Permafrost

174
Permafrost Terrain Analysis along the Tommot-Yakutsk Railway
I.S. Vasiliev, S.P. Varlamov, A.N. Fedorov, M.N. Zheleznyak
(Melnikov Permafrost Institute SB RAS, Yakutsk, Russia)
Abstract: The Tommot-Yakutsk Railway now under construction is 454 km long and passes
through the area between latitude 59° and 62°N and longitude 127° and 130°E. Elevations
range from 100 to 600 m a.s.l. The railway route traverses the terrain with extremely difficult
geocryological conditions. The difficulty is related to the development of adverse processes and
phenomena, especially those associated with frost action. Their distribution, in combination
with environmental factors, is differentiated into seven physiographic regions.
1. The Lena stepped outcrop, dolomite region is characterized by distinctly stepped relief and
by discontinuous occurrence of permafrost. The high amounts of solar radiation and
precipitation in the most southerly region determine the occurrence of unfrozen ground on
elevated well-drained interfluves and warm slopes. Permafrost up to 30 m thick occurs on the
shadowed north-facing slopes, and on the lower slopes and bottoms of small valleys (Figure).
The northern limit of unfrozen ground is indicated by the range of cedar pine and mixed forest
of pine, larch, aspen, birch and occasional cedar pine with undergrowth of mountain-ash.
Ground temperatures (Тg) vary from +1.0 to –2.0°C, depths of seasonal freezing (ξfr) are 2.0 to
3.5 m, and depths of seasonal thawing (ξth) range from 0.8 to 2.5 m. The railway route passes
along the foot of slopes and crosses the bottoms of small valleys, where surface disturbance
would trigger solifluction, movement of rock fields, frost heaving and thaw settlement.
2. The Lena-Aldan rolling watershed, dolomite region is also characterized by dissected
relief, but permafrost with thicknesses of 50 m in the south to 650 m in the north is continuous.
Тg varies from +0.5 to –3.5°С, ξfr from 2.3 to 3.5 m and ξth from 1.2 to 3.0 m. Shallow taliks
are encountered locally on interfluves, warm slopes, burns and forest cuts. Because of the
dominance of surficial clayey silts on the slopes, percolation of suprapermafrost water is
impeded resulting in downslope flow. This leads to accumulation and ponding of
suprapermafrost water on the footslopes and small valley bottoms, causing peat accumulation,
heaving and ice saturation in proluvial-alluvial deposits that are crossed by the railway route.
Surface disturbance will inevitably result in solifluction, mud flows, slumping, thaw subsidence,
and sheet and rill wash.
3. The Lena-Amga rolling, karsted limestone region has less dissected relief and continuous
permafrost with an estimated thickness of 650 to 720 m. Тg varies from +0.5 to –3.5°, ξfr is
2.5 to 3.2 m and ξth is 0.8 to 2.5 m. Both surface and subsurface karst is developed throughout
the region. Surface disturbance in the areas crossed by the railway route causes slumping, mud
flows, solifluction, thaw subsidence, frost heaving, and sheet and rill wash.
4. The Lena-Aldan undulating, sandstone region has continuous permafrost with an estimated
thickness of 400 to 620 m, Тg of +0.2 to –4.0°С and ξth of 0.7 to 2.3 m. The region is a slightly
dissected plateau of the Jurassic mantle of planation blanketed by polygenetic clayey silts
which contain ice wedges in the north and highly kaolinized silty sands derived from
sandstones in the south. Shallow infiltration-radiation taliks are encountered on formerly burned
areas on the interfluves. Poor surface drainage keeps them wet due to infiltration of
precipitation. Solifluction, thermokarst, slope and valley karst are widespread in the region. In