Unit 9 - Page 283 - 292

Gabions are commonly used to:

• Prevent floods

• Stabilize slopes and reduce erosion

• Redirect rivers

• Build roads in steep areas

Answer explanation

• Explanation: Gabions (wire cages filled with rocks) hold soil in place and prevent it from sliding downhill.

• Example: In hilly areas, gabions are placed along roadsides to stop landslides and protect vehicles.

Gabions are:

• Large concrete blocks

• Rock-filled wire cages

• Steel beams used in construction

• Plastic nets for soil retention

Answer explanation

• Explanation: Gabions are like strong metal baskets filled with rocks, used to stabilize slopes and absorb pressure from soil movement.

• Example: Gabions are placed near rivers to prevent erosion during floods.

A major trigger for landslides in the Caribbean is:

• Earthquakes

• Prolonged droughts

• Tropical storms with heavy rainfall

• Excessive farming activities

Answer explanation

• Explanation: Rainfall soaks the soil, making it heavy and unstable, causing landslides.

• Example: After hurricanes in the Caribbean, landslides often destroy roads and homes on hillsides.

What is the primary difference between dry and wet avalanches?

• Dry avalanches involve more snow, while wet avalanches involve mud.

• Wet avalanches are slower but denser than dry avalanches.

• Dry avalanches are triggered by rainfall, while wet avalanches are triggered by wind.

• Wet avalanches occur only in coastal regions.

Answer explanation

• Explanation: Wet avalanches have melted snow, so they move slowly but carry more weight. Dry avalanches are fast because they’re made of loose snow.

• Example: A wet avalanche can crush trees and buildings, while a dry avalanche sweeps everything away quickly, like powder.

Gabions are especially effective in reducing:

• Wave erosion in coastal areas

• Water pressure on dams

• Slope instability in mountainous regions

• Earthquake risks

Answer explanation

• Explanation: Gabions are placed on unstable slopes to prevent soil from sliding.

• Example: Engineers use gabions to protect mountain roads from collapsing during rains.

The impact of dry avalanches is primarily due to:

• Their high speed and air pressure

• Their dense, slow-moving flow

• Water saturation in snow

• The lack of vegetation in the area

Answer explanation

• Explanation: Dry avalanches move so fast that the air they push ahead of them creates immense force, causing destruction.

• Example: A skier triggering a dry avalanche could be buried under tons of fast-moving snow in seconds.

Wet avalanches are typically associated with:

• High temperatures melting snow

• Earthquakes in snowy regions

• Wind-driven snow in high-altitude areas

• Heavy rains triggering snowmelt

Answer explanation

• Explanation: When temperatures rise, the snow melts and becomes heavy, causing it to slide downhill.

• Example: Springtime avalanches in the Alps often occur because warmer weather melts the snowpack.

Which of the following human activities can increase the risk of landslides?

• Deforestation on steep slopes

• Building terraces for agriculture

• Using gabions to stabilize soil

• Constructing houses on high ground

Answer explanation

• Explanation: Trees hold soil together with their roots. Cutting down trees makes the soil loose and prone to sliding.

• Example: In areas where forests have been cleared for farming, landslides often happen during rains.

Gabions help prevent landslides by:

• Diverting water flow away from vulnerable areas

• Absorbing seismic vibrations

• Supporting and stabilizing loose soil on slopes

• Blocking falling rocks entirely

Answer explanation

• Explanation: Gabions act like walls to stop soil and rocks from moving.

• Example: On a hillside, gabions can stop soil erosion and keep houses above safe.

Which of the following factors contributes most to dry avalanches?

• Loose snow accumulating on steep slopes

• Heavy rainfall creating waterlogged snow

• Sub-surface cracks in the snowpack

• Rising temperatures during spring

Answer explanation

• Explanation: Loose snow builds up and, if disturbed, quickly slides down a steep slope.

• Example: Skiers or hikers can accidentally cause dry avalanches by stepping on unstable snow.