Comment: 06:58 - 08:02 (01:04)
Source: Annenberg/CPB Resources - Earth Revealed - 20. Running Water II: Landscape Evolution
Keywords: "Douglas D. Rhodes", "rock type", structure, river, "drainage pattern", stream, geologist, "sedimentary rock", "dendritic pattern", fracture, fault, "intersecting pattern", "trellis pattern", erosion, slope, valley
Our transcription: Ultimately, rock type and rock structure also affect river drainage patterns.
By studying different stream patterns, geologists can infer a great deal about the nature of the underlying rock.
If we have homogenous rocks or flat lying sedimentary rocks, streams typically form what's called a "dendritic pattern," that looks very much like the branching of a tree.
Where the rocks are not homogenous or where there are definite structures in rocks, other patterns occur.
For example, if we have intersecting fractures or faults, streams commonly follow those intersecting patterns.
They make sharp bends at acute or even right angles forming a different kind of stream pattern.
Where we have alternating layers of strong and weak rocks, the streams will usually branch out as a trellis pattern reflecting the weaker valley rocks and the stronger hill forming rocks.
The drainage patterns of streams expand and grow more intricate as the land erodes away.
Geology School Keywords