Why do gorges have steep walls?
Show answer & explanation
Answer: Rivers cut through hard rock
Glaciers carve straight down — Wrong. Glaciers create wide U-shaped valleys. Gorges are narrow, steep-sided valleys carved by rivers cutting through resistant rock.
Earthquakes split the land — Wrong. Earthquakes can create faults but not the V-shaped gorges we see. Gorges form when rivers rapidly cut downward through rock faster than the walls can erode sideways.
Rivers cut through hard rock ✓ — Correct! Gorges are narrow, steep-walled river valleys carved through hard rock. When rivers encounter resistant rock during rapid downcutting (from tectonic uplift or base-level drop), they cut straight down faster than sideways erosion widens the valley. Result: deep, narrow gorge with vertical walls. Columbia River Gorge is a classic example!