In
geomorphology fluvio-thermal erosion is the combined mechanical and
thermal erosion of an unfrozen river or stream against ice-rich soils and
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
s. 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
Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...
forces are powerful enough to incise the riverbank material. This kind of erosion sometimes causes the
banks to collapse into the river, and when this occurs collapses are commonly controlled by
ice wedge
An ice wedge is a crack in the ground formed by a narrow or thin piece of ice that measures up to 3–4 meters in length at ground level and extends downwards into the ground up to several meters. During the winter months, the water in the gr ...
s.
Rivers where this process has been observed include the
Lena
Lena or LENA may refer to:
Places
* Léna Department, a department of Houet Province in Burkina Faso
* Lena, Manitoba, an unincorporated community located in Killarney-Turtle Mountain municipality in Manitoba, Canada
* Lena, Norway, a village in ...
, the
Colville River delta, and the
Yukon River
The Yukon River ( Gwich'in: ''Ųųg Han'' or ''Yuk Han'', Yup'ik: ''Kuigpak'', Inupiaq: ''Kuukpak'', Deg Xinag: ''Yeqin'', Hän: ''Tth'echù'' or ''Chuu k'onn'', Southern Tutchone: Chu Nìikwän, russian: Юкон, Yukon) is a major watercourse ...
.
[
The Yakutia region in Central ]Siberia
Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive region, geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a ...
, 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 flood
A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
ing. 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. 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
A porous medium or a porous material is a material containing pores (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid ( liquid or gas). The skeletal material is us ...
reduces the strength of the material, rendering it easily breakable and removable. 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.
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
{{Periglacial environment
Erosion
Soil erosion
Hydrology
Physical geography
Permafrost