Mass movements

Question 1

Give a more in depth eg

Answer 1

Vargas mudflows
* Caused by torrential rains and flash floods. Within a 52 hour span, the average rainfall for the entire year fell
* Very flat, fluvial deposits, unconsolidated land. Over-steepened hill slopes failed, providing sediment.
* Flows moved at up to 14.5m/s
* Whole neighborhood of Los Corals buried under 3m of mud
* Unknown death toll, up to 50,000, only 1,000 bodies recovered
* No food or water for months in some areas as remote and poor politics
* Over 70% of population affected
* Much aid was rejected by government

Question 2

Give a more brief eg

Answer 2

Bondo, Switzerland
* In the Alps, a large section of mountain collapsed, leading to a large rockfall, killing 8 hikers initially.
* Lead to a large debris flow.
* Glacial ice melting lead to instability on the mountain walls.
* Debris flow triggered early warning systems so people could evacuate, so nobody in Bondo died.
* Debris flow destroyed bridge and roads, damaged 99 buildings.

Question 3

Hong Kong

Answer 3

• 60% of land is mountainous
• Has a monsoon season, 2,400mm of rain a year
• First place to design and operate a territorial landslide early warning system in 1977
• Focussed on alerting people, also used drainage, afforestation etc
• Since warning system, reduced risk by 50% and nobody has died since 2008
• Climate change and population growth may increase risk, people could get complacent, reduced risk perception

Question 4

Southern California

Answer 4

• Poorly consolidated rock
• Prone to earthquakes
• High rainfall in winter storms
• Oil and water extraction causing ground subsidence
• Rapidly growing population causing construction in hilly districts, cutting into slopes
• 2018 mudflow, aided by forest fire, caused 23 deaths, flowed up to 20mph
• Produced maps showing probability of liquefaction and earthquake triggered landslides, educated, warning systems. Minimal use of physical prevents due to poorly consolidated rock

Question 5

How can you predict and monitor mass movements?

Answer 5

• Often early warning signs, such as cracks, tilted structures, bulging walls.
• Can then monitor when know it is imminent.
• Can be monitored by GPS, which measures distance and direction very accurately.
• Can monitor water content, controlled by drainage pipes.
• Tiltmeters measure tilt occurring.
• Historic records of landslides.
• Tracking weather events.

Question 6

How can you hazard map landslides?

Answer 6

Made using factors affecting slope stability and knowledge of previous movements.
Maps of routes taken by falls, slides or flows may reduce human activity on these paths.