Geoscience Reference
In-Depth Information
summer monsoon coincides very roughly with that affected by ENSO events ( Chapter
23 ; Figure 23.1 ). If a year of weak summer monsoon coincides with an El Ni no year,
the result will be a much lower than average summer rainfall. Conversely, if a La
Ni na year coincides with a year of strong summer monsoon, the result can be severe
flooding as a result of unusually heavy summer rainfall, as in 2013.
Dust-storms are common in the drier parts of central Asia and China. Dust is
mobilised during powerful convectional updrafts associated with strong frontal winds
and is carried from eastern Siberia across eastern China, Korea and Japan out across
the Pacific and sometimes as far as the Greenland ice cap, under the influence of high-
level jet streams (Liu et al., 1985 ). Dust-storms originating in Mongolia and western
China tend to occur most frequently during the passage of strong cold fronts in the
Northern Hemisphere spring, when the Siberian high pressure system is weakening
(Middleton, 1991 ;Roe, 2009 ).
19.3 Asian desert landscapes
All of the elements of desert landscapes outlined in Chapters 1 and 2 are present in
Asia but on the grandest of scales. The mountain ranges are huge, the desert dunes are
the highest on the planet and the Loess Plateau of central China is the largest feature
of its kind on earth. Cenozoic tectonic uplift and associated faulting were responsible
for the creation of the Tibetan Plateau - the largest and highest plateau on earth, with
a mean elevation of 4,600 m - as well as the Himalayas, Tian Shan, Kunlun Shan,
the Pamir and Altai mountains, and many smaller ranges. Deep tectonic depressions
between these ranges, such as the now almost waterless Tarim Basin bounded to
the north by the Tian Shan and to the south by the Kunlun Shan, are occupied by
hyper-arid deserts like the Taklamakan or the Badain Jaran Desert to the east, which
is in turn bounded to the south by the Qilian Shan, a major supplier of sediment to
the desert ( Chapter 8 , Figure 8.12 ). In common with deserts elsewhere, the mountain
ranges are flanked by alluvial fans but on a vast scale. These fans sometimes grade into
gently undulating to nearly level elevated stony plains or plateaux, like the Alashan
Plateau in north China's Inner Mongolia or the great Gobi Desert of northern China
and Mongolia, which covers an area of 1.3 million km 2 and is the largest desert in
Asia.
The sediments derived from the alluvial fans were reworked at intervals during the
late Cenozoic to form the great sand seas of the Taklamakan, Badain Jaran and other
deserts in China and, on a much smaller scale, the now mostly fixed sand dunes of the
Thar Desert of India. Between these dunes, there are remnants of former river channels
and occasional saltpans or small lakes. In the case of the Badain Jaran Desert, more
than 100 lakes occupy hollows between the high dunes, and are fed by groundwater.
Some of the salt lakes are huge, such as Lake Qinghai near the city of Xining in
western China. The former pluvial Lake Lop Nor between the Gobi Desert to the
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