Geoscience Reference
In-Depth Information
Plate 24.8
Nappes or klippes, thrust from left to right by the advancing African plate, exposed in the higher zone of unglaciated
peaks (centre foreground) in the Pennine Alps of south-west Switzerland.
Photo: Ken Addison
Tibetan plateau rising to the north (
Figure 24.12
).
Indentation accommodates head-on crustal shortening by
expelling continental crust laterally, raising other ranges
subparallel to its path like a bow wave. The Hindu Kush
(west) and Hengduan Shan (east) are therefore parts
of the indentation system, whereas interior thrust and
strike-slip forming the Kunlun Shan and Tien Shan
ranges, north of Tibet, lie ahead of it. The Himalayas and
Karakoram ranges support many peaks over 7 km high
and several above 8 km, including Everest (8,848 m), K2
Godwin Austen (8,611 m), Kangchenjunga (8,586 m),
Makalu (8,475 m), Dhaulagiri (8,172 m), Annapurna
(8,078 m) and Gasherbrum (8,068 m). Indentation rates
of 2-5 cm yr
-1
and tectonic uplift of 4 m kyr
-1
ensure that
the Himalayas are among Earth's most geomorphically
active areas. Evergreen forest grows at 2,500 m OD on
southern slopes in annual average temperatures of 10
The Tethyan orogens, especially the Himalayan ranges
and Alps, lie along the zonal climatic divisions of Asia and
Europe. This accentuates meridional, north-south
thermal contrasts by limiting heat and moisture transfers,
especially in Asia, where the Himalayas and Tibetan
plateau inhibit northward penetration of the monsoon.
Although exerting less emphasis on global atmospheric
circulation than American cordilleras, the elevation and
size of the Tibetan plateau profoundly disturb the Asian
subtropical jet stream, with major impacts on hemi-
spherical climate. All ranges support alpine glaciation and
mountain ice caps (
Himalaya
means 'land of snow and
ice' in Sanskrit) and source some of the largest rivers in
Eurasia. Their relatively large human populations place
them under particular environmental stress.
C
but appears as sub-fossils in Pliocene sediments 5,900 m
high and at -9
New Zealand: Southern Alps
The Southern Alps afford an outstanding example of the
relationship between contemporary tectonics and young
mountains, despite their smaller scale. New Zealand
occupies a microcontinental plate astride convergent
Indo-Australian and Pacific plates. The Pacific plate is
C in the northern Himalayas. This, and the
occurrence of only the latest Pleistocene glaciation in the
Nan Shan range, is powerful evidence of the continuing
rapid uplift of these mountains.
