Mystery #1Tier 1rivers and erosion

How does a gentle river slice a deep valley through solid rock?

Picture a river winding quietly through the countryside. It looks soft and harmless, water you could splash with one hand. Yet somewhere it has cut a valley so deep you could lose a whole house inside it, straight through solid rock. So how does a gentle river slice a deep valley through solid rock?

A turquoise river running through a narrow rocky gorge between steep forested walls, with pale cobbles piled along its bed — Photo: Pseudopanax · Public domain · via Wikimedia Commons

Your guess

A river looks so gentle and soft. What do you think it could be doing to cut straight through hard rock?

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