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Why can small streams form high waterfalls along fjord walls?

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Snow-capped, rugged Atlas Mountains encircle a green valley with scattered trees, terraced fields, and a few small buildings in Morocco. — valley The rugged Atlas Mountains surround a valley in Morocco.

Small streams form high waterfalls along fjord walls primarily due to the creation of hanging valleys during the process of glaciation.123

When a major glacier carves a deep, wide U-shaped valley, it erodes the main trunk valley much more rapidly and deeply than the smaller tributary glaciers that feed into it. Because the main glacier has greater mass and erosive power, the floors of the tributary valleys are left at a significantly higher elevation than the floor of the main valley once the ice melts.124

After deglaciation, these elevated tributary valleys are known as hanging valleys. When streams flow through these hanging valleys to join the main drainage system, they must plunge over the steep, vertical walls of the fjord to reach the water below, resulting in the formation of high waterfalls. This phenomenon is a characteristic feature of landscapes shaped by glacial erosion.1253