Hazards Resulting From Mass Movements

Question 1

Explain two causes of landslides other than earthquakes

Answer 1

• Human activity such as deforestation reducing binding of particles. For example in Vargas, Venezuela December 1999 the landslide was caused from the slopes of the Sierra de Avila mountains being heavily deforested. As a result the slopes lost their protection and stability because trees had been cleared by local people. Therefore making it susceptible to landslides.
• Reduction in friction between particles from heavy rainfall. For example in Vargas, Venezuela December 1999 was very wet, as 911mm fell in 52 hours, equivalent to a year’s average rainfall.

Question 2

Suggest how mudflows are formed

Answer 2

• Mudflows need a source of water which can come from snow/ice cover melting due to lava heat
• Volcanic eruption at Mount Rainier occurs at/near the top of the cone
• Meltwater generated combines with volcanic ash and/or mud/snow to create a mudflow
• Water reduces cohesion and increases weight
- Earthquake trigger as well as swelling of volcano during eruption
• Mudflows travel under gravity, usually following valleys towards Puget Sound lowland or other low points in the landscape

Question 3

Explain two reasons why the number of deaths from mass movement events varies.

Answer 3

The type of mass movement. Some types of mass movements, such as mudslides are more likely to cause fatalities than others. This is because they can travel faster and farther, and they can carry more debris. For example, Venezuelan mudslides in 1999 killed 30,000 people. In contrast the 2010 China landslide killed 1122 people because the landslides are typically slower moving and less destructive.

• The location of the mass movement. For example The Venezuelan mudslides occurred in Vargas which is a densely populated area, which is why they caused so many deaths. The China landslide on the other hand occurred in a small town Zhouqu which is a more rural area.

Question 4

How are lahars formed

Answer 4

• Formed when volcanic debris such as ash absorbs water and loses its internal strength. Heat from volcanoes melts snow and ice - resulting flow picks up sediment and forms a lahar.
• A good example is Nevada del Ruiz, Colombia. In 1985 the eruption melted the summit snow and glaciers, condensing volcanic steam and pyroclastic flows to form lahars moving 60km/hr down the mountain.

Question 5

How are rock falls formed

Answer 5

• An example is Bingham copper mine rock fall, USA. 135 million tons of rock fell into an open pit as a result of solid bedrock breaking away from the upper half of the slope, together with waste from the mine that piled up above it. Thus putting additional stress on the slope. The rock slid down the shear plan, before free falling into the pit.

Question 6

Explain why the hazardous nature of the type of mass movements varies

Answer 6

• Mudflows will quickly cover longer distances therefore more hazardous. For example, the mudflow that occurred in Oso, Washington in 2014 travelled 2.4km while killing 43 people and destroying over 30 homes.
• Landslides can also be very hazardous, especially if they occur in populated areas. Landslides can block roads and railways, and they can also damage or destroy buildings. For example, the landslide that occurred in the city of Chatsworth, California in 2005 killed 19 people and caused over $1 billion in damage.

Question 7

What are the impacts of live and property of a mass movement?

Answer 7

• Loss of life: Mass movements can cause fatalities both directly and indirectly. People may be killed by falling rocks or debris, or they could drown in flash floods or be buried in landslides.
• Damage to infrastructure: Mass movements can damage roads, bridges, buildings, and other structures, disrupting transportation and communication networks.
• Soil erosion: In mountainous areas, mass movements can lead to soil erosion, which can reduce the fertility of the soil and affect the availability of water.