Along with wind, the flowing water in streams and rivers worldwide is a dominant force in changing the contours of the earth's surface. Constantly moving water carves channels in rock and soil, creating new paths and changing the configuration and shapes of stones. Streams carry tons of sediment and dissolved ions toward the sea, creating new tributaries and networks as they flow around features formed by other processes such as earth movement and volcanic eruptions.
Several stream drainage patterns have been identified, based on physical appearance and associated with the features of the land where they occur. For example, streams in areas rich in seismic faults drain in a recognizable rectangular pattern, while those flowing across the "folded" terrain of areas like the Appalachian Mountains can be described as resembling a garden trellis.
Volcanic activity creates cone-shaped mountains which continue to develop with repeated outflows of lava and changes to the contours caused by eruptions. Around this type of feature, characterized by a centrally elevated point and a sloping drop-off, streams drain in a marked radial pattern, with tributaries draining off the highest point.
Observing stream drainage patterns through aerial photographs and on the ground can provide information about the contours of the earth's surface and the forces which shaped, and continue to shape, them. These patterns may hold important clues to the type of geological formations which lie beneath the stream and its tributaries, and help to identify the seismic, volcanic and erosion processes which created those formations.