If two river basins get similar rain and have similar rock, why might the one closer to active faults erode faster?
Show answer & explanation
Answer: Fault cracks make the same rock easier to remove
Fault cracks make the same rock easier to remove ✓ — Active faults can weaken rock as well as move the landscape. Repeated shaking and slipping leave cracks and damaged zones, so the same stream power can detach and carry away more material. That can make a basin erode faster even when rain and rock type look similar on a map.
More rainwater must be running through it — More runoff would certainly speed erosion, so it is a natural guess. The question, though, holds rainfall similar, which removes that easy explanation. The remaining mechanism is that fault damage changes how easily the bedrock breaks apart under the same water flow.
Its rocks must be a softer kind — Softer rock erodes faster, and geologists do have to control for rock type. But similar rock type does not mean identical strength after tectonic damage. A fault zone can make the same kind of rock more fractured and easier for rivers to remove.
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