An interlocking spur, also known as an overlapping spur, is one of any number of projecting
ridge
A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...
s that extend alternately from the opposite sides of the wall of a young,
V-shaped valley
A valley is an elongated low area often running between Hill, hills or Mountain, mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers ...
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 of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex bank ...
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 (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet.
Definition
Bedrock is the solid rock that underlies looser surface mater ...
. 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
In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...
valley that "interlock" or "overlap" in a staggered manner.
If the river valley is subsequently subject to glaciation,
glacial
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
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
A truncated spur is a spur, which is a ridge that descends towards a valley floor or coastline from a higher elevation, that ends in an inverted-V face and was produced by the erosional truncation of the spur by the action of either streams, wa ...
''.
[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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