Question

What is hanging valley?

Answer 1

A major glacier is joined by many small glaciers. The valleys of these small glacires lies above the valley of main glacier and are called hanging valleys A valley carved out by a small tributary glacier that joins with a valley carved out by a much larger glacier. The degree to which glaciers can erode down into the landscape is dictated by their size: the larger the glacier, the deeper the valley it can erode. Thus small glaciers can erode only shallow valleys while large glaciers can erode much deeper valleys. A hanging valley is a shallow valley carved by a small glacier and thus the elevation of the valley floor is "hanging" high above the elevation of the valley floor carved out by the larger glacier.

The hanging valley in the top right photo in Glacier National Park contains a waterfall called Bird Woman Falls. A small glacier flowed out of this valley and joined a larger valley glacier that flowed where Logan Creek is located today. Since this glacier was small compared to the glacier that carved out the valley occupied by Logan Creek, it was unable to erode down into the landscape very far and a hanging valley is what you see today. You are looking toward the south-southeast in this photo. On the map, north is toward the top. The photo was taken from the camera location on the map. The floor of the hanging valley is relatively flat and thus the contour lines on the topographic map are more widely spaced than those contours representing the sides of the valley. The close spacing of the contour lines at the edge of the hanging valley indicates a steep drop-off, which is where the waterfall is located. The hanging valley in the bottom right photo is located along Milford Sound on the South Island of New Zealand. The water in the foreground is part of Milford Sound, a huge U-shaped valley now flooded with sea water. Because the size of a glacier determines the depth of the valley the glacier can erode, glaciers that flow into the ocean can carve out valleys with bottoms located below sea level. Glacial troughs filled with sea water are called fjords. The glacier that carved out the hanging valley was smaller than the glacier that carved out Milford Sound and as a result its valley bottom is at a higher elevation than the bottom of Milford Sound. Like the hanging valley in Glacier National Park shown above, this hanging valley in New Zealand also has a waterfall where it joins the main valley.