Geology Reference
In-Depth Information
RUSSIA
KAZAKHSTAN
Alma Ata
Urumqi
Ulaan Bator
Harbin
MONGOLIA
NORTH
KOREA
Beijing
SOUTH
KOREA
Golmud
Lanzhou
CHINA
High-latitude permafrost
Continuous zone
Discontinuous zone
Island or isolated
permafrost
Lhasa
Chengdu
Seasonally-frozen ground
Southern limit
High-altitude permafrost
Continuous permafrost
zone in the plateau
Isolated permafrost
Alpine permafrost
0
1000
km
Figure 5.9.
Permafrost distribution in China and adjacent areas of Mongolia and Kazakhstan.
Compiled from Shi (1988), Brown et al. (1997), Brown (2001), and Aubekerov and Gorbunov
(1999).
continuous permafrost, as defi ned in North America, does not exist on the Tibet Plateau.
Equally, montane permafrost differs from alpine permafrost because alpine permafrost
is characterized by steep slopes and bedrock terrain. By contrast, the Tibet Plateau has
relatively low surface relief in between the various mountain ranges and can be underlain
by as much as 1000 m of unconsolidated sediments (Guo et al., 1982). Large mountain
ranges separate many of the basins. Thus, the vastness and unusual nature of this terrain
defi es easy classifi cation in terms of either alpine or latitudinal permafrost.
As a generalization, we can characterize montane permafrost as being a few meters to
over 100 m in thickness. The mean annual ground temperature (at the depth of zero-
annual amplitude) varies between 0 °C and
3.5 °C. Therefore, it is similar in temperature
to much alpine permafrost but considerably warmer than most latitudinal permafrost.
Some studies report that the thickness of Tibet Plateau permafrost increases at a rate
of between 10 m and 30 m for each one degree increase in latitude (Tong and Li, 1983).
This is not supported by ground temperature measurements, because air temperature
varies irregularly with latitude and is dominated by altitudinal effects. Permafrost is
known to thicken with increasing altitude at a rate of 15-20 m for each 100 m increase in
elevation (Shang, 1982; Tong and Li, 1983; Zhou and Guo, 1982). A unique characteristic
of Tibet Plateau permafrost is the increase in its lower altitudinal limit from north (at
4200 m a.s.l.) to south (at 4800 m a.s.l.), at a rate of about 110 m per one degree of latitude.
In general, the lower altitudinal limit of permafrost on the Plateau is usually 800-1100 m
lower than the snowline (Zhou and Guo, 1982). The mean annual air temperature at the
lower limit is in the range of
−
−
2.5 °C to
−
3.6 °C (Tong and Li, 1983). This is considerably
