Stories of Erosion

Deforestation Leads to Sedimentation and More: Madagascar Island
Deforestation affects the soil and local climate by reducing the evaporative cooling that takes place from plant life. As a result, temperatures rise. In addition, the loss of vegetation leads to increases in soil erosion and rainfall runoff and drastically affects the biodiversity of the ecological system.

Click here to view a photo taken from the space shuttle on September 7, 1985, showing waters of the Mahajamba Bay on Madagascar Island. This sedimentation, seen flowing to the left into the bay, is a result of extreme erosion due to deforestation.

Source: NASA's Earth Science Enterprise Informational CD-ROM Version

Human-Induced Wind Erosion and More: The Aral Sea
Large bodies of water have a moderating influence on local climate. They are also extremely important to local ecological conditions, helping to determine which life forms can thrive (or survive) in a particular area. The Aral Sea was once one of the Earth's largest bodies of land-locked water. Since 1960, the sea has lost more than 60 percent of its volume. The associated drop in sea level has lowered the surrounding water table. The cause of the depletion of the Aral Sea is the rerouting of two large rivers for the irrigation of cotton fields. The two rivers were major sources of fresh water to the Aral Sea.

Reduced water flow, coupled with evaporation, has had three primary effects: first, the remaining water has become extremely salinized; second, the moderating effect of the Aral Sea on local climate has diminished, resulting in hotter summers, colder winters, and a decreased growing season; third, over 20,000 square kilometers of land that were once submerged now are exposed. Dust storms raise up massive amounts of salt from the exposed sea bed and move it hundreds of kilometers away, depositing on surrounding land and reducing crop production.

If this process continues at the same rate, the Aral Sea will cease to exist by the year 2020. Click here to view two images from NASA's Landsat Multi Spectral Scanner (MSS).

Source: NASA's Earth Science Enterprise Informational CD-ROM Version 3

What Comes Around Goes Around: Cincinnati, OH

Around the completion of this online investigation, a severe thunderstorm blew through my community. Due to a combination of our dog's desire to dig and drought conditions, our yard was ripe for erosion. These pictures show the area where the erosion originated and the sediment that was carried around the house and out to the storm sewer. Perhaps I should call on the Wilmington Middle School students to solve my erosion problem!

John Farmer

Topography

Knowledge of the topography of the Earth's surface is important for many Earth Observation System (EOS) studies. On a global scale, topography affects the circulation of the atmosphere and ocean water. The topography of continents affects the gravity field, the interpretation of which, in turn, provides information on the geology and structure of the land. Locally, the topography must be known in order to predict areas of flooding, the distribution of vegetation types, and the degree of soil erosion to be expected.

The hue and saturation of colors in this image are controlled by the depth or elevation of the land. The colors indicate the depth, from darkest blue the deepest to bright red the highest points.

Source: NASA's Earth Science Enterprise Informational CD-ROM Version 3

Coastal Changes Which Lead to Erosion and More
Shoreline changes have become of paramount concern for coastal engineers and land use planners because a significant portion of the world's population lives within the coastal zone. The continuance of coastal change is virtually assured due to natural forces and human modifications. Moreover, should global warming occur, it will add to this effect by melting land-based ice and causing the near-surface ocean waters to expand thermally, raising sea levels in the future. Sea level rise is one of the most certain consequences of the greenhouse effect, and is an indicator of climate change.

Sea level rise caused by global warming will have pronounced impacts on coastal areas by causing submergence of low-lying areas and loss of wetlands, as well as erosion of beaches. Unfortunately, many of the buildings and facilities humans have built along the coasts are not adequately above existing water levels or located far enough inland to ensure survival and safety of residents during storms. This hazard is becoming increasingly apparent as relative sea levels have risen throughout the twentieth century.

Click here to view and Earth Observation System (EOS) image which highlights coastal change.

Source: NASA's Earth Science Enterprise Informational CD-ROM Version 3

Erosion Helpful to Anthropologists
A recent Smithsonian expedition the early human site of Olorgesailie offers a view into the world of eastern Africa nearly 1 million years ago. It is situated in the East African Rift Valley, roughly 70 km to the southwest of Nairobi (see map). The Rift Valley occupies the central and western portions of Kenya. It is best described as a scar in Earth's surface caused over millions of years by the divergence of two tectonic plates, large portions of our planet's crust that are spreading apart.

Fortunately for these anthropologists, recent erosion has exposed a jumble of stone tools left by our ancestors, buried by the sediments of a local stream channel nearly 900,000 years ago, and then re-exposed to the elements by recent erosion. These areas of erosion allowed them to find the actual layer of burial in a nearby hillside. At that point careful excavation can occur. By careful study of the position of the objects and any evidence of edge rounding, the excavated tools may help answer whether or not they were originally deposited on the spot by early people or carried here through sedimentation by flowing water from some other place the toolmakers lived. Only by doing this painstaking record-keeping can they figure out whether this particular place was visited by the Stone-Age toolmakers many times, only once...or never at all.

Source: The Smithsonian Olorgesailie Prehistoric Site website