Fluvio-thermal erosion

Last updated May 29, 2020

In geomorphology fluvio-thermal erosion is the combined mechanical and thermal erosion of an unfrozen river or stream against ice-rich soils and sediments. The erosional process includes the thawing of ice sediments by a strong water flow and once the surface is unfrozen, mechanical erosion occurs only if hydraulic forces are powerful enough to incise the riverbank material.^[1] This kind of erosion sometimes causes the banks to collapse into the river, and when this occurs collapses are commonly controlled by ice wedges.^[2] Rivers where this process has been observed include the Lena, the Colville River delta, and the Yukon River.^[2]

The Yakutia region in Central Siberia, where the Lena River is located, is an exceptional point of interest to study this type of erosion based on its record low temperatures and extreme thickness of permafrost. During the winter when water level is low, a thick sheet of ice forms on top of the Lena River, that is sometimes as much as 2 m thick. Seasonal floods caused by rapid snowmelt and irregular storms then break the ice apart in the summer, exposing the banks of the river to the power of erosion. There are two stages to this process: the first is the breakup of the ice and the second is the flooding. Over the course of just a few days in May or June, water discharge can increase by 10x its velocity. The force of the water causes the ice sitting on top of the river to break apart, and these broken pieces are thrust up onto the riverbanks, sometimes forming an ice barrier that as high as 10m tall that will protect the banks from erosion for a short time.^[3] However, as the flood continues, the warmth and mechanical energy from the water melts the ice barrier, giving way for the fluvio-thermal erosion of the frozen riverbanks. For the Lena, the banks are observed to retreat approximately 40 m per year.

Based on lab models carried out in a cold room, high water temperature, ice temperature, and discharge are shown to be the main contributors of thermal erosion, whereas high ice content in the soil is shown to slow down the thermal erosion process. Melting of the ice within a porous material reduces the strength of the material, rendering it easily breakable and removable.^[4] During the melting period of a periglacial river in the summer, due to a relatively high water discharge, the unfrozen sediments are weathered away. In conclusion, water discharge in permanent contact with permafrost banks creates a combination of thermal and mechanical erosion.

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Soil erosion is the displacement of the upper layer of soil, it is one form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolean) erosion, zoogenic erosion and anthropogenic erosion. Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing a serious loss of topsoil. The loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality and damaged drainage networks.Soil erosion could also cause sinkholes.

Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near the Earth's surface. Geomorphologists seek to understand why landscapes look the way they do, to understand landform history and dynamics and to predict changes through a combination of field observations, physical experiments and numerical modeling. Geomorphologists work within disciplines such as physical geography, geology, geodesy, engineering geology, archaeology, climatology and geotechnical engineering. This broad base of interests contributes to many research styles and interests within the field.

Permafrost is ground that continuously remains frozen for two or more years, located on land or under the ocean. Permafrost does not have to be the first layer that is on the ground. It can be an inch to over miles deep into the Earth’s surface. Some of the most common permafrost locations are located in the Northern Hemisphere. 85% of Alaska, Greenland, Canada, and Siberia is sitting on top of a layer of permafrost, that is almost a quarter of the Northern Hemisphere. It can also be located in the Southern Hemisphere, just on mountain tops. Permafrost frequently occurs in ground ice, but it also can be presented in non-porous bedrock. Permafrost is formed from ice holding all different sorts of soil, sand, and rock combination together.

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 fluvioglacial is used.

Kobuk River watercourse in the United States of America

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Thermokarst is a land surface characterised by very irregular surfaces of marshy hollows and small hummocks formed as ice-rich permafrost thaws, that occurs in Arctic areas, and on a smaller scale in mountainous areas such as the Himalayas and the Swiss Alps. These pitted surfaces resemble those formed by solution in some karst areas of limestone, which is how they came to have karst attached to their name without the presence of any limestone. Small domes that form on the surface due to frost heaving with the onset of winter are only temporary features. They then collapse with the arrival of next summer's thaw and leave a small surface depression. Some ice lenses grow and form larger surface hummocks, which last many years and sometimes become covered with grasses and sedges, until they begin to thaw. These domed surfaces eventually collapse either annually or after longer periods and form depressions which contribute to uneven surfaces. These are included within the general label of thermokarst.

Pingos are intrapermafrost ice-cored hills, ranging in height from 3m to 70m and 30m to 1000m in diameter . They are typically conical in shape and grow and persist only in permafrost environments, such as the Arctic and subarctic. A pingo is a periglacial landform, which is defined as a non-glacial landform or process linked to colder climates. It is estimated that there are more than 11 000 pingos on Earth. The Tuktoyaktuk peninsula area has the greatest concentration of pingos in the world with a total of 1350 pingos. There is currently remarkably limited data on pingos.

In geology, a terrace is a step-like landform. A terrace consists of a flat or gently sloping geomorphic surface, called a tread, that is typically bounded on one side by a steeper ascending slope, which is called a "riser" or "scarp". The tread and the steeper descending slope together constitute the terrace. Terraces can also consist of a tread bounded on all sides by a descending riser or scarp. A narrow terrace is often called a bench.

