Truncated spurs are blunt-ended rock ridges which descend from the steep sides of a U-shaped valley or glacial trough. They are often separated by hanging valleys.
Truncated spurs are classic features of upland glacial erosion. Valley glaciers tend to follow a straighter course than river channels. A valley glacier which formed during the last ice age in an upland area will erode the interlocking spurs of the upper course valley, cutting through the projecting ridges.
Good examples are found in the Langdale Valley in the Lake District, and Devil's Pointn the Cairngorms.
Waterfalls are often found in the middle.
Before glaciation, relatively immature rivers display a pattern of interlocking spurs. A valley glacier cannot avoid the interlocking spurs as a river can. As the valley glacier moves, abrasion and plucking erode the protruding tips of the spurs, leaving steep cliff-like truncated spurs. Hanging valleys are found in between truncated spurs as they join the main glacial valley from the side. It is common for waterfalls to form from them, where they fall into the main valley. Such truncated spurs can be found in mountainous regions. The Mer de Glace, in the European Alps, is a valley through which a glacier currently flows. This is a geologically active process where the glacier continues to gradually erode the valley sides.