Rapids And Waterfalls: The Amazon's source stream, the Maranon, has an altitude of only some 400 feet at the Peruvian border, and the Amazon itself is a mere 130 feet above sea level a thousand miles inland from its mouth.Major irregularities in the gradient, such as waterfalls and rapids, are more common in headwaters than downstream. There are, however, numerous exceptions to this—as, for example, the rapids and falls about 100 miles above the mouth of the Congo. Differential erosion of rocks, movement along faults, and other geologic factors are for small basins having comparable precipitation and rates of loss.
Stream beds in their upper section are often bare rock patchily covered by pebbles. Here the stream has greatest capacity to erode and transport farther downstream all but the largest stones. The valley in the upper course has steep sides and a V-shaped cross-section and most pools, rapids, waterfalls [6] and pot-holes [3] occur here, caused by the stream wearing away softer rock more quickly than hard rock. This results in rapids such as the cataracts of the Nile, and where a river flows from a hard bed of rock to a soft one the latter will be eroded away and a waterfall will be formed as a result.
Gudbrandsdal is narrow and steep-sided along most of its length, and the Lagen River, which rushes through it, is broken by numerous rapids and waterfalls. In a few places where the valley broadens out, relatively dense agricultural settlement is found. Otherwise, habitations are krgely restricted to the valley bottom beside the national highway and main-line railroad that run between Oslo and Trondheim.
|
