Desert and Glacial Landscapes

Desert landforms such as plateaus, buttes, and mesas are the product of weathering and erosion but are a function of rock structure. Rocks of different hardnesses and strengths weather at different rates producing some of the fantastic structures seen in deserts. These rock features tend to have angular features due to the lack of rain and therefore, minimal chemical weathering. Though regular rainfall is not a feature of the desert, flash floods carve scarps and gullies out of the landscape. Sand dunes are a very distinctive feature of desert landscapes. These large features possess a structure that can be interpreted to indicate predominant wind direction. Silt and sand deposited by the wind is termed loess.

The depositional environment can be described by the process of abrasion and deflation. This is the process by which sediments carried by the wind, abrade and erode other rock and sediment structures, producing more sediment. The wind is able to carry a certain load, constrained by sediment size and volume, to either be deposited or to continue to erode other landforms.

Glaciers create landforms by erosion and deposition also. As the glacier moves, it can scour out the material beneath it leaving something as large as a lake or as minor as a scrape on a rock face. The material becomes part of the glacier and is eventually dropped somewhere else. Glacial deposits and erosion features give clues as to the direction that the glaciers were moving.

Erosion and deposition in a glacial environment takes the form of either mechanical breakdown (the physical crushing of rocks) and erosion due to water flowing. The deposition can be from material dropping out of the ice pack, deposited by the meltwater or by windblown loess.

Climate change, though it is used in the media currently in terms of global warming, is not a new concept. The Earth's climate has changed many times. Scientists can actually determine when climate changes occurred using things like ice cores from arctic regions, tree rings, and ocean sediments. There are many reasons that climate change can occur. Among these are changes in the orbit of the Earth around the Sun, changes in how intense the Sun is or was, and volcano eruptions that introduce particles and gas into the air. The effect of these climate changes were ice ages or glacial periods and interglacial periods when the Earth warmed.

Greenhouse gasses, such as carbon dioxide, can come from natural sources such as volcanoes and can add to the cooling or warming effect. If the Earth begins to cool due to a change in its orbit, more carbon dioxide gets dissolved into the oceans and makes the Earth even cooler. If the Earth is warming for some reason, not as much carbon dioxide goes into the oceans and that makes it even warmer.

For the past 2000 years, the Earth has been in an interglacial or warming period. There was one relatively small cooling event from about 1500 to 1850 that was called the "Little Ice Age" and caused the Earth to cool by about 2 degrees Fahrenheit. One warming event occurred during medieval times in Europe, though how much it warmed and exactly when it occurred is not certain. Since the beginning of the Industrial Age, the Earth has started to warm at a faster rate. Though the causes are debated, the fact remains that the warming trend matches up with an increase in greenhouse gasses produced by humans.

Over the past century, climate change has resulted in an average temperature increase of 0.6 degrees centigrade. Also, rainfall patterns have changed resulting in more rainfall in some areas and less in others. In addition, sea levels have increased 10 to 20 centimeters. In the future, we can expect further melting and retreat of glaciers, increase in sea level, temperatures will increase, and there will be more extreme weather events. Sea level change will greatly affect coastal regions and there may be more erosion and land subsidence.

Deserts will be affected by climate change as well. Many deserts are semi-arid and the ecosystems that survive in them are dependent upon the little water that they receive from rain or streams. In South America, there are two deserts that are fed by the meltwater from glaciers. When climate change makes the glaciers melt to the point where they can't provide any more meltwater to the deserts, the deserts will become more arid.

In glacial settings, there will be more erosion as the glaciers retreat (mechanical) and produce more meltwater (erosion). The deposition of material that drops out of the glacier would mark the retreat. If a glacier were to completely melt, there would be no more erosion due to the movement of the glacier or the meltwater.

The face of the Earth may change in many ways due to climate change and every environmental and geological setting will be affected.

Reading, H.G., 1996. Sedimentary Environments. Blackwell Publishing.