Mass Wasting

Mass Wasting Mass wasting is the down-slope movement of rock and soil under the pull of gravity. Individual rocks may break away and slide down slopes, or whole sections may collapse into landslides. Factors: Steepness of slope Shape and size of particles Nature of ground cover Water content of the soil

When water seeps into soil, the soil expands and becomes heavier. The expansion of the soil moves the particles of soil and makes the slope less stable. Processes and changes that make the soil particles less compacted can make the slope less stable. Vegetation is an important part of slope stability. The roots act as anchors and hold the soil together. When plants are removed the soil can become less stable.

Human actions such as cutting down trees and building roads often lead to unstable slopes. Paving large areas can also lead to unstable slopes. Water cannot drain through concrete, leading to pooling and flash floods.

How can we stabilize slopes? This is especially an issue in places like BC where many roads are cut into hills and rock falls are a major safety issue. Often retaining walls of stone or concrete are built to support the slope. A wire mesh or layer of concrete attached to the slope can help provide stability. Terracing can be used to support slopes as well. In areas with heavy snowfall, snowsheds can protect roads from avalanches (large slides of snow)

Ways of Preventing

1) Slope Failure Slope failure is the collapse of rock or sediment mass. 3 major types of slope failure: Slumps. Falls. Slides. Key factors are steepness of slope, composition of soil, amount of water

Slumps Section of land breaks away and slips a short distance. The top layer of soil stays intact.

Rock/Debris Fall The free falling of rocks or debris from a slope. Often in very steep locations. This is often caused by frost shatter. The rocks collect at the bottom of the mountain/slope and are called scree or talus

Rock/Debris Slide The rapid movement of rocks/soil down a slope. If it is mostly rock= rock slide If there is also plant matter and soil =debris slide or landslide Usually lesser slope than a rock fall

Snow or Debris Avalanches A huge mass of falling snow + ice or rock + debris that breaks away and slides down a slope. Often started by earthquakes + volcanoes, winds, or even people!

2) Sediment Flows Process where soil receives so much water that it flows down a slope – almost like a river. Earthflow – break away at slope then flow slowly. Vegetation stays together. Mudflow – more intense, much faster, and everything mixes together

Earthflows

Creep Creep is a very slow type of flow. Usually found on gentle slopes. Affected mostly by gravity