A valley that has been glaciated by a smaller side glacier and is left standing higher than the main u-shaped valley is a hanging valley.
A hanging valley is a valley that is glaciated out by a small tributary glacier that connects with a valley carved out by a much larger glacier. If waterfalls is present, the hanging valley joins the main U-shaped valley. A hanging valley can be formed when the rate of erosion of the lower valley is high. It can also be formed when there is high flow of water in the lower valley or soft rock layers that wears away quickly.