Himalaya, Tibet and the Monsoon

original source: Earth Story, Aubrey Manning BBC

The Himalaya at 8000m at maximum and Tibet with a fairly uniform average of 5000m are a remarkable structure formed by the impact of India into Asia. They dominate the climate of the Indian Ocean in that they create the SW Monsoon. In the summer Tibet heats up causing a low pressure that draws in moist winds from the Arabian sea, these are forced up over India and particularly the Himalaya and the Monsoon results. In the winter the reverse is true, but the high ground effectively blocks out the cold winds from Siberia so that even in winter India is warmer than it should be.

The interesting thing is that although India has been pushing into Asia at a fairly steady rate since the collision started roughly 50mya (only island arcs at that point? Aitchison & Davis), with major uplift occurring in the miocene (25-5mya), the monsoon seems to have suddenly increased at roughly 10mya. See K. S. Valdiya (interesting for the discussion of the influx of grazing animals including various elephant and baboon species with the establishment of grass lands in response to the monsoon and the query as to how they got there through all that high land). Earth Story presented the solution to this as "Pop-up Tibet" the idea that the thickened upper mantle below Tibet fell away at around 10mya and this loss of dense material led to a sudden rise in the Tibetan plateau which is now falling back (evidence the existence of "Normal Faults" on the plateau , also sighted in Greece which was described as slumping into the Med in response to the push of Africa diminishing, fossilised plant material from 11mya showed lower altitudes were likely then). However looking this up online I found this PDF from Spicer using plant material from Tibet to show that it was at its present height 14mya! Spicer says that the likely explanation is that Tibet rose in three steps the southern most first then middle at about 10mya and the north as recently as 3.4 mya.