When a watercourse or small river meanders down a sloping gradient, it will eventually carve out a v-shaped pathway. Due to not having any clear course, the river will often wander back and forth in a zig-zag pattern. The bluffs that are made prominent by the watercourse as its path deepens often appear in a formation not unlike the teeth of a zipper. These ridges are then called interlocking spurs.
Truncated spurs are formed from interlocking spurs. When a glacier moves down the previous river’s pathway, it is unable to flow around the ridges like flowing water could; so it shears the tips off and leaves behind a wide, straight valley with extremely steep sides. Truncated means cut off or terminated, and that is what those interlocking spurs have become.
The spurs appear blunt and triangular in cross-section, and the grooves between them can be sometimes termed as hanging valleys, named so because of the sudden drop at their end. Watercourses flowing down these hanging valleys find this out when they form waterfalls, which then continue their downwards path that leads eventually out to sea.
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