Mass Wasting involves the movement of rock and soil down a slope due to the force of gravity. Mass wasting can also be referred to as mass movement. There are multiple factors that contribute to mass wasting events. They are water, oversteepened slopes, removal of vegetation, and earthquakes.
Water can interact with gravity to produce mass wasting events. After heavy rains, saturated slopes or hills are heavier and are therefore subject to slope failure. Water can act as a lubricant along the base of the mass movement, filling pores which cause the particles to slide past one another more easily.
If the steepness of a slope exceeds the stable angle, then mass movements become more likely. The steepest slope angle that can be maintained without the potential for downward slipping is called the angle of repose. Depending upon the material, this is 33-37° from the horizontal plane. Slopes that exceed the angle of repose are unstable and are therefore subject to mass wasting. These slopes can be the result of human activity or because of a stream undercutting a valley wall.
Plants’ roots cause slopes to be more stable because of their root system. Therefore once plants are removed the area is more susceptible to mass movements. Earthquakes can move large amounts of rocks and minerals in a short amount of time.
Mass wasting events are generalized according to the kind of material moved, how the material moves, and the speed of movement. The two primary categories of mass wasting events are gradual mass wasting and sudden mass wasting. Gradual mass wasting processes happen very slowly and are often associated with freeze and thaw cycles. They generally do not pose much of a threat to humans since they occur so slowly. Types of gradual mass wasting processes are soil creep and solifluction. Solifluction is the gradual downward sliding of muddy soil over the top of permanently frozen soil below. In soil creep, the force of gravity causes a gradual downward movement of soil particles.
Sudden mass wasting processes occur over a short amount of time. They can be associated with human activities, tectonic activity, or unusually heavy rainfall. Sudden mass wasting processes can occur without warning and can cause a very high loss of life when they occur. The different types of sudden mass wasting processes are often categorized by the amount of water that is present. Read and answer the questions in Mass Wasting and Landslides article.
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Did you know?
Soil creep is the slowest type of mass movement – often moving centimeters per year.
Did you know?
Solufluction is only found in tundra environments when thawing creates a think saturated layer over permafrost.
Did you know?
During a rockfall, rocks or fragments of rocks fall freely through the air. Little of no water is involved in this type of mass wasting event.
Did you know?
In slides, a block of material slides downward along the side of an inclined surface. Some water is involved in this type of mass wasting event. If the block of material is rock, this type of event is called a rockslide. If the block of material is primarily soil and plants, this type of event is called a landslide.
What is the primary force that drives mass movements?
Gravity is the primary force that drives mass movement events.
What is the primary difference between rockslides and rockfalls?
Rockfalls involve rocks or fragments of rocks falling freely through the air. Very little or no water is involved. Rockslide is when a block of material falls down an incline surface. Water is involved.
What are other factors that might contribute to the likelihood of mass movement events occurring?
They are water, oversteepened slopes, removal of vegetation, human activities, and earthquakes.
How do humans contribute to the occurrence of mass wasting events?
Development such as the removal of soil and vegetation (cutting down trees) to build homes, roads, shopping malls, etc.
Compare and contrast gradual and sudden mass wasting events.
Gradual mass wasting processes happen very slowly and are often associated with freeze and thaw cycles. They generally do not pose much of a threat to humans since they occur so slowly. Sudden mass wasting processes occur over a short amount of time. They can be associated with human activities , tectonic activity , or unusually heavy rainfall. Sudden mass wasting processes can occur without warning and can cause a very high loss of life when they occur.
Read through the presentation on mass wasting.
Quiz
What is the primary force that drives mass movements?
Gravity
What is the primary difference between rockslides and rockfalls?
water
What are some other factors that might contribute to the likelihood of mass movement events occurring?
Over steepened slopes, removal of trees or vegetation, flooding, volcanoes, and earthquakes
What is a rockslide?
Rockslides occur when rocks slide downward along a slope, with a large amount of water involved in the process.
What is a rockfall?
Rockfalls occur when whole rocks or bits of rocks fall freely through the air with no or very little involved in the process.
How do humans contribute to the occurrence of mass wasting events?
Uprooting plants, removing vegetation, building roads on mountains, and over-steepening slopes.