Show
Recommended textbook solutionsInvestigating Oceanography3rd EditionKeith A. Sverdrup, Raphael Kudela 547 solutions Environmental Science for AP3rd EditionAndrew Friedland, Rick Relyea 957 solutions Investigating Oceanography2nd EditionKeith A. Sverdrup, Raphael Kudela 538 solutions Living in the Environment17th EditionG. Tyler Miller, Scott E. Spoolman 341 solutions
The rocky surface of the planet is subjected to processes that break down rocks and move materials. This chapter focuses focuses on the weathering and erosion of rocks to form sediments, and the transport and modification of sediments to sites of deposition. Weathering and erosion impact the surface of the land in many way. Much of this relates to the mechanical, chemical, and biological processes breaking down rocks while shaping the landscape, including the formation of soils. Gravity has a large role in moving material downhill in a variety of means called mass wasting. Mass wasting is associated with a variety of serious landslide hazards that are often associated with heavy precipitation. Landslides can take place slowly or rapidly, and intermittently (such as events associated with seasonal storm floods or some that are triggered by earthquakes or human activities). 9.2
Chemical Reactions Involved In WeatheringChemical weathering involves a variety of chemical reactions including hydrolysis, hydration, oxidation, and carbonation.* Hydrolysis is the chemical breakdown of a compound due to reaction with water. * Hydration is the process of combining with water to a molecule. * Oxidation is the process of combining elements with oxygen ions. A mineral that is exposed to air may undergo oxidation. * Carbonation is saturation with carbon dioxide (as soda water). Decaying organic matter releases carbonation and organic acids that enhance the chemical reactivity between rocks and groundwater. All these chemical processes are happening around us. Weathering and erosion are continuous processes in the surface environment, enhanced by the presence of water (the "universal solvent"). In addition, barometric changes in air pressure with passing storm fronts push in or pull out air from the ground. 9.8
What happens to common igneous rocks (granite and basalt) when they weather?Granite is common in mountainous regions in many regions in the western United States. When granite weathers, it separates into components. Mechanical weathering forces split the rock into fragments, and the interactions of water and gases slowly chemically alter some of the minerals into clay. The quartz in granite is most resistant to weathering, and remains virtually unchanged, becoming mostly gravel, sand, and silt. In contrast, the feldspars and micas eventually break down to become clays. Mafic minerals in granite break down into clays and iron-oxide residues (hematite and limonite). Soluble components dissolve and are carried away by groundwater or surface waters, eventually contributing to the salts in seawater.Basalt and most volcanic rocks of mafic and intermediate composition experiences a different fate than granite. Because basalt and these volcanic rocks are dominated by fine grained mafic minerals and feldspars, both of which break down to become clays. Sediments deposited along streams valleys and sediments deposited offshore of volcanic regions are generally dominated by mud (iron mineral residues, silt, and clay) and dissolved fractions contribute salts to seawater. 9.10Effects Of Physical and Chemical Conditions On Weathering
9.11 Factors That Influence Weathering
9.12
Colluvium is a general term applied to loose and incoherent surficial deposits, usually at the base of a slope and brought their chiefly by gravity. Eluvium or eluvial deposits are accumulations of weathered rock fragments and soils that are derived by in-situ weathering (particularly leaching of soluble materials) or weathering plus gravitational movement and accumulation. The process of removal of materials from geological or soil horizons is called eluviation or leaching.Alluvium is a general term for unconsolidated sediments deposited by flowing water, such as on stream channel beds, flood plains, and alluvial fans (discussed in the Deserts chapter). The term, alluvium (or alluvial deposits), applies to stream deposits of recent times and it does not include sub-aqueous deposits, such as in lakes or undersea. On many geologic maps, anything that is an accumulation of sediments on land is called alluvium. However, there are sediment deposits on the surface that are not alluvium (sediments that accumulated not by flowing water alone). 9.15
9.19
Mass WastingMass wasting is a general name for processes by which soil, regolith, and rock move downslope under the force of gravity. Types of mass wasting include landslides, mudflows, debris flows, lahars, topples, rock falls, and avalanches, and creep—each with its own geomorphic characteristics, and taking place over time scales ranging from seconds to years. It does not include surface erosion by running water, however, streams in flood can in some cases carry as much sediment as the water moving downstream. It may be caused by natural erosional processes, by natural disturbances, or by human disturbances. Landslide is a general term covering a wide variety of mass-movement landforms and processes involving the down slope transport of soil and rock under the influence of gravity. Usually the displaced material moves over a relatively confined zone or surface of shear. Landslides
have a great range of morphologies, rates, patterns of movement, and scale. Their occurrence reflects bedrock and soil characteristics and material properties affecting resistance to shear. Landslides are usually preceded, accompanied, and followed by perceptible creep along the surface of sliding and (or) within the slide mass. Slumps, debris flows, rock falls, avalanches, and mudflows are all forms of landslides. Each type has own geomorphic characteristics, and taking place over times scales
ranging from seconds to years. Landslides can be extremely hazardous. Estimates vary, but current thought is that thousands to tens-of-thousands are killed by landslides each year, most often in association with storms in mountainous terrain, and areas of poor land-use planning and building codes. Most deaths occur in Southeast Asia. Landslides associated with large volcanic eruptions can do even greater damage. Damage by "landsliding" causes billions of dollars in damage each year, affecting homes, buildings, roads, bridges, and all kinds of infrastructure. Much of the damage is a result of minor shifts in the soil beneath poorly or improperly-designed foundations. Some regions are more likely to experience landsliding, and it is related to the character of the bedrock and soil, the relief of the land, and the amount a rainfall received in an area. Geologists and engineers classify landslide-prone areas. They use the word susceptibility—defined as the state or fact of being likely or liable to be influenced or harmed by a particular thing. In geology, the term is used as a means of classifying areas that are prone to natural hazards, such as landsliding, liquefaction, flooding, fire, avalanches, etc. Home buyers should really know the risks of landsliding in an area before purchasing! 9.23
Which process moves weathered rock?Weathering is the breaking down or dissolving of rocks and minerals on Earths surface. Once a rock has been broken down, a process called erosion transports the bits of rock and minerals away. Water, acids, salt, plants, animals, and changes in temperature are all agents of weathering and erosion.
What do you call to the movement of the weathered rocks and soil from one place to another?Erosion is the geological process in which earthen materials are worn away and transported by natural forces such as wind or water.
What term refers to transfer of rock and soil downslope under the influence of gravity?A 300-meter long slump that occurred in an area of thawing permafrost (2004). Noatak National Preserve, Alaska. 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.
What is the transport of weathered materials by a moving natural agent called?Erosion is the process by which soil and rock particles are worn away and moved elsewhere by gravity, or by a moving transport agent – wind, water or ice.
|