Final answer:
Hanging valleys are glacier-cut valleys that flooded as sea level rose in post-glacial times. These valleys were formed by glaciers that flowed downward between the walls of a valley, resulting in U-shaped valleys.
Step-by-step explanation:
Hanging valleys are glacier-cut valleys that flooded as sea level rose in post-glacial times. These valleys were formed by glaciers that flowed downward between the walls of a valley, resulting in U-shaped valleys. As the glaciers retreated and melted, the main valleys were flooded by rising sea levels, while the smaller hanging valleys remained above the water level.