An interlocking spur, also known as an overlapping spur, is one of any number of projecting
ridge
A ridge is a long, narrow, elevated geomorphologic landform, structural feature, or a combination of both separated from the surrounding terrain by steep sides. The sides of a ridge slope away from a narrow top, the crest or ridgecrest, wi ...
s that extend alternately from the opposite sides of the wall of a young,
V-shaped valley down which a river with a winding course flows. Each of these spurs extends laterally into a concave bend of the river such that when viewed either upstream or from overhead, the projecting ridges, which are called ''spurs'', appear to "interlock" or "overlap" in a staggered formation like the teeth of a zipper.
[Jackson, JA, J Mehl and K Neuendorf (2005) ''Glossary of Geology.'' American Geological Institute, Alexandria, Virginia. 800 pp. ]
While similar in general appearance, the mechanism behind the formation of interlocking spurs is different from that behind
meander
A meander is one of a series of regular sinuous curves in the Channel (geography), channel of a river or other watercourse. It is produced as a watercourse erosion, erodes the sediments of an outer, concave bank (cut bank, cut bank or river cl ...
s, which arise out of a combination of lateral erosion and deposition. Interlocking spurs are formed as either a river or stream cuts its valley into local
bedrock
In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet.
Definition
Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...
. As it entrenches its valley, it preferentially follows and erodes zones of weaknesses within the bedrock that typically consist of intersecting sets of
joints
A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
. This process creates a zig-zagging
fluvial
A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...
valley that "interlock" or "overlap" in a staggered manner.
If the river valley is subsequently subject to glaciation,
glacial
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
erosion widens the V-shaped valley and removes the ends of the interlock spurs projecting into the valley. As a result, the ridges are truncated to form ''
truncated spurs''.
[Thornbury, W. D. (1954) ''Principles of Geomorphology.'' John Wiley and Sons, Inc. New York. 618 pp. ]
References
External links
Animation of development
Geomorphology
Fluvial landforms
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