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Abrasion (geology)

Abrasion (geology)
Abrasion is a process of erosion which occurs when material
being transported wears away at a surface over time. It is the
process of friction caused by scuffing, scratching, wearing
down, marring, and rubbing away of materials. The intensity of
abrasion depends on the hardness, concentration, velocity and
mass of the moving particles. Abrasion generally occurs four
ways.[1][2] Glaciation slowly grinds rocks picked up by ice
against rock surfaces.[3] Solid objects transported in river
channels make abrasive surface contact with the bed and walls.
Objects transported in waves breaking on coastlines cause
abrasion. And, finally, abrasion can be caused by wind
transporting sand or small stones against surface rocks.
Glacially abraded rocks in western
Norway near Jostedalsbreen
Abrasion, under its strictest definition, is commonly confused with attrition. Both abrasion and
attrition refer to the wearing down of an object. Abrasion occurs as a result of two surfaces rubbing
against each other resulting in the wearing down of one or both of the surfaces. However, attrition
refers to the breaking off of particles (erosion) which occurs as a result of objects hitting against
each other. Abrasion leads to surface-level destruction over time, whereas attrition results in more
change at a faster rate. Today, the geomorphology community uses the term "abrasion" in a looser
way, often interchangeably with the term "wear".[4]
In channel transport
In coastal erosion
From glaciation
From wind
In channel transport
Abrasion in a stream or river channel occurs when the sediment carried by a river scours the bed
and banks, contributing significantly to erosion. In addition to chemical weathering and the
physical weathering of hydraulic action, freeze-thaw cycles (see frost weathering), and more, there
is a suite of processes which have long been considered to contribute significantly to bedrock
channel erosion include plucking, abrasion (due to both bedload and suspended load), solution,
and cavitation.[5][6]
Bedload transport consists of mostly larger clasts, which cannot be picked up by the velocity of the
streamflow, rolling, sliding, and/or saltating (bouncing) downstream along the bed. Suspended
load typically refers to smaller particles, such as silt, clay, and finer grain sands uplifted by
processes of sediment transport. Grains of various sizes and composition are transported
differently in terms of the threshold flow velocities required to dislodge and deposit them, as is
modeled in the Hjulström curve. These grains polish and scour the bedrock and banks when they
make abrasive contact.
In coastal erosion
Coastal abrasion occurs as breaking ocean waves containing a
sand and larger fragments erode the shoreline or headland.
The hydraulic action of waves contributes heavily. This
removes material, resulting in undercutting and possible
collapse of unsupported overhanging cliffs. This erosion can
threaten structure or infrastructure on coastlines, and the
impact will very likely increase as global warming increases sea
level rise.[7] Seawalls are sometimes built-in defense, but in
many locations, conventional coastal engineering solutions
such as sea walls are increasingly challenged and their
maintenance may become unsustainable due to changes in
climate conditions, sea-level rise, land subsidence, and
sediment supply.[8]
Abrasion platform in the Parque
Natural del Estrecho, at the Strait of
Gibraltar coast in Andalusia, Spain
Abrasion platforms are shore platforms where wave action abrasion is a prominent process. If it is
currently being fashioned, it will be exposed only at low tide, but there is a possibility that the
wave-cut platform will be hidden sporadically by a mantle of beach shingle (the abrading agent). If
the platform is permanently exposed above the high-water mark, it is probably a raised beach
platform (aka, marine terrace), which is not considered a product of abrasion but may be undercut
by abrasion as sea level rises.
From glaciation
Glacial abrasion is the surface wear achieved by individual clasts, or rocks of various sizes,
contained within ice or by subglacial sediment as the glacier slides over bedrock (Krabbendam &
Glasser 2011). Abrasion can crush smaller grains or particles and remove grains or multigrain
fragments, but the removal of larger fragments is classified as plucking (or quarrying), the other
major erosion source from glaciers. Plucking creates the debris at the base or sides of the glacier
that causes abrasion. While plucking has generally been thought of as a greater force of
geomorphological change, there is evidence that in softer rocks with wide joint spacing that
abrasion can be just as efficient.[9] A smooth, polished surface is left behind by glacial abrasion,
sometimes with glacial striations, which provide information about the mechanics of abrasion
under temperate glaciers[10]
From wind
Much consideration has been given to the role of wind as an agent of geomorphological change on
Earth and other planets (Greely & Iversen 1987). [[Aeolian processes| processes involve wind
eroding materials, such as exposed rock, and moving particles through the air to contact other
materials and deposit them elsewhere. of these forces are notably similar to models in fluvial
environments. Aeolian processes demonstrate their most notable consequences in arid regions of
sparse and abundant unconsolidated sediments, such as sand. There is now evidence that bedrock
canyons, landforms traditionally thought to evolve only from the fluvial forces of flowing water,
may indeed be extended by the aeolian forces of wind, perhaps even amplifying bedrock canyon
incision rates by an order of magnitude above fluvial abrasion rates.[11] Redistribution of materials
by wind occurs at multiple geographic scales and can have important consequences for regional
ecology and landscape evolution.[12]
1. Westgate, L. G. (1907). Abrasion by Glaciers, Rivers, and Waves. The Journal of Geology,
15(2), 113-120.
2. Monroe, James Stewart, Reed Wicander, & Richard W. Hazlett. (2011) Physical Geology:
Exploring the Earth. Cengage Learning ISBN 9781111795658. pg 465,591
3. Bennett, Matthew M., & Neil F. Glasser. Glacial Geology: Ice Sheets and Landforms. (2011)
Ch. 5 Glacial abrasion. John Wiley & Sons. ISBN 9781119966692
4. Chatanantavet, P., & Parker, G. (2009). Physically based modeling of bedrock incision by
abrasion, plucking, and macroabrasion. Journal of Geophysical Research: Earth Surface,
114(F4). http://onlinelibrary.wiley.com/doi/10.1029/2008JF001044/full
5. Whipple, K. X., Hancock, G. S., & Anderson, R. S. (2000). River incision into bedrock:
Mechanics and relative efficacy of plucking, abrasion, and cavitation. Geological Society of
America Bulletin, 112(3), 490-503.
6. Allan, J. D. & Castillo, M. M. (2007). Stream ecology: the structure and function of running
waters. Springer Science & Business Media. ISBN 978-1-4020-5582-9.
7. Zhang, K., Douglas, B. C., & Leatherman, S. P. (2004). Global warming and coastal erosion.
Climatic Change, 64(1-2), 41.
8. Temmerman, S., Meire, P., Bouma, T. J., Herman, P. M., Ysebaert, T., & De Vriend, H. J.
(2013). Ecosystem-based coastal defense in the face of global change. Nature, 504(7478), 79.
9. Krabbendam, M., & Glasser, N. F. (2011). Glacial erosion and bedrock properties in NW
Scotland: abrasion and plucking, hardness and joint spacing. Geomorphology, 130(3-4), 374383.
10. Iverson, N. R. (1991). Morphology of glacial striae: implications for abrasion of glacier beds and
fault surfaces. Geological Society of America Bulletin, 103(10), 1308-1316.
11. Perkins, J. P., Finnegan, N. J., & De Silva, S. L. (2015). Amplification of bedrock canyon
incision by the wind. Nature Geoscience, 8(4), 305.
12. Okin, G. S., D. A. Gillette, and J. E. Herrick. (2006). "Multi-scale controls on and consequences
of aeolian processes in landscape change in arid and semi-arid environments." Journal of Arid
Environments 65.2: 253-275.
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