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Mass Movement Flashcards

1
Q

Define Mass Movement

A

Process by which material moves down a slope under the influence of gravity. The material can include rocks, stones, soil and mud (regolith)

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2
Q

Where do landslides occur?

A

Mountainous areas and coastlines

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3
Q

Do natural processes, tectonic activity or human activity cause solifluction

A

Natural processes

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4
Q

How fast can lahars travel on steep slopes?

A

100 km/h

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5
Q

Do natural processes, tectonic activity or human activity cause slumping?

A

Natural processes and human activity

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6
Q

Define human activity

A

Construction, deforestation and road building can increase the risk of mass movement

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7
Q

Define gradient

A

The steepness of a slope, affecting how quickly the material moves

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8
Q

What speed is earthflow?

A

Moderate

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9
Q

Causes of earthflow

A
  • Heavy rainfall means water unable to percolate through rock causing soil to be saturated
  • Loses friction with underlying rock and flows downslope
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10
Q

What speed are avalanches?

A

Fast

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11
Q

Define lahar

A

Volcanic mudflow

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12
Q

Define water content

A

The amount of water in the soil, which can increase movement by acting as a lubricant

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13
Q

Define soil creep

A

The slow movement of soil down a slope, often causing trees and fences to tilt

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14
Q

Do natural processes, tectonic activity or human activity cause earthflow?

A

Natural processes

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15
Q

How fast can lahars travel on gentle slopes?

A

20 km/h

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16
Q

Do natural processes, tectonic activity or human activity cause mudflows?

A

Natural processes and human activity

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17
Q

Define rockfall

A

The sudden fall of rocks from a steep cliff or slope, usually due to weathering

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18
Q

Define regolith

A

Loose rock, soil, and debris that covers the earth’s surface

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19
Q

Do natural processes, tectonic activity or human activity cause lahars?

A

Tectonic activity

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20
Q

Do natural processes, tectonic activity or human activity cause bogbursts?

A

Natural processes and human activity

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21
Q

Where does soil creep occur?

A

Gentle slops of 10° to 15°

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22
Q

Where does solifluction occur?

A

Higher ground where soil is frozen

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23
Q

Identify different types of mass movement from diagrams

A

N/A

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24
Q

What causes soil creep?

A

Freeze thaw action:
* Freezing of land in upland areas
* Soil expands due to water absorption
* Soil contracts when water melts
* Soil moves slowly downslope

Wet dry cycles:

25
Define lahar
A destructive mudflow on the slopes of a volcano, often triggered by volcanic activity and heavy rainfall
26
Where does rockfall occur?
Very steep/vertical slopes
27
Do natural processes, tectonic activity or human activity cause rockfall?
Natural processes and human activity
28
Do natural processes, tectonic activity or human activity cause avalanches
Natural processes, human activity and tectonic activity
29
Feature of rockfall
Scree fields - largest pieces of scree travel furthest downslope
30
What speed are lahars?
Fast
31
What speed is solifluction?
Slow
32
What speed is mudflow?
Fast
33
Do natural processes, tectonic activity or human activity cause landslides?
Natural processes, tectonic activity and human activity
34
What speed are bogbursts?
Fast
35
Where and when does earthflow occur?
Hills after heavy rainfall where regolith lies over impermeable rock or when forestry removed from hillside
36
Features of earthflow
* Small bulges on landscape * Torn vegetation
37
Causes of rockfall
**Freeze thaw action:** Enlarges cracks and joints, causing pieces of solid rock to break free and fall down slope
38
How fast is soil creep?
0.5cm per annum
39
Where does slumping occur?
Steep slopes made of unconsolidated material eg. boulder clay
40
Define mudflows
Occur when saturated soil and mud flow rapidly down a slope, often after heavy rainfall
41
What speed is soil creep?
Slow
42
What speed is rockfall?
Fast
43
What effect does vegetation have on mass movement
Plant roots help to stabilize the soil and prevent mass movement
44
What speed are landslides?
Fast
45
Define landslides
A sudden, rapid movement of large amounts of rock and soil down a slope
46
Give details on a lahar case studies
**Nevado del Ruiz** * Nevado del Ruiz, Colombia erupted on November 13th, 1985 after 69 years of dormancy * Pyroclastic flows melted the mountains glaciers causing four lahars moving downslope at 50 km/h * They destroyed the town of Armero, killing 20,000 of its 29,000 inhabitants * Volcanological organisations had warned the government to evacuate the area two months prior but the government had not listened * Relief efforts were hindered by the composition of mud which made it difficult to move through **Mt Pinatubo, Philippines, 1991** * Heavy rain mixed with ash deposits from the eruption * Lahars travelled over 50km destroying everything in their path * Lahars occured for years after eruptions
47
Features of solifluction
Small, thin folds of soil
48
Define avalanche
A rapid flow of snow and ice down a mountainside, which can be triggered by weather conditions or human activity
49
What causes solifluction?
* During summer, soil close to surface thaws and soil underneath stays frozen * During rainfall, thawed soil becomes water saturated and unable to percolate through permafrost below * Moves slowly downslope due to gravity
50
Define bog bursts
Happen in upland areas when peat becomes saturated with water and moves downslope quickly
51
Causes of landslides
1. * Fractures along bedding planes cause rock to dip downward * Loose regolith an top slides off Water reduces friction between regolith and rock and adds weight causing regolith to move faster downslope 2. Coastal erosion 3. Seismic activity
52
Feature of slumping
Steep, crescent shaped cliff formed at upper point of slope
53
Define terracettes
A series of ridges that run across a hill formed from the slow, downward movement of soil
54
Explain some triggers of lahars
* Volcanic eruptions: Volcanoes have glacial ice at top. Volcanic eruption rapidly melts this ice. Water mixes with volcanic debris * Intense rainfall on volcanic deposits: Tropical rainfall (eg. Philippines) mixed with ash - deadly mudflow * Collapse of volcanic lake/crater: Sudden release of large amounts of water - mixes with debris
55
Do natural processes, tectonic activity or human activity cause soil creep
Natural processes
56
Cause of slumping
* Base of slope removed due to road construction or natural processes at coastlines/riverbanks * Causes large block of regolith above it to slide downwards due to gravity
57
Features of soil creep
* Terracettes: Ridges in upper layers of soil - most movement occurs in top soil layer * Trees at angles * Walls and fences leaning
58
Explain some factors affecting mass movement
* Gradient: The steeper the slope, the faster the material will move due to gravity * Water content: Water makes the soil heavier and acts as a lubricant, increasing the likelihood of movement * Vegetation: Plant roots help to bind the soil together, reducing the risk of mass movement * Human activity: Activities such as deforestation and road construction can destabilize slopes and trigger movement * Rock type: Some rocks, like clay, become unstable when wet, leading to increased movement * Climate: Areas with heavy rainfall experience more frequent mass movement due to water saturation
59
What speed is slumping?
Moderate

Geography (12 decks)

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