An Overview of Valley Formation and Development
The definition of a valley as found in the Oxford dictionary is: A low area of land between hills or mountains, typically with a river or stream flowing through it.
As valleys are usually occupied by a river, they can also slope down to an outlet which can be another river, a lake or the ocean. Valleys are also one of the most found landforms on the Earth and they are formed through erosion or the gradual wearing down of the land by wind and water. In river valleys for example, the river acts as an erosional agent by grinding down the rock or soil and creating a valley. The shape of valleys varies but they are typically steep-sided canyons or broad plains, however their form depends on what is eroding it, the slope of the land, the type of rock or soil and the amount of time the land has been eroded.
There are three common types of valleys which include V-shaped valleys, U-shaped valleys and flat floored valleys.
V-Shaped Valleys
A V-shaped valley, sometimes called a river valley, is a narrow valley with steeply sloped sides that appear similar to the letter "V" from a cross-section. A V-shaped valley is formed by vertical erosion caused by rivers. As time goes on the sides are weakened and the erosion of the vertical walls continue. Over time there is mass movement of materials which creates the distinctive V-shape. This material or erosion is then carried away by the river.
An example of a V-shaped valley is the nearby Baakens River Valley that cuts across most of Port Elizabeth.
U-Shaped Valley
A U-shaped valley is a valley with a profile similar to the letter "U." They have been formed by a process of glacial erosion. They are also characterized by having broad, flat valley floors. The glaciers basically alter a V shape into a U, by creating a steep sided, wide valley in the shape of the letter U. They are formed by a valley glacier that moves down the valley because of gravity. Over time as the ice sheet has melted and moved rocks and boulders the U-shaped remains.
The nearby Natures Valley is a small example of a U-shaped Valley formed by glacier movement.
Flat-Floored Valley
The third type of valley is called a flat-floored valley and is the most common type in the world. These valleys, like V-shaped valleys, are formed by streams, but they are no longer in their youthful stage, and are instead considered mature. With these streams, as the slope of a stream's channel becomes smooth, and begins to exit the steep V or U-shaped valley, the valley floor gets wider. Because the stream gradient is moderate or low, the river begins to erode the bank of its channel instead of valley walls. This eventually leads to a meandering stream across a valley floor.
Over time, the stream continues to meander and erode the valley's soil, widening it further. With flood events, the material that is eroded and carried in the stream is deposited which builds up the floodplain and the valley. During this process, the shape of the valley changes from a V or U shaped valley into one with a broad flat valley floor. An example of a flat-floored valley is the Breede River Valley in the Western Cape.
To log this find please answer the following questions and email them to me either via my profile or directly by email bremarjosrut2011@gmail.com
- How many Valleys can you see?
- What kind of Valleys do you see here? Explain your reasoning.
- Estimate the steepness of the valley walls.
- Estimate the depth of the valley.
- It would be great to log a photo of yourself at GZ, however this is only optional.
Reference: http://geography.about.com/od/physicalgeography/a/valleyformation.htm http://geobytesgcse.blogspot.com/2006/11/upper-course-of-river-v-shaped-valleys.html http://en.wikipedia.org/wiki/Valley http://www.coolgeography.co.uk/GCSE/Year%2010/PhysicalWorld/Glacial%20Landforms/glacial_landforms.htm http://www.oxforddictionaries.com/definition/english/valley