What does running water form

Among the terrestrial planets, the Earth is unique in having abundant liquid water. Both Mercury and the Earth's moon are too small to retain water, and Venus, because of its runaway greenhouse effect, is too hot to retain surface water (it is gaseous instead of liquid). Mars has only some frozen water and trace amounts of water vapor in its atmosphere. In marked contrast, 71% of the Earth's surface is covered with water, and a small but important quantity of water vapor is present in its atmosphere. The volume of water on Earth is estimated at 1.36 billion km^3, most of which (97.2%) is in the oceans. About 2% is frozen in glaciers, and the remaining 0.8% constitutes all the water in streams, lakes, swamps, groundwater, and the atmosphere. Thus, only a small portion of the total water on Earth is in streams, but running water is nevertheless the most important erosional agent modifying the Earth's surface. Despite the importance of running water as an agent of erosion, sediment transports, and deposition, its role is limited in some areas. In areas covered by glacial ice, such as Greenland and Antarctica, running water is currently not important. Some parts of deserts are also little affected by running water. Even in most desert regions, though, the effects of running water are manifest, although the channels are dry most of the time In addition to its significance as a geologic agent, running water is important for many other reasons as well. It is a source of fresh (non-saline) water for industry, domestic use, and agriculture, and about 8% of the electricity used in North America is generated by falling water at hydroelectric stations. Streams have been, and continue to be, important avenues of commerce and much of the interior of North America was first explored by following such large streams as the St. Lawrence, Mississippi, and Missouri rivers.