volcanic and slope failure-landslide hazards Flashcards

1
Q

what are examples of volcanic hazards? (7)

A
  • Lava flows
    • Ash falls and other ejecta (tephra)
    • Ballistics (explosions and blasts)
    • Pyroclastic flows
    • Debris avalanches and landslides
    • Lahars or mud flows- tend to follow the eruptions.
    • Gas emissions. Less of a hazard, but assessing the eruption.
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2
Q

what is lava flow?

A
  • Molten rock or magma erupting at the surface

* Composition and temperature controls behaviour of lava flows

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3
Q

what are balsaltic properties?

A

Basaltic/mafic- low viscosity, flows fast

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4
Q

what are silicic properties?

A

Silicic/felsic- high velocity, flows slowly. Leads to more violent eruptions.

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5
Q

why is lava flow destructive?

A

Destructive due to high temperatures but in many cases flows slowly enough or on predictable paths for people to escape.

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6
Q

what is tephra?

A

• Tephra- anything ejected out of a volcano. Ash is defined as smaller than 2.5 mm. Other terms include lapilli, blocks, and bombs.

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7
Q

what are the hazards of ash fall?

A
  • Weight of the ash can cause damage to structures
    • Hazards to flying aircrafts
    • Visibility hazard
    • Abrasive material, corrodes.
    • Electronics, machinery, power generation, telecoms.
    • Proximal burial
    • Inhalation
    • Transported far from volcano so can affect a large area dependent on the wind direction.
    • Large eruptions can impact climate (local or global)
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8
Q

what are ballistic explosions?

A
  • Vertical or lateral explosions of debris, magma, gas.

* Can lead to pyroclastic flows, mud flows, debris avalanches, landslides, ash falls etc.

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9
Q

where are explosive eruptions most commom?

A

Explosive eruptions are more common for silicic magmas (continental), or underwater eruptions

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10
Q

how can a volcano trigger an explosion?

A

Volcanic eruption, earthquake (indirectly), or landslide can trigger an explosion.

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11
Q

what happened at Mt St Helens?

A

Mt St Helens- an earthquake triggered a landslide which released pressure leading to an unexpected lateral blast.
Includes individual bombs, blocks etc. Now Helens has a huge gap where the landslide occurred.

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12
Q

what are pyroclastic flows?

A
  • High speed avalanches of hot ash, rock and gas.
    • During explosive eruptions
    • Destroys everything in their path.
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13
Q

what are lahars or mud flows?

A
  • Dilute downstream
    • Often triggered by rain fall or landslides during or following an eruption
    • Can occur between eruptions
    • More distal nature and delay increase hazard and risk.
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14
Q

what are the temperature and speed of pyroclastic flows?

A

• Temperature up to 1500 degrees celcius. 150-250 km/h.

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15
Q

where do lahars originate from?

A

Originate on slopes of volcano

• Water saturated debris, high percentage of rock and ash debris

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16
Q

what is the speed of lahars?

A

Flow rates up to 10 metres per second. Can travel 100 km from volcano dependent on travel networks

17
Q

what can also cause a lahar?

A

• Slow melt or water trapped beneath ice may also lead to lahar

18
Q

waht gas emissions are dangerous with a volcano?

A

• All magmatic materials contain dissolved gases- water, CO2, SO2, H2S.

* Change in gas emission scan be used to predict eruptions 
* SO2 can lead to acid rain
19
Q

what are aerosols?

A

• Aerosols in atmosphere can affect earths surface temperature, destroy ozone.

20
Q

what is a consequence of gas emissions?

A

Close to vents- hazardous to humans and livestock- potential suffocation
• Local and downwind corrosion

21
Q

what are fumaroles?

A

Long term “fumarole” systems emit gas on most active volcanoes, and for 1000’s year post eruption.

22
Q

what is slope failure?

A

• Takes many forms both on land and offshore- rock falls, avalanches, debris flows, turbidity currents. All involve different quantities of debris and fluid, different flow types/processes.

23
Q

what are submarine slope failures?

A

Submarine slope failures: can be triggered by earthquakes, can generate tsunami waves, but dissipate rapidly, can result from collapse of steep slopes, such as marine volcanic islands such as Hawaii.

24
Q

what are subaerial slope failures?

A

Subaerial slope failure: similar triggering mechanisms. Rainfall, high runoff, coastal erosion increase probability.

25
Q

what are mitigations of volcanoes?

A
  • Understand geology and past failure history. Failure planes, rock and sediment permeability versus overpressure.
    • Improving slope stability (engineering)
    • Controlling water flow and sediment saturation
    • Controlling runoff, deforestation, development, fire. Can use drains, mesh traps, vegetation on the slopes., spray cement.
    • Assessing timing of triggering events
    • Adapting building codes and development or planning.
26
Q

how are the tsunamis measured?

A

• Tsunami size defined by intial landslide parameters

27
Q

what is a worse case model?

A

Worst-case models assume failures are very large, entire landslides fails as a single coherent block, and landslides reaches high peak velocity.

28
Q

what is the mode of failure?

A

• The mode of failure is critical for whether a tsunami is generated and for its magnitude

29
Q

how can models casue tsunamis?

A

• Models with above parameters can result in large tsunamis than can cause destruction on ocean basin scale.

30
Q

what analysis from El Hierro landslide?

A

• Analysis of seafloor bathmetry and of marine sediment cores reveals: landslide processes range from avalanches to debris flow