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Valleys may arise through several different processes. Most commonly, they arise from erosion over long periods by moving water and are known as river valleys. Typically small valleys containing streams feed into larger valleys which in turn feed into larger valleys again, eventually reaching the ocean or perhaps an internal drainage basin.
A river valley civilization is an agricultural nation or civilization situated beside and drawing sustenance from a river. A river gives the inhabitants a reliable source of water for drinking and agriculture. Some other possible benefits for the inhabitants are fishing, fertile soil due to annual flooding, and ease of transportation.
Rôche moutonnée – Rock formation created by the passing of a glacier; Sandur – Plain formed from glacier sediment transported by meltwater; Side valley – Valley with a tributary to a larger river; Summit – Point on a surface with a higher elevation than all immediately adjacent points
This pattern is inherited from the dendritic drainage pattern of the flooded river valley. The drowning of river valleys along a stretch of coast and formation of rias results in an extremely irregular and indented coastline. Often, there are naturally occurring islands, which are summits of partly submerged, pre-existing hill peaks.
The river at left has encountered a formation of erosion-resistant volcanic breccia, causing it to downcut more rapidly on the right, leaving terraces of different elevations. Paired and unpaired terraces: Terraces of the same elevation on opposite sides of either a stream or river are called paired terraces. They occur when it downcuts evenly ...
Dendritic drainage: the Yarlung Tsangpo River, Tibet, seen from space: snow cover has melted in the valley system. In geomorphology, drainage systems, also known as river systems, are the patterns formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of land, whether a particular region is ...
The Snake River Plain can be divided into three sections: western, central, and eastern. The western Snake River Plain is a large tectonic graben or rift valley filled with several kilometers of lacustrine (lake) sediments; the sediments are underlain by rhyolite and basalt, and overlain by basalt.
Long-lived river systems can produce a series of terrace surfaces over the course of their geologic lifetime. When rivers flood, sediment deposits in sheets across the floodplain and build up over time. Later, during a time of river erosion, this sediment is cut into, or incised, by the river and flushed downstream. The previous floodplain is ...