Permafrost

ottom at a rate of 4 cm/year and accelerated to 9 cm/year after 2000.
Thermokarst investigations have shown that new thermokarst is forming in undisturbed
areas of the Tanana River, Little Tok River, and Slana River (a tributary of the Copper River)
valleys, and in the Wrangell Mountains indicating warming and thawing of the permafrost in
these areas.
Massive ice wedges on Alaska’s North Slope that have been stable for thousands of years
have been thawing during the recent warming.
The primary causes of the recent permafrost warming appear to be increased air
temperatures, and increased snow covers with snow cover the dominant factor during the late
1980s and 1990s In some parts of the state.
Key words: Permafrost, borehole temperatures, climate warming, thawing, thermokarst,
monitoring.
Thermal State of Degrading Permafrost in the Source Region of Yellow
River, Qinghai Province, China: Numerical Approach
T. Sueyoshi 1 , A. Ikeda 2 N. Matsuoka 3 and T. Ishii 4
(1. Institute of Low Temperature Science, Hokkaido University; 2.National Institute of Polar Research,
Japan, Research Fellow of the Japan Society for the Promotion of Science; 3.Graduate School of Life
and Environmental Sciences, University of Tsukuba, Japan; 4.Geological Survey of Japan, National
Institute of Advanced Industrial Science and Technology, Japan.)
Abstract: A large part of the source area of the Yellow River (Hunag He), in the northeastern
margin of the Tibetan Plateau, is underlain by perennially or seasonally frozen ground, which
faces a rapid warming in the past decades. Since 2002, we have investigated the permafrost
distribution in the area to evaluate permafrost degradation and its impacts on groundwater
hydrology. In this study, based on the data obtained during the first two years (Ikeda et al, 2006),
involving the temperature profile from the 8m-depth borehole, the surface temperatures from
distributed small loggers and the geophysical soundings, thermal history of the permafrost in the
area was investigated through parameter studies using the numerical model.
The problem was defined as the one-dimensional thermal conduction with phase change
under the forcing of the surface boundary condition, which was given as ground surface
temperature variations. Stable geothermal heat flux and homogeneous physical soil properties
were assumed. Starting from various initial conditions, the rate of permafrost degradation was
calculated under the different surface temperature history. Giving the same surface temperature
conditions, the rate of degradation could vary even for the identical-thickness permafrost,
depending on the initial temperature profile. Hence, several initial conditions as well as surface
temperature scenarios are examined in the calculations to estimate the rate of degradation in the
source area.
In the previous studies, permafrost thicknesses in the source area in 1980s are reported as
ca.10m or even less depending on the sites, which must have been already warm permafrost.
Therefore, the reasonable initial temperature profile would be zero degree (or freezing point)
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