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Rio Salado, Argentina Lithograph Answers Why are these small rivers so bright? (Think about what the riverbed might be made of.) These free-flowing rivers have sediments carried along in their channels; in this case, the sediment carried from upstream is of a lighter color than the surrounding area. Also, this photo was taken in October, which is early spring in the southern hemisphere. Early snowmelt in the Andes may be swelling these small rivers, increasing their speed, and creating whitewater. Compare these small rivers to the larger, dammed river. Note that the reservoir is also light-colored. Since the dam causes water to back up behind it, the river flowing into the reservoir slows down, and deposits its sediments there. The river flowing out through the dam appears light-colored for a short ways, where its speed is probably great enough to create whitewater. Farther away from the dam, however, it has resumed a slower pace, and since it no longer carries any sediment, it appears dark. Why are these areas uncultivated? The areas to the edge of the photo are not under cultivation because this area is hilly. In mountainous regions, hillsides are cultivated using terraces, but where flat arable land is still available, the benefits of additional fields do not overcome the difficulties of building terraces. However, the hilly terrain and the change in elevation make possible the creation of a reservoir behind a dam, as can be seen here. Why are they different colors? The agricultural fields will have varying colors, depending on what crop is being grown in them. Each separate field, however, will show very little color variation within itself, since most plots will be planted entirely of the same crop. What is the importance of water in this area? Water is critical to any agricultural area. Most food crops cannot grow well enough to be profitable without some sort of irrigation, and access to a natural water source (such as a river) can provide some insurance against years when rainfall may be inadequate. The shape and size of the fields near the river ("long lot" parcels) show how access to the river is made available to many separate fields. How does the agriculture near the river differ from agriculture away from the river? Near the river, the fields are arranged in long, skinny plots radiating away from the water's edge (with the narrow end along the water). Away from the river, the plots become rectangular and regularly arranged. The riverside parcels are the older, individual farms, while the fields out in the plain are newer, and larger farms, probably irrigated by canals. View the lithograph (pdf). |
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