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Aufeis,, is a sheet-like mass of layered ice that forms from successive flows of ground water during freezing temperatures. This form of ice is also called overflow, icings, or the Russian term, naled. The term was first used in 1859 by A. T. von Middendorff following his observations of the phenomenon in northern Siberia.

Palsa A low, often oval, frost heave occurring in polar and subpolar climates

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A frost boil, also known as mud boils, a stony earth circles, frost scars, or mud circles, are small circular mounds of fresh soil material formed by frost action and cryoturbation. They are found typically found in periglacial or alpine environments where permafrost is present, and may damage roads and other man-made structures. They are typically 1 to 3 metres in diameter.

Frost weathering Mechanical weathering processes induced by the freezing of water into ice

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Periglaciation describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and other structures. "Periglacial" suggests an environment located on the margin of past glaciers. However, freeze and thaw cycles influence landscapes outside areas of past glaciation. Therefore, periglacial environments are anywhere that freezing and thawing modify the landscape in a significant manner.

In geography azonal is an adjective that refers to processes or things that are not restricted to any climate zone. It can be used to describe soils, landforms, geomorphic processes or vegetation. In some climatic environments azonal geomorphologic processes may take distinct characteristics. For example, river activity is common across the globe, but in periglacial environments it causes spring floods from snowmelt, freezing and break-up cycles, and sometimes fluvio-thermal erosion.

Syngenetic permafrost growth is a mode of the growth of permafrost whereby additional material is deposited to a permafrost site during freezing conditions, causing the permafrost layer to build upwards. It is cited as an efficient mode of permafrost growth, compared with heterogenetic permafrost growth, which occurs when freezing temperatures penetrate into previously unfrozen ground of uniform composition. Lunardini gives the basic formulas for permafrost generation under both modes.

References

Costard, Francois, E. Gautier, A. Fedorov, P. Konstantinov and L. Dupeyrat. (2014). An Assessment of the Erosion Potential of the Fluvial Thermal Process during Ice Breakups of the Lena River (Siberia). John Wiley & Sons Ltd. p. 162-171.
Costard, F., E. Gautier, D. Brunstein, J. Hammadi, A. Fedorov, D. Yang, and L. Dupeyat. (2007). Impact of the global warming on the flvial thermal erosion over the Lena River in Central Siberia. The American Geophysical Union.
Costard, F., L. Dupeyrat, E. Gautier and E. Carey-Gailhardis. (2003). Fluvial Thermal Erosion Investigations Along a Rapidly Eroding River Bank: Application to the Lena River (Central Siberia). Wiley InterScience.
Dupeyrat, L., F. Costard, R. Randriamazaoro, E, Gailhardis, E. Gautier, A. Fedorov .(2011). Effects of Ice Content on the Thermal Erosion of Permafrost: Implications of Coastal and Fluvial Erosion. Wiley Online Library.
Randriamazaoro, R., L. Dupeyat, F. Costard and E. Carey Gailhardis. (2007). Fluvial Thermal Erosion: heat balance integral method. Wiley InterScience.

Notes

↑ Dupeyrat, L (2011). "Effects of Ice Content on the Thermal Erosion of Permafrost: Implications for Coastal and Fluvial Erosion". Permafrost and Periglacial Processes. 22 (2): 179–187. doi:10.1002/ppp.722.
1 2 French, Hugh M. (2007). The Periglacial Environment (3rd ed.). John Wiley & Sons Ltd. p. 260. ISBN 978-0-470-86588-0.
↑ Costard, Francois (2014). "An Assessment of the Erosion Potential of the Fluvial Thermal Process during Ice Breakups of the Lena River (Siberia)". Permafrost and Periglacial Processes. 25 (3): 162–171. doi:10.1002/ppp.1812.
↑ Randriamazaoro, R (2007). "Fluvial thermal erosion: heat balance integral method". Earth Surface Processes and Landforms. 32 (12): 1828–1840. Bibcode:2007ESPL...32.1828R. doi:10.1002/esp.1489.

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[1] Dupeyrat, L (2011). "Effects of Ice Content on the Thermal Erosion of Permafrost: Implications for Coastal and Fluvial Erosion". Permafrost and Periglacial Processes. 22 (2): 179–187. doi:10.1002/ppp.722.

[French2007-2] 1 2 French, Hugh M. (2007). The Periglacial Environment (3rd ed.). John Wiley & Sons Ltd. p. 260. ISBN 978-0-470-86588-0.

[3] Costard, Francois (2014). "An Assessment of the Erosion Potential of the Fluvial Thermal Process during Ice Breakups of the Lena River (Siberia)". Permafrost and Periglacial Processes. 25 (3): 162–171. doi:10.1002/ppp.1812.

[4] Randriamazaoro, R (2007). "Fluvial thermal erosion: heat balance integral method". Earth Surface Processes and Landforms. 32 (12): 1828–1840. Bibcode:2007ESPL...32.1828R. doi:10.1002/esp.1489.