Investigation of past and recent dynamics of Central Yakutian thermokarst landscapes

mathias.ulrich [ at ]


A new project was established to clarify, which parameters are influencing thermokarst dynamics and to assess future landscape evolution and potential hazards associated with thermokarst in Central Yakutia. Two thermokarst key sites were thus investigated in summer 2013. Both sites are located on different Lena River terraces that are geomorphologically classified with regard to differing Yedoma accumulation and degradation. At both sites, the field work included detailed sedimentological, geomorphological, and botanical surveys, as well as bathymetrical measurements. The Yukechi study site located on the higher Abalakh Terrace is characterized by many young thermokarst features surrounding an older alas system. The evolution and age of this alas system still remains uncertain. Several small thermokarst lakes could be explored on the Yedoma remains around the Yukechi alas. Many of these lakes were evidently developed after land use until the 1960’s (e.g. in former agricultural areas). These lakes are no larger than 100m in diameter, about 4-6m deep, and show very strong lake shore expansion in all direction. The Yukechi alas is about 500 m in diameter and about 8-10m deep. During the time of the field trip three alas lakes were measured to be about 2-3 m deep. The bathymetrical profiles reveal the deepest parts are located at the foot of the alas slopes. Different elevated ground levels of the dry alas bottom are likely a sign for spatial differences in the lithology and ground-ice contents and suggests that the current alas system was formed by the coalescence of 3-4 larger (lake-) basins. A talik could be proven below the alas bottom that is about 4.5m deep and possibly mark a residue of recent anomalous years with deep active layers. The second Khara Bulgunakh study site is located on the lower Tyungyulyu Terrace. The investigated alas started to develop about 12 to 10ka BP, is about 1000m in diameter and 5-6m deep, and is part of a large alas system. This basin is a good example for traditionally intensive agricultural use of large alases in Central Yakutia. Large parts of the alas bottom are used for cereal cultivation, hay farming, and pasturing. The lakes inside and around the alas are shallower than the lakes at the Yukechi site. This alas system is furthermore characterized by the existence of several pingos. Pingos are particularly widespread on the Tyungyuluy terrace as sandy deposits below the Yedoma deposits providing the water-bearing layers necessary for pingo genesis. Finally, first insights gained from extensive coring at both thermokarst key sites reveal no clear cryolithological conditions that could be linked to stable lacustrine conditions during alas development, as it would be expected from a classical view on thermokarst evolution. Rather, it appears that lateral expansion by thermo-erosional processes on alas slopes have been the primary processes during alas development in Central Yakutia.

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Conference (Talk)
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4th European Conference on Permafrost, 18 Jun 2014 - 21 Jun 2014, Evora.
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Ulrich, M. , Fedorov, A. N. , Siegert, C. , Schirrmeister, L. , Gogoleva, P. A. , Efremov, P. , Danilov, Y. , Vasiliev, A. and Desyatkin, R. (2014): Investigation of past and recent dynamics of Central Yakutian thermokarst landscapes , 4th European Conference on Permafrost, Evora, 18 June 2014 - 21 June 2014 .

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