Charmaine Farrah Estacio
Dr. Thomas Orf
11th November 2014
ASSIGNMENT: CHAPTER 15
PRELIMINARIES TO EROSION: WEATHERING AND MASS WASTING
KEY TERMS AND CONCEPTS:
1. What is meant by denudation?
The total effect of all actions (weathering, mass wasting, and erosion) that lower the surface of the continents.
2. Distinguish among weathering, mass wasting, and erosion.
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 influence of gravity; also called mass movement. Erosion- is the detachment, removal and transportation of fragmented rock material.
3. What roles do rock openings play in weathering processes? Whenever bedrock is exposed, it weathers. Weathered rock often has a different color or texture from neighboring unexposed bedrock. Most significant from a topographic standpoint, exposed bedrock is likely to be looser than the underlying rock. Blocks or chips maybe so loose that they can be detached with little effort. Sometimes pieces are so “rotten” that they can be crumbled by finger pressure. Slightly deeper in the bedrock, there is firmer, more solid rock, although along cracks or crevices weathering may extend to considerable depths. In some cases, the weathering may reach as much as several hundred meters beneath the surface. This penetration is made possible by open spaces in the rock bodies and even between the mineral grains. Subsurface weathering is initiated along these openings, which can be penetrated by such weathering agents 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.
4. What is difference between a joint and a fault?
Joints- Cracks that develop in the bedrock due to stress, but in which there is no appreciable movement parallel to the walls of the joint. Fault- A fracture or zone of fracture where the rock structure is forcefully broken and one side is displaced relative to the other. The movement can be horizontal or vertical, or a combination of both.
5. What are master joints, and how can they influence the topography landscape? In some places, large joints or joint sets extend for long distances and through a considerable thickness of rocks; these are termed master joints. Master joints roles in topographic develop by functioning as plane of weakness, a plane more susceptible to weathering and erosion than the rock around it. Thus, the location of large features of the landscape, such as valleys and cliffs, and may be influenced by the position of master joints.
6. What are the general differences between mechanical weathering and chemical weathering? Mechanical Weathering- The physical disintegration of rock material without any changes in its chemical composition; also called physical weathering. Chemical Weathering- The chemical decomposition of rock by alteration of rock-forming minerals.
7. Explain the mechanism of frost wedging.
Fragmentation of rock due to expansion of water that freezes into ice within rock openings. When water in a crack freezes, the ice expansion exerts a force that can deepen and widen the cracks, especially if the process is repeated many times.
8. Explain the process of salt wedging.
Rock disintegration caused by the crystallization of salts from evaporating water. When the water evaporates, as it commonly does, the salts are left behind as tiny crystals. With time, the crystal grow, prying apart the rock grain by grain, much in fashion, previously described for freezing water, although less intensely.
9. Explain the weathering process of exfoliation (“unloading”) that is responsible for features such as exfoliation domes. Exfoliation- Weathering process in which curved layers peel off bedrock in sheets. This process commonly occurs in granite and related intrusive rocks after overlying rock...
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