How do glaciers carve fjords along mountainous coasts?

Fjords are formed through the intense erosive power of glaciers that flow through mountainous coastal valleys. As these massive ice bodies move toward the sea, they reshape the landscape by removing loose debris and aggressively eroding the underlying bedrock along the valley floor and lower sidewalls.1234

This process transforms V-shaped river valleys into characteristic U-shaped valleys with steep, often vertical walls. The glaciers are capable of carving these valleys to great depths—sometimes thousands of feet below sea level—because their immense weight and thickness allow them to erode the bedrock before they begin to float in the ocean.142

The erosive capacity is greatest in the middle and upper reaches of the valley, where the ice moves most vigorously. Once the glaciers eventually melt, the sea inundates the deep, carved troughs, creating the long, narrow inlets known as fjords. While some debate exists regarding the extent to which tectonic activity may influence their relief, the deep, U-shaped morphology is fundamentally a product of glacial scouring.152