volcanic and slope failure-landslide hazards

Question 1

what are examples of volcanic hazards? (7)

Answer 1

• 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.

Question 2

what is lava flow?

Answer 2

• Molten rock or magma erupting at the surface

* Composition and temperature controls behaviour of lava flows

Question 3

what are balsaltic properties?

Answer 3

Basaltic/mafic- low viscosity, flows fast

Question 4

what are silicic properties?

Answer 4

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

Question 5

why is lava flow destructive?

Answer 5

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

Question 6

what is tephra?

Answer 6

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

Question 7

what are the hazards of ash fall?

Answer 7

• 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)

Question 8

what are ballistic explosions?

Answer 8

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

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

Question 9

where are explosive eruptions most commom?

Answer 9

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

Question 10

how can a volcano trigger an explosion?

Answer 10

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

Question 11

what happened at Mt St Helens?

Answer 11

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.

Question 12

what are pyroclastic flows?

Answer 12

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

Question 13

what are lahars or mud flows?

Answer 13

• 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.

Question 14

what are the temperature and speed of pyroclastic flows?

Answer 14

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

Question 15

where do lahars originate from?

Answer 15

Originate on slopes of volcano

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

Question 16

what is the speed of lahars?

Answer 16

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

Question 17

what can also cause a lahar?

Answer 17

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

Question 18

waht gas emissions are dangerous with a volcano?

Answer 18

• 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

Question 19

what are aerosols?

Answer 19

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

Question 20

what is a consequence of gas emissions?

Answer 20

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

Question 21

what are fumaroles?

Answer 21

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

Question 22

what is slope failure?

Answer 22

• 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.

Question 23

what are submarine slope failures?

Answer 23

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.

Question 24

what are subaerial slope failures?

Answer 24

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

Question 25

what are mitigations of volcanoes?

Answer 25

• 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.

Question 26

how are the tsunamis measured?

Answer 26

• Tsunami size defined by intial landslide parameters

Question 27

what is a worse case model?

Answer 27

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

Question 28

what is the mode of failure?

Answer 28

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

Question 29

how can models casue tsunamis?

Answer 29

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

Question 30

what analysis from El Hierro landslide?

Answer 30

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