EAE 12 - Landslides, Tsunamis and Impacts

Question 1

What are Landslides?

Answer 1

A landslide is a gravity-related slope failure.

Slopes are a consequence of a dynamic planet (landforms change due to tectonic forces).

Over geologic time – slopes are not stable and change constantly.

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Question 2

What is Solifluction?

Answer 2

Downward movement of wet soil along the slopes under the influence of gravity

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Question 3

What is creep?

(In context of Earth movement)

Answer 3

Creep is extremely slow downward movement of dry surficial matter in regions which are subjected to freeze-thaw conditions.

Creep < 2m

Rapid flow ~5m

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Question 4

What is ‘Subsidence due to collapse’?

Answer 4

Subsidence that occurs due to:

• extensive pull out of large volume of underground water
• (In limestone terrain) subsurface solution activity

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Question 5

What is plastic outflow subsidence?

Answer 5

When a plastic layer like clay bed is squeezed outward due to overlying heavy load

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Question 6

What are slump blocks?

2 points.

Answer 6

• Large blocks known as a slump blocks move during a landslide.
• Common
  
  • After earthquakes
  • After removal of part of the slope due to construction (particularly for construction of roads).

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Question 7

What are debris flows?

Answer 7

Debris flows often occur after heavy rain falls.

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Question 8

What are the main factors that contribute to landslides?

6 points.

Answer 8

• Slope
• Water content
• Geological structure
• Unconsolidated or loose sediments
• Lithology
• Human interference

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Question 9

What are triggers for slope failure?

3 points.

Answer 9

The steepness of a slope does not defineits stability.
The geology does.

• shaking grounds (cf. Liquefaction)
• Excess precipitation
• Removal of vegetation can be an additional factor.

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Question 10

How does water impact on stability?

3 points.

Answer 10

Super-saturated sediments will fail.

• Dry sand: friction and cohesion provide shear strength
• Saturated sand: friction and cohesion still sufficient to give the sediment strength.
• Super saturated sand: The fluid supports grains. Shear strength is zero → sediment deforms and fails.

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Question 11

What is the effect of vegetation?

3 points.

Answer 11

• Vegetation gives slopes additional stability
• The effect is critical because water levels are kept lower
• The chance of ‘pore pressure > friction’ is drastically reduced

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Question 12

How are tsunami initiated?

2 points.

Answer 12

A Tsunami is triggered by the sudden displacement of large water masses in the ocean.
The energy is transferred into waves.

• Most frequently: Earthquakes (when the ocean floor is lifted or drops quickly)
• Alternatively: Under-water landslides

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Question 13

What initiates a tsunami?

Answer 13

Water displacement is triggered by an undersea earthquake. A tsunami wave is created (greatly exaggerated). Energy is transmitted from the earthquake into the water.

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Question 14

What happens immediately after a Tsunami is initiated?

Answer 14

The tsunami is split into a distant tsunami and local tsunami with the height of both being each half of the original one.

Both travel in opposite directions. The speed of both tsunamis varies as the square root of the water depth

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Question 15

What happens as a Tsunami progress?

3 points.

Answer 15

The local tsunami will

• reduce in wavelength
• increase in amplitude

There is a trough in front of the tsunami (retrieving water), followed by a strong wave (incoming tidal wave).

The distant tsunami has travelled farther.

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Question 16

What is the tsunami run-up?

4 points.

Answer 16

The tsunami run-up is the waterfront above the normal water level.

• Usually, waves don’t break (unless it is a gigantic tsunami).
• Tsunamis do not stop on landfall and travel far inland.
• The first wave may not be the largest
• Edge waves (think of a fan of waves hitting a straight coastline) result in different travel times.

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Question 17

What are the key dangers of Tsunami?

4 points.

Answer 17

• Tsunami waves do not break – they are continuing waves that travel inland with a continues powerful flow
• Behaivour is similar to the tides (which is a type of wave)
• A critical danger is the retreat of waves, which can carry debris out at sea.
• Tsunamis can come in a series of waves!

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Question 18

What determines the outcome of shooting stars?

Answer 18

Depending on angle of fall (crossing the atmosphere), the object may burn or make it through.

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