floodplains, because they are prevented from living in better areas
- there is a link between environmental hazards and underdevelopment and economic dependency in many developing countries, e.g. hurricane Katrina’s impacts were greater on the poor

38
Q

what are the process of vulnerability

A
  • root causes (ideologies, gender norms, wealth, power, limited access to resources and structures)
  • dynamic pressures (lack of local institutions, rapid population growth)
  • unsafe conditions (dangerous locations, unprotected buildings)
39
Q

what are the economic factors of vulnerability

A
  • levels of wealth influence the quality of housing people live in
  • many people have no option but to live in shanty towns
  • people may have less adherence to building codes and construction styles
  • poorer countries may lack the technology to warn people of upcoming natural hazards
40
Q

what are the social factors of vulnerability

A
  • people with better education generally have higher incomes and can afford better-quality housing and vehicles
  • public education has helped reduce the number of deaths in Japan
  • awareness of hazards
  • gender: women are usually carers for children or parents and may feel responsible for them during an event
41
Q

what are the demographic factors of vulnerability

A
  • population density: larger urban areas pose a higher hazardous risk
  • older people are more prone to risk
  • migrants may be unaware of hazards present in the country
  • people with disabilities with more vulnerable
  • cultural factors: influence public response, i.e. the extent of trust in the government

Geography (10 decks)

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