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A Level Physical Geography > Hazards- Volcanoes > Flashcards

Hazards- Volcanoes Flashcards

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1
Q

Shield volcanoes

A
  • gentle slopes and wide base
  • frequent eruptions of basaltic lava
  • lava flows at high speeds and for long distances before cooling
  • usually non violent eruptions
  • non viscous lava due to basaltic composition
  • found at constructive boundaries
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2
Q

Composite volcanoes

A
  • steep sided with a cone shape
  • high with narrow base
  • explosive eruptions of lava and ash
  • viscous lava builds in layers and does not flow far from the crater
  • found at destructive boundaries
  • secondary cones formed when the main vent gets blocked
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3
Q

Icelandic volcanoes

A
  • low viscosity and highly effusive

- may have water therefore phreatic

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4
Q

Hawaiian volcanoes

A

-effusive, minor explosivity, with fire fountain and low viscosity lava flow

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5
Q

Strombolian volcanoes

A

Eruption with gas bubbles so ejects tephra (ash and lapilli)

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6
Q

Vulcanian volcanoes

A
  • higher gas build up than Strombolian, highly viscous lava

- a series of short lived explosions with tephra including bombs

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7
Q

Pelean volcanoes

A

-explosive eruptions with a range of tephra with nuee ardent (glowing cloud) pyroclastic flows

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8
Q

Plinian volcanoes

A
  • highly explosive, large eruption columns (up to 45km)

- range of tephra and pyroclastic fallout (including flows)

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9
Q

The Volcano Explosivity Index (VEI)

A
  • scale used to measure intensity of volcanic eruptions
  • similar to the Richter scale and Mercalli scale
  • VEI measures explosivity, volume of ash (tephra) and the height ash reaches into the atmosphere
  • it also gives a description and name of the eruption and the total no. of those eruptions in human history
  • allows die comparison between events
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10
Q

Lahars

A
  • mixture of hot/cold water and rock fragments
  • form when erupted volcanic material gets saturated during periods of heavy rainfall
  • may be some time after an eruption
  • can grow as they travel (picking up material)
  • most common on strato-volcanoes (steep gradient required)
  • capable of setting like concrete
  • can destroy anything in their path
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11
Q

Mudflows

A
  • consist of flows of ash, cinder, soil and rock
  • changed into clay by acids in volcanic gases
  • can be hot or cold depending on origin including:
    • eruptions effecting water directly
    • rapid snow/ice melt
    • eruption induced by heavy rainfall
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12
Q

Tephra

A

-rocks ejected up into the atmosphere
-largest pieces called blocks
-often fall near to the site
-small particles called lapilli- remain in atmosphere for years
-moving away from volcano particles get smaller
-thickening occurs when ash+water join
Distance tephra travels affected by:
-temperature of air
-wind direction/speed
-height of eruption column

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13
Q

Nuées Andentes

A
  • a huge cloud of ash
  • relatively cool (compared to pyroclastic flows)
  • linked with Plinian and Vulcanian activity
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14
Q

Lava flow

A
  • effected by the type of lava
  • as the thickness of lava increases- viscosity increases
  • this makes the lava flow slower
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15
Q

Gases

A
  • consists mainly of water vapour
  • remaining gases include CO2, SO2, H, N, Ar
  • hydrogen and water combine with other elements to produce toxic compounds eg. Hydrochloric acid
  • volcanoes emit gas even when they’re not erupting
  • increase of levels of gas indicates an eruption in near future
  • thermal imaging camera and gas samples used
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16
Q

Acid rain

A
  • SO2 emissions can result in acid rain and air pollution downwind of the volcano
  • acid rain can cause health problems
  • SO2 can be ejected more than 10km into the air
  • SO2 becomes sulphate aerosols- reflect sunlight and have a cooling effect on Earths climate
  • makes soil acidic- can reduce crop yield
17
Q

Ash fallout

A
  • clouds of ash moved by the wind
  • known as ash plumes
  • move away from the volcano vent (no longer supported by gases)
  • unsupported particles fall out
  • ash deposits thicken near the vent
  • if there’s heavy rainfall ash can form volcanic mudflows
18
Q

Pyroclastic flows

A
  • fast moving currents of hot gas and rock
  • can reach up to 1000 degrees
  • one of the most dangerous-destroy everything in path
  • high density mix of hot lava blocks, pumice, ash and volcanic gas
  • move at high speed
  • consist of lower flow and a turbulent cloud of ash
  • formed by collapse of eruption columns/lava domes due to them becoming too steep
19
Q

Monitoring volcanoes- geological observations

A
  • topography measured to detect ground movements that occur when a volcano is active
  • tiltmeter used to measure change in slope angle of a volcano
  • installed when the volcano is relatively inactive
  • when magma rises the volcano expands-tiltmeter measures this
  • horizontal movements using GPS
20
Q

Monitoring volcanoes- seismic activity

A
  • occurs as volcanoes prepare to erupt
  • increase in activity may indicate its likely to erupt
  • type of earthquakes that occur are also key
  • measured by seismographs
  • infra sound also monitored to detect and locate eruptions
  • difficult to distinguish between plate movements and seismic activity
21
Q

Monitoring volcanoes- gas emissions

A
  • increasing amounts of SO2 indicate increasing amounts of magma near the surface
  • sometimes levels drop prior to eruptions (harden f magma seals gas passages)
  • emissions measured at the volcano (in the crater) by helicopter
22
Q

Protection/preparation on an individual level

A
  • avoid river areas and low lying land
  • close windows and stay indoors and block chimneys
  • ash should be swept off roofs
  • avoid driving as ash can damage engines
23
Q

Protection/preparation on a government level

A
  • lava cooled by water which turns into steam allowing the lavas heat to dissipate
  • build a barrier to prevent the lava flows from reaching major towns/cities
  • artificial trenches built in order to divert flow, then concrete blocks are added to fully divert and stop the flow (MICs only)

A Level Physical Geography (26 decks)

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