PHYTOGENIC PSEUDOKARST AND CONDITIONS OF ITS FORMATION

Lavrusevich A.A.^*1, Tsutsupa T.A.^**2,
Saldin V.A.^***3, Lavrusevich I.A.^****1

 ¹ National Research Moscow State University of Civil Engineering, Moscow
² Orel State University, Orel
³ Federal Research Centre, Komi Science Centre, the Ural Branch, Russian Academy of Sciences, Syktyvkar

*E-mail: lavrusevich@yandex.ru
**E-mail: tsutsupa@mail.ru
***E-mail: victorsaldin@yandex.ru
****E-mail: 4914907@gmail.com

The article provides data on the underground (subsurface) erosion – a complex geological process, pseudokarst being one of its manifestations. The dynamic development of pseudokarst is most often related to technogenesis, especially in the past decades, what puts that hazardous geological process in one row with other geohazards, i.e., mudflows, avalanches, karst etc. The pseudokarst typification, which was originally suggested at the international congress in Switzerland, is represented. The terraces of the Shchugor River (the right-bank tributary of the Pechora river) provide an example of the newly set type of pseudokarst, related to abiotic and biotic (vegetation) factors. It is shown that in the natural environment of the North and Nether-Polar Urals (the territory that belongs to the boreal-continental region of Europe) a very unusual type of pseudokarst develops in the slope part of the terraces, which exerts a negative effect on the stability of the near-edge part of the terraces. The development of extended small-diameter cavities under the surface of the root layer in the near-edge part of river terraces leads to the disintegration of the massif and general disturbance of stability. Root systems of woody and perennial herbaceous plants are evenly distributed in the root layer, especially in its upper part, that form vast intertwinements that help to retain the soil. For example, the spruce tap root stops its elongation in 2–3 years and transforms into the thickening, from which the horizontal roots extend. This is due to the phylogenetic development of spruce trees in mountainous conditions, on immature soils, since here horizontal roots are crucial for the life sustaining of trees. The fibrous root system of perennial grasses is also widely developed in the root layer that slows down the speed of water streams during rainfalls and snow melting, dividing flows into smaller streamlets, that helps to protect the soil from washing out. Such root layer, up to several tens of centimeters thick, is strong enough to hold the overlap of the erosional cavities formed below. Often, a smooth subsidence of the surface is observed over the cavities. Any movement along the edge of the terrace ledge by car or on foot, over the formed pseudokarst cavities, can lead to a sudden collapse. The specific mechanism and the rate of development of “phytogenic” pseudokarst with the lack of understanding of its formation conditions, can lead to the development of a landslide process or contribute to the landslide destruction of the terrace ledge due to the successive cyclic retreat of the terrace edge in the zone of pseudokarst development.

Key words: underground (subsurface) erosion, piping, pseudokarst, root layer, phytogenic pseudokarst, erosion channel, northern and subpolar urals, shchugor river

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