Key Terms and Concepts (1-24) 1. Denudation is the total effect of all actions (weathering, mass wasting, and erosion) that lower the surface of the continents. 2. Weathering- the physical and chemical disintegration of rock that is exposed to the atmosphere. Mass-wasting- the short-distance down slope movement of weathered rock under the direct influence of gravity; also called mass movement. Erosion- detachment, removal, and transportation of fragmented rock material. 3.
Openings in the surface and near- urface bedrock are frequently microscopic, but they may also be large enough to be conspicuous and are sometimes huge. In any case, they occur in vast numbers and provide avenues along which weathering agents can attack the bedrock and break it apart. Subsurface weathering is initiated along these openings, which can be penetrated by such weathering agents such as water, air, and plant roots. As time passes, the weathering effects spread from the immediate vicinity of the openings into the denser rock beyond. . Joints are cracks that develop in bedrock due to tress, but in which there is no appreciable movement parallel to the walls of the joint. Faults are breaks in bedrock along which there is relative displacement of the walls of the crack. 5. Master Joints are Joints that run for great distances through a bedrock structure. Master Joints play a role in topographic development by functioning as a plane of weakness, a plane more susceptible to weathering and erosion than the rock around it. 6.
Mechanical weathering is the physical disintegration of rock material without any change in its chemical composition; also alled physical weathering. Chemical weathering is the chemical decomposition of rock by the alteration of rock-forming minerals. 7. Frost wedging is the fragmentation of rock due to expansion of water that freezes into ice within rock openings. 8. Salt wedging is the rock disintegration caused by the crystallization of salts from evaporating water. 9. Exfoliation is the weathering process in which curved layers peel off bedrock in sheets.
This process commonly occurs in granite and related intrusive rocks after overlying rock has been removed, allowing the body to expand slightly. An exfoliation dome is a large rock mass with a surface confguration that consists of imperfect curves punctured by several partially fractured shells of the surface layers (due to exfoliation). 10. Oxidation is the chemical union of oxygen atoms with atoms from various metallic elements to form new products, which are usually more voluminous, softer, and more easily eroded than the original compounds.
When iron-bearing minerals react with oxygen (become oxidized), iron oxide is produced. This reaction, probably the most common oxidation in the lithosphere, is called rusting. 1 . Hydrolysis- a chemical union of water with another substance to produce a new compound that is nearly always softer and weaker than the original. Carbonation- a process in which carbon dioxide in water reacts with carbonate rocks to produce a very soluble product (calcium bicarbonate), which can readily be removed by runoff or percolation, and which can also be deposited in crystalline from if the water is evaporated. 2. Biological weathering is rock biological weathering is lichens. Lichens are primitive organisms that consist of algae and fungi living as a single unit. Typically they live on bare rock, bare soil, or tree bark. They draw minerals from the rock by ion exchange, and this leaching can weaken the rock. 13. Differential weathering is the process whereby different rocks or parts of the same rock weather and/or erode at different rates. 14. The steepest angle that can be assumed by loose fragments on a slope without downslope movement is called the angle of repose.
This angle, which varies with the nature and internal cohesion of the material, represents a fine balance between the pull of gravity and the cohesion and friction of the rock material. If additional material ccumulates on a debris pile lying on a slope that is near the angle of repose, the newly added material may upset the balance and may cause all of part of the material to slide downward. 15. Rockfall (fall) is the mass wasting process in which weathered rock drops to the foot ofa cliff or steep slope. 16. Talus (scree) are pieces of weathered rock, of various sizes, that fall directly downslope.
Sometimes the fragments accumulate relatively uniformly along the base of the slope, in which case the resultant landform is called a talus slope or talus apron. 17. A talus cone is a sloping, cone-shaped heap of dislodged talus. This cone pattern is commonplace because most steep bedrock slopes and cliffs are seamed by vertical ravines and gullies that funnel the falling rock fragments into piles directly beneath the ravines, usually producing a series of talus cones side by side along the base of the slope or cliff. 18. A rock glacier is an accumulated talus mass that moves slowly but distinctly downslope under its own weight. 9. Landslides do not require the lubricating effects of water or clay, although the presence of water may contribute to the action; many slides are triggered by rains that add weight to already overloaded slopes. Landslides may be activated by other stimuli as well, most notably by earthquakes. 20. A slump is different from other kinds of landslides because it is a slope collapse slide with rotation along a curved sliding plane. 21. A landslide is a general term for a type of slope failure involving an instantaneous collapse of a slope and movement along a generally flat sliding plane.
A mudflow is a rapid, downslope movement of a dense mixture of weathered rock and water through or within a valley. 22. Earthflow is the mass wasting process in which a portion of a water- saturated slope moves a short distance downhill. A debris flow is a stream-like flow of dense, muddy water heavily laden with sediments of various sizes; a mudflow containing large boulders. 23. A soil creep is the slowest and least perceptible form of mass wasting, which consists of a very gradual downhill movement of soil and regolith.
Soil creeps happen slower than a snail can move, and they usually can be prevented if falling towards a house/building. 24. Solifluction is a special form of soil creep in tundra areas; associated with summer thawing of the near-surface portion of permafrost, causing the wet, heavy surface material to sag slowly downslope. Study Questions (1-5) 1. It is possible for weathering to take place beneath the surface of bedrock because of things such as Joints within the rock. If the Joints are deep enough, the weathering will take place underneath certain parts of the rock.
There are many types of a whole, not Just the surface. 2. Chemical weathering is more effective in humid climates than in arid climates because arid climates do not have water. Humid climates have higher amounts of water and higher temperatures so chemical weathering happens faster. 3. There is a direct relationship between gravity and ass wasting. Any mass moves in the direction of the vector sum of all the forces acting on it, with acceleration numerically equal to the magnitude of the sum of the forces divided by its mass.
On or near the Earth’s surface, gravity is always one of the forces. 4. Clay reacts to water by expanding, and when it dries, it contracts. Some clay does it so small that it’s barely noticeable, some clay does it so much that you can very easily see it happen right in front of your eyes. If these clays are in a crack between rock, or in a layer beneath rock, or basically any place that the clay is omehow packed between two hard rocks, and it gets wet, then it will expand, and put force on the two rock layers.
Then it will dry, and “pull” the layer or Joint into a weaker state. If this happens over a long enough time, then it will break the rock that is in the weaker position. 5. Rainfall can expedite mass wasting because when there is more water in the objects that are falling, the objects (falling rocks) become heavier, therefore the process is speeded up. The more rainfall there is, the more water will be accumulated and the heavier the falling rocks will be.
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