Why do some rivers have waterfalls and others don't?

Waterfalls need specific geological conditions to form, not just flowing water. They typically require hard rock sitting on top of softer rock (which erodes at different rates), faults that create sudden drops, or hanging valleys left behind by glaciers.

What causes a hanging valley waterfall?

Hanging valley waterfalls form when glaciers carve valleys at different depths. The larger glacier in the main valley cuts much deeper than smaller glaciers in side valleys, so when the ice melts, tributary streams have to plunge down suddenly to meet the main river below.

What makes hard rock and soft rock create waterfalls?

When hard rock (like basalt) sits on top of softer rock (like sandstone), the softer rock underneath erodes much faster. This creates an overhang that eventually becomes unsupported, forcing the water to plunge over it rather than flow smoothly.

How the Hills Got Here

Why Waterfalls Form in Certain Places

Waterfalls commonly form where hard rock overlies softer rock, where faults create a step, or where a glacial hanging valley meets a deeper main valley. Erosion then changes the fall and can move it gradually upstream.

13 September 20266 min read