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Hazards resulting from mass movements?
Terms in this set (18)
What are the hazards that come from a mass movement?
-Amount of water; lahars can wipeout + destroy homes.
-Material involved in movement; destruction of infrastructure, belongings, crushing people and destroying farm land when deposited.
-Speed of the movement; can be unexpected and unpredictable = little time to prepare or prevent damage.
-The type of movement; fall, slide, flow, slump
What is a fall?
A spontaneous and rare debris movement, that occurs as a result of extreme physical and chemical weathering at the base of a cliff. rock falls = scars and talus builds up.
What is a slide?
A rapid movement where material moves in a straight line down a slope in one uniform piece, as it becomes detached from the bedding plane. Rotational slide = steps with planes that point upwards.
What are flows?
Faster movements that occur on steeply sided slope and involve more water and can occur as large amounts of rainfall infiltrate into the regolith, causing the slope to be undermined be the added sheer stress. They are often more dense and viscous, carrying more suspended material.
How can mass movements be predicted? What are the strengths and weaknesses?
Through slope stability analysis which takes into account angle + weight of material balances + friction, gravity and uses maths to assess and identify dangerous slopes.
-Makes people aware of where slopes are bad = no building.
-Geology not fully understood. Skilled and expensive. Very high-tech.
How can mass movements be mapped? What are the strengths and weaknesses?
Through landslide hazards analysis where drones map direction in which material falls.
-Reduces hazard of future movement = mapping and education.
-Doesn't protect land and only collects data for advise.
How can mass movements be monitored?
E.g. slope safety system in Hong Kong.
Cataloged of data collected of dangerous slopes, land, owners can be fined.
-effective information and incentivises land owners.
-does not prevent of protect. -expensive to pay people to monitor slopes.
How can slopes be stabilized to prevent movements?
Retaining walls, tunnels, drainage pipes, afforestation, shotcrete, gabions, pinning, cliff regrading. Some prevent water from getting into regolith = no sheer stress. Other are expensive and very drastic to the landscape. Some take time to be effective in stabilising slopes.
What are the human impacts on the hazards of mass movements?
-Education is lacking = perception of risk is low = more people may live near slope.
-corruption = building regulations are not policed or no regulations at all.
-Preparedness = weak infrastructure and housing with poor foundations = easily wiped out.
-Deforestation and pressure on land = infiltration of water (Aberfan).
What were the causes of the mud and rock slide in the Val Bondasca region in east Switzerland in 2017? What were the impacts on lives/ property?
Melting permafrost, alpine lake overflows, rock structure with lots of joints, a period of heavy rain. 8 people killed, 12 farm buildings along the 5km distance material travelled destroyed.
How were the people in the town of Bondo prepared and what is their perception of risk? What are the impacts of this approach? what may happen in the future? (climate change)
Warning sirens fitted in 2012, roads were automatically closed. Don't build near where movements take place, locals know what to do = fewer at risk and in danger.
Climate change = more rain = more movements = more spent on warning systems.
What was the nature and causes of the Sierra Leone Landslide in the town of Freetown in 2017?
3 times more rain than usual in recent weeks, deforestation, informal settlements and corruption allowing development of housing on unstable slope. Climate increased rate of chemical weathering on the slope. Large amounts of material removed a large area of slope
What were the impacts of the Freetown landslide on lives and property?
over 1000 killed, trapped and buried alive, Cholera and Typhoid outbreak due to sewerage mixing with drinking water, 7000 displaces. people had to be dug out with bare hands with the help of the military which was deployed.
How did the preparedness and perception of risk play a factor in expanding the impact of hazards? what is the future?
Monitoring of slope does not take place = cannot afford it. No warnings were issued after period of intense rain. People did not think they were at risk. Population growth = development of more housing
What were the causes of the Hong Kong landslide, along Po Shan road which killed 68?
Hot climates = chemical weathering = chemical weathering = deeper regolith. Up to 400 mm of rainfall per month equals pore pressure = sheer stress. Gradient of 30 in some places = large amounts of sheer stress. One of the most densely populated places in the world, excavation of slopes to build large high-rise apartment buildings = very little sheer strength. = wiped out.
What was the Slope safety system introduced in Hong Kong? What are its pros and cons?
introduced by department of geological affair who regularly asses slope and can fined private slope owners for not assessing. Keeps catalogue of slopes to say how safe they are.
+Makes people aware of slope and natural disaster, risk of landslide is reduced by 50%, jobs for monitoring.
-All 57,000 slopes in HK cannot be monitored at once. assessment can delay development of slopes. Expensive.
What are the drainage channels in HK? What are their pros and cons?
Channels diverge water away from weaker points that are reinforced with materials that prevent infiltration and addition of sheer stress.
+Diverges water away quickly, prevents infiltration into regolith.
-Drains are vulnerable to blockage and overflowing.
What are the methods of vegetation growth used on the slopes in Hong Kong? What are its pros and cons?
Drilling planter holes to allow long-rooted vegetation to grow. Mulching system = protective cover allows vegetation to grow.
+Natural, environmentally friendly, high water retention capacity.
-Takes time, expensive, too much vegetation can add sheer stress onto slope.
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