Landform - Rivers, Glaciers, Wind, Chemical Dissolution And Precipitation, Differential Weathering And Erosion, Volcanism - Erosion and deposition, Tectonic landforms, Joint sets
rock earth surface continents
A landform is a natural sculpture of the surface of the earth. Most landforms are produced by the actions of weathering and erosion, carving away material from higher elevations and depositing it down lower. Different kinds of rock erode at a variety of rates under particular climatic conditions. As softer rock is worn away the more resistant rock is exposed, producing another series of landforms. Other landforms develop from volcanic activity or movements along faults during earthquakes. Study of landforms reveals much about the deformation, stresses, and strains which have affected the rocks to date at Earth's surface.
Nature's sculpting tools are the agents of weathering, mass wasting, and erosion. Weathering breaks down bedrock into transportable fragments, mass wasting moves the fragments down hill, and erosion transports them in a number of different ways. Each process can produce characteristic landforms.
If nothing countered weathering and erosion, the continents would be reduced to sea level in a few million years. Tectonic processes, driven by the gradual movements of giant global plates, raise the elevations of parts of the continents, producing their own landforms.
Sometimes sets of fractures develop where the surface of the earth is stretched. Such fractures have no displacement along them, and are called joints. Weathering, particularly in arid regions, may exploit these joints, leaving a series of vertical slabs of rock. Continued weathering of these slabs can result in the formation of arches, such as those at Arches National Monument, in Utah.
Additional Topics
The ability of water to move sediment depends on its velocity, which is related to the slope of its bed. When it is moving rapidly it can transport a great deal, but if it slows down it deposits its load. High in the mountains the gradient is steep and erosion dominates. Rivers actively cut downward, and mass wasting adjusts the walls to a "V" shape. These valleys intersect in a bran…
A glacier is a flowing mass of solid ice. It erodes the sides of its valley, not just the bottom, resulting in distinctive "U" shaped valleys. The rate at which it erodes is proportional to its depth, because a thicker pile of ice bears down harder on the rocks below. When a glacial tributary joins a larger glacier, the tops of both will usually flow to be at nearly the same elevatio…
Although erosion and deposition are most easily observed where solid sediment is being moved about, invisible chemical reactions also produce landforms. As water moves through the soil it becomes acidic, in part because of the addition of carbon dioxide produced by the decay of organic matter. This weak acid is able to dissolve some kinds of rock, particularly limestone, giving us spectacular unde…
As erosion progresses, by whatever means, some rock units will be more resistant than others. These will be left exposed at higher elevations, and may protect underlying rock. Depending on the orientation and shape of the resistant unit, and the agents of erosion acting on it, various landforms may develop. Although easily attacked in humid regions, limestone is a resistant rock in arid areas. Its…
Volcanism produces a number of landforms. First, of course, are volcanoes themselves. These may be steep sided cinder cones, gently sloping shield volcanoes constructed of lava flows, or a combination of the two, called composite volcanoes, or strato-volcanoes. Cinders and ash fall out of the air and accumulate in steep-sided piles, but these are easily washed away by agents of erosion so they are…
As the plates move about, bending and twisting within them produces fractures called faults. Where these reach the surface they can produce scarps—sharp changes in elevation—if movement on the fault had a vertical component. Scarps can be very small, or the size of whole mountain ranges. If a typical mountain range is cut by a fault with large vertical movement, many ridges may be be…
In addition to producing its own distinctive land-forms, deformation of Earth's crust is influential in controlling what landforms result from differential weathering and erosion. During major mountain building episodes huge volumes of rock are compressed, folded into complex three-dimensional forms, and sometimes metamorphosed into different kinds of rocks. Later, when these folded layers …
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