Permafrost

Permafrost Distribution and Thickness in the South-Eastern Siberian
Platform
Mikhail Zheleznyak
(Melnikov Permafrost Institute SB RAS, Yakutsk, Russia)
Abstract: The primary factors controlling the development and distribution of permafrost are mean
annual temperature at the active layer base or at the depth of zero annual amplitude (t), ground thermal
conductivity (λ) and geothermal heat flow (q).
The existence and evolution of permafrost in the south-eastern part of the Siberian
Platform is determined by climatic, geologic and geomorphic conditions. Despite the low
negative mean annual air temperatures (–6.3°С to –11.4°С), the permafrost temperatures,
distribution and thickness are highly variable over the region. This is attributed to spatial
variations in the heat exchange conditions between the atmosphere, soil and lithosphere, as well
as to variations in λ and q.
The southern part of the Siberian Platform is one of the most intensively studied regions in
Asia with respect to permafrost. Numerous studies conducted since the 1950s revealed the basic
patterns of permafrost distribution. However, lack of sufficient information on permafrost
thickness and position of the permafrost base makes it difficult to comprehensively assess the
present-day permafrost and, hence, to develop reliable paleoreconstructions or predictions of its
future evolution.
During the last twenty years, staff members of the Permafrost Institute, including the
present author, have carried out geothermal measurements in 1,800 boreholes, of which 850
boreholes are deeper than 100 m. These investigations included single, repeated and intensive
geothermal observations. Permafrost thicknesses were determined from ground temperature
measurements in 210 boreholes penetrating through the entire permafrost. This enabled us to
characterize the geothermal field to 3,000 m depth, to compile maps of geothermal heat flow,
permafrost distribution and permafrost thickness, and to construct geothermal profiles of
permafrost 650 to 900 km in extent.
In the study region, ground temperatures at the depth of zero annual amplitude vary from
+2.0 to – 8.0°С, the geothermal heat flux ranges from 20 to 65 mW/m 2 , and the thermal
conductivity varies from 2.3 to 8.6 W/m·K in metamorphic rocks, from 2.2 to 3.7 W/m·K in
igneous rocks and from 1.9 to 6.6 W/m·K in sedimentary rocks. These parameters in
combination control the development of permafrost in the region. Based on measurements, the
maximum permafrost thicknesses occur in the northern Lena-Aldan Plateau (Ulu site) and in
the Olekma-Chara Upland (Udokan Ridge) at 1,900 m elevation, being 720 and 616 m
respectively. The estimated permafrost thickness in the Kodar Range having elevations of
2900-3000 m a.s.l. can reach 1,050 m.
According to permafrost distribution, three hypsometric levels have been distinguished in
the region. The lower level lies between 200 and 600 m isohypses and has continuous
permafrost. The middle level, between 600 and 1,300 m isohypses, is the zone of transition
from the shield to the platform and has discontinuous, frequently thin (50-100 m) permafrost.
The upper level lies above 1,300 m; the permafrost distribution is continuous here. There is a
clear altitudinal trend in permafrost temperature and distribution. Each of these levels has been
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