Here's why:

* Glaciers: U-shaped valleys are characteristic landforms created by glaciers.

* Erosion: Glaciers are powerful agents of erosion. Their immense weight and slow movement carve out the landscape, eroding both the valley floor and its sides.

* Shape: The unique U-shape is created as the glacier erodes the valley floor, leaving steep, almost vertical sides and a relatively flat bottom.

In contrast to deposition: Deposition occurs when glaciers melt and deposit the eroded material (sediments, rocks, etc.) at the end of the glacier, forming features like moraines.