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An Overview of Geomorphology

Geomorphology and Geomorphologic Processes

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Glacier

A glacier is a powerful geomorphologic process.

Getty Images/Tom Brakefield
Geomorphology is defined as the science of landforms with an emphasis on their origin, evolution, form, and distribution across the physical landscape. An understanding of geomorphology and its processes is therefore essential to the understanding of physical geography.

History of Geomorphology

Although the study of geomorphology has been around since ancient times, the first official geomorphologic model was proposed between 1884 and 1899 by the American geographer, William Morris Davis. His geomorphic cycle model was inspired by theories of uniformitarianism and attempted to theorize the development of various landform features.

Davis's geomorphic cycle model says that a landscape undergoes a preliminary uplift that is paired with erosion (the removal or wearing down) of materials in that uplifted landscape. Within the same landscape, precipitation causes streams to flow more rapidly. As they grow their power then cuts into the ground's surface both at the start of the stream and lower down the stream. This creates the stream channels present in many landscapes.

This model also says that the slope angle of the land is gradually reduced and the ridges and divides present in certain landscapes become rounded over time because of erosion. The cause of this erosion is not however limited to water as in the stream example. Finally, according to Davis's model, over time such erosion occurs in cycles and a landscape eventually morphs into an old erosional surface.

Davis's theory was important in launching the field of geomorphology and was innovative at its time as it was a new attempt to explain physical landform features. Today however, it is not usually used as a model because the processes he described are not so systematic in the real world and it failed to take into account the processes being observed in later geomorphic studies.

Since Davis's model, several alternative attempts have been made to explain landform processes. Walther Penck, an Austrian geographer, developed a model in the 1920s for example, that looked at ratios of uplift and erosion. It did not take hold though because it could not explain all landform features.

Geomorphologic Processes

Today, the study of geomorphology is broken down into the study of various geomorphologic processes. Most of these processes are considered to be interconnected and are easily observed and measured with modern technology. In addition, the individual processes are considered to be either erosional, depositional, or both. An erosional process involves the wearing down of the earth’s surface by wind, water, and/or ice. A depositional process is the laying down of material that has been eroded by wind, water, and/or ice.

The geomorphologic processes are as follows:

Fluvial

Fluvial geomorphologic processes are those related to rivers and streams. The flowing water found here is important in shaping the landscape in two ways. First, the power of the water moving across a landscape cuts and erodes its channel. As it does this, the river shapes its landscape by growing in size, meandering across the landscape, and sometimes merging with other rivers forming a network of braided rivers. The paths rivers take depend on the topology of the area and the underlying geology or rock structure found where it's moving.

In addition, as the river carves its landscape it carries the sediment it erodes as it flows. This gives it more power to erode as there is more friction in the moving water, but it also deposits this material when it floods or flows out of mountains onto an open plain in the case of an alluvial fan (image).

Mass Movement

The mass movement process, also sometimes called mass wasting, occurs when soil and rock moves down a slope under the force of gravity. The movement of the material is called creeping, slides, flows, topples, and falls. Each of these is dependent on the speed of movement and composition of the material moving. This process is both erosional and depositional.

Glacial

Glaciers are one of the most significant agents of landscape change simply because of their sheer size and power as they move across an area. They are erosional forces because their ice carves the ground beneath them and on the sides in the case of a valley glacier which results in a U-shaped valley. Glaciers are also depositional because their movement pushes rocks and other debris into new areas. The sediment created by the grinding down of rocks by glaciers is called glacial rock flour. As glaciers melt, they also drop their debris creating features like eskers and moraines.

Weathering

Weathering is an erosional process that involves the chemical break down of rock (such as limestone) and the mechanical wearing down of rock by a plant’s roots growing and pushing through it, ice expanding in its cracks, and abrasion from sediment pushed by wind and water. Weathering can for example result in rock falls and eroded rock like those found in Arches National Park, Utah.

Geomorphology and Geography

One of the most popular divisions of geography is physical geography. By studying geomorphology and its processes, one can gain significant insight into the formation of the various structures found in landscapes worldwide, which can then be used as a background for studying the many aspects of physical geography.

Note: For great photo examples of geomorphologic processes see Professor Lisa Wells' site, Images Illustrating Principles of Geomorphology.

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