Weathering And Mass Movement Pdf
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- Mass Wasting
- 9.2: Mass Movement - Weathering by Gravity and Water
- Slope Erosion and Mass Movement in Relation to Weathering in Geochemical Cycles
- Mass wasting
Rockfalls and rockslides. Rockfalls occur when pieces of rock break loose from a steep rock face or cliff. These result from the rock face being undercut by rivers or wave action. Frost wedging may also eventually loosen large blocks, causing them to fall. The accumulation of rock debris at the base of a steep slope is called talus. Rockslides usually follow a zone of weakness, such as a bedding plane or foliation plane. Separation of the rock is more likely along these planes because of their reduced shear strength.
Another way material can be moved on the coastline is through mass movement. Mass movement is the downhill movement of sediment that moves because of gravity. There are four different types of mass movement:. Bits of rock fall off the cliff face, usually due to freeze-thaw weathering. Saturated soil soil filled with water flows down a slope. Large blocks of rock slide downhill.
The crust of the earth is raised or depressed with respect to the geoid by endogene phenomena associated with epeirogeny and orogeny. These large-scale crustal movements come within the province of tectonics and are not considered here. The surface layers of the crust are subject in addition to the action of exogene processes, largely controlled by climate, of which weathering, mass movement and mass transport are the chief. These interact with the endogene processes to produce surface form. Weathering results in most cases in a weakening of a surface zone of the crust, rendering it more susceptible to downward movement under the influence of gravity. Mass movement comprises all such gravity-induced movements except those in which the material is carried directly by transporting media such as ice, snow, water or air, when the process is termed mass transport.
9.2: Mass Movement - Weathering by Gravity and Water
Mass wasting , also known as slope movement or mass movement , is the geomorphic process by which soil , sand , regolith , and rock move downslope typically as a solid , continuous or discontinuous mass, largely under the force of gravity , frequently with characteristics of a flow as in debris flows and mudflows. Mass wasting occurs on both terrestrial and submarine slopes, and has been observed on Earth , Mars , Venus and Jupiter's moons Io and Ganymede. When the gravitational force acting on a slope exceeds its resisting force, slope failure mass wasting occurs. The slope material's strength and cohesion and the amount of internal friction within the material help maintain the slope's stability and are known collectively as the slope's shear strength. The steepest angle that a cohesionless slope can maintain without losing its stability is known as its angle of repose. When a slope made of loose material possesses this angle, its shear strength counterbalances the force of gravity acting upon it.
In chapter 5 you read about sink holes, one form of weathering by water and gravity. Sink holes form what is known as Karst Topography , which has the effect of making the landscape appear pockmarked. Karst topography results from the chemical weathering of limestone underground, and the action of gravity forcing the overlying earth to fill in the void. You might want to look for examples of topographic maps of karst topography in the central United States one example of water-gravity weathering or other places in the world. Another, more common example of weathering by water and gravity is mass movement or landslides. Mass movement occurs when soil is saturated with water, which makes it heavy, and the force of gravity overcomes the resistance of the slope.
In this section, you will learn the term mass wasting. You will also be exposed to the various types of mass wasting, their causes and their effects. Figure 1. Pieces of rock regularly fall to the base of cliffs to form talus slopes. Rocks that fall to the base of a cliff make a talus slope figure 1. Sometimes as one rock falls, it hits another rock, which hits another rock, and begins a landslide. Landslides and avalanches are the most dramatic, sudden, and dangerous examples of earth materials moved by gravity.
Slope Erosion and Mass Movement in Relation to Weathering in Geochemical Cycles
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Geomorphic models of slope development and hydrologic models of runoff generation are reviewed in order to identify the major processes of interest. Slope erosion and mass movement are then classified and typical rates of operation identified. Rates of weathering are also reviewed. The main purpose of the chapter is to identify the sediment and solute budget approach as the best way to understand the relative roles of slope erosion, mass movement and weathering in relation to geochemical cycles. Major problems that have been encountered in the quantification of sediment and solute budgets are discussed.
Mass wasting is the movement of rock and soil down slope under the influence of gravity. Rock falls, slumps, and debris flows are all examples of mass wasting. Often lubricated by rainfall or agitated by seismic activity, these events may occur very rapidly and move as a flow. Landslide triggers may include:. The runout of a mass wasting event depends on the volume of material, water content, and slope steepness. A Debris Flow is a type of landslide made up of a mixture of water-saturated rock debris and soil with a consistency similar to wet cement.
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Ch 16 Weathering, Erosion and mass wasting. 1. Rock Cycle, weathering, and erosion. 2. Mechanical weathering. 3. Chemical Weathering. 4. Soil. 5.