Gorges are a very interesting physical feature of the earth’s surface. They are usually deep openings between higher ground elevations that typically have a river flowing through them. The sides of the gorge are usually steep and the width of a gorge is usually narrow. Gorges are formed due to three different interactions between water and the ground that it flows over.
Uniformitarianism
The first method of gorge formation is through uniformitarianism. This means that the gorge is formed gradually over a very long period of time, usually thousands of years. There are several factors that lead to this formation. Plate tectonics, limestone, and the powerful water flow all play a factor in gradually creating these physical features.
The movement and change of the earth’s surface is known as plate tectonics. The movement can cause the gradual uplifting of ground or the formation of a plateau. Should this occur along a river, then the river may eventually cause the formation of a gorge. The presence of limestone in the rock will also facilitate the creation of a gorge. These types of gorges occur around the world. The limestone is much easier to erode than other rocks as a result of its solubility in water and also the fact that limestone is very sensitive to acids and water is usually slightly acidic.
As a result of the plate tectonics and earth upheaval or plateau formation, water will flow downhill. It might flow gradually downhill or there could be a waterfall. The water may also be seasonal in the case of flooding or even flash flooding. In any case, the water will be fast moving and slowly erode the limestone and other rock that it flows over or the rock behind the waterfall will slightly be eroded. Over time the water will keep removing rock and eventually form a gorge. The erosion will usually occur in the opposite direction that the water flows. So in the most erosion will occur farther down the river and near the end of the plateau.
Caves collapse
The second formation of gorges is basically very similar uniformitariansim but the method is different. Instead of water just slowly eroding the limestone layers away, the water also passed through cracks in the layers and widens the cracks as well as erodes away the limestone layers underneath. This results formation of limestone caves and is very similar to how sinkholes form. As erosion keeps occurring on the surrounding rock and water keeps passing into the caves, the feature will eventually collapse. The collapse will allow the further formation of the gorge. The process could continue with the next layers of limestone and the gorge will deepen as well as propogate.
Catastrophic flooding
The final formation of gorges occurs as the result of a catastrophic flooding. This is not just normal seasonal flooding or from a flash flood but from a gigantic flood. It has been determined that many gorges formed as the result of several extremely large floods that occurred in the past. What makes this creation of gorges different from uniformitariansim is that the gorges were actually formed over a very short period of time. Often the formation occurred thousands of times faster than what normally should have occurred and in the time since then, the gorge has merely been expanded on by uniform erosion.
These gorges have been attributed to the melting of glaciers at the end of the ice age. The water was released from the melting which resulted in a few very large flood events which were far larger than any previous seasonal flooding. The water moved over the surface and collected debris as it went. The fast moving water began carving out gorges into the surface and this was done relatively quickly. Successive floods resulted in short periods of very significant erosion.
