Travel Reference
In-Depth Information
FROM SEABED TO SNOW CAPS: THE RISE OF TIBET
Some 50 million years ago, the Indian and Eurasian plates collided. What happened next
in the long development of the Tibetan plateau is the subject of much debate.
'There are several different ideas,' says geologist Kristen Cook, who has been studying
the plateau for the past 11 years. 'One possibility is that large chunks of Eurasia were just
pushed out of the way towards what is now southeast Asia. Another is that the Eurasian
crust just piled up in front in India, crumpling up in folds and faults until it became ex-
tremely thick. It's also possible that, rather than a simple collision, the lower part of the
Indian crust was shoved underneath the Eurasian crust and kept moving northwards; this
would mean that there could be bits of India sitting below central Tibet today. Most likely,
a combination of these things happened, but we need more evidence to know for sure.
There is even renewed debate in the past year or two about the timing of the India-Asia
collision, which was one of the few things we thought was pretty settled.'
Of course 'settled' is not a word usually associated with the plateau. India moves to-
ward the rest of Asia at a rate of about 4cm each year; the plateau is actually spreading
out rather than getting higher, and devastating earthquakes such as the one that rocked
Yùshù (Jyekundo) in Amdo in 2010 killing 2700 people testify to the powerful tectonic
forces still at play.
For those interested in the geological history of Tibet, the boundary between India and
Eurasia can still be seen in the geology around the Yarlung Tsangpo River. 'You'll find rocks
here,' says Cook, 'that came from deep below the floor of the ocean that used to separate
the two plates. Visiting Everest Base Camp on a clear day you may be able to see hori-
zontal layering on the very top of Mount Everest. That's because it's made of limestone -
former ocean floor - that was thrust on top of the rocks above and then lifted all the way
up to the top of the world.'
Indeed, visitors to Shegar may well find locals selling ancient fossils of marine animals
- at 4000m above sea level!
How much Tibetans understand from experience or traditional teachings about their
geology is hard to say, but in Cook's experience, people learn fast and have a lot of natural
curiosity. 'My favourite encounter was with a Tibetan boy who played hooky from his
shepherd duties to come with us as we walked up a river valley in search of some particu-
lar rocks. He was fascinated by our geologic map, soon had it completely figured out, and
then took over and started leading the way, asking questions about the geology of his val-
