Everest Here Continents Collided. Alex W Milne
on a trek through the foothills of the Khumbu up into the high mountains. The armchair enthusiast will gain a deeper insight into how the mountains formed and how they look. The trekker will see, at every twist and turn, how these mountains and glaciers evolved and with it a deeper understanding that will enrich the experience of walking through the incomparable Khumbu.
I have visited Nepal on two occasions. The first was in 1980 when I crossed the Thorung La with John Wood in December to complete the Circum-Annapurna trek. One of the first westerners to do so. The Nepalese government until then were very reluctant to allow trekkers into this area, because of the poverty of the local population. They felt that foreign visitors would exacerbate the then shortage of food in the area. In Stan Armington’s seminal trekking book on Nepal he states that when you return home from Nepal, you will mortgage your life to return. Well truth to say, it was a further thirty years before I returned, but I always knew I would. It remains the single most spectacular country I have visited. Put simply, Nepal has it all. Wonderfully warm, open and friendly people, despite or indeed perhaps because of, all their undeniable hardship. Amazing scenery. A wonderful climate.
In the intervening years Nepal has been through a huge turmoil having fought a recent 10 year civil war. The Royal Family has been deposed and the government is now struggling to establish a stable democracy. It is a country that is so poor that it fails to provide the most basic services. In Kathmandu 80% of children go to school, however in the countryside it is significantly less, at 40%.
Thirty years ago there were only a handful of restaurants and hotels in Thamel and the electricity supply was off more often than it was on; candle lit diners were a necessity and added to the atmosphere. The only motorised vehicles were taxis. These days, Kathmandu has expanded into a thriving metropolis of probably a million people and with it the problems of most modern big cities. Arriving in the evening and crossing the city to the Vajra Hotel was like arriving in any other third world country. Roads were choked with traffic jams. Pot holes impeded the flow of traffic and the pollution was nauseating. What I find extremely sad about Kathmandu is the motor car and motor bike congestion in the old city. It is clearly out of control and the pollution only adds to the challenges that the city faces in the future.
Chapter 1
Plates Collide
The Himalaya is a continental collision of epic proportions. The product of the collision between the Indian plate to the south and the Eurasian plate to the north, that started 70 million years ago, as India headed towards Eurasia, consuming the intervening Tethyan ocean. The collision is ongoing today. It is a collision full of amazing features:
To the north the Tibetan Plateau has been uplifted 5 kms from sea level.
The average height of the Himalaya is also 5kms. Evidence of continental thickening.
An estimated 2000 - 2500 kms of convergence between the Indian and Eurasian continents over a 50 million year period (see diagram below). Followed by 20 million years of collision. On the geological timescale a relatively recent event.
The Himalayan mountains are formed by crustal faulting and uplift. In any plate tectonic reconstruction a key feature is the the recognition of the suture, or join, between colliding continents. The location and nature of the suture is illustrated in the cross section below. The suture between the two plates is believed to be the Indus Tsangpo suture in southern Tibet. This assumption is based on the presence of marine Tethyan ocean sediments within the suture.
What are the rocks in the collision zone? How old are they? In the case of the Himalaya a model of crustal scale thrusting has been developed. The father of this model was the Swiss geologist Emile Argand, crucially, he postulated that India was subducting, i.e. pushing beneath, Eurasia and creating the Tibetan plateau. Subsequently the nature of the thickening was debated in the 1970 and 1980’s by John Dewey and Molnar and Tapponier, Philip England and Greg Houseman. Molnar and Tapponier believed that the Tethyan oceanic crust was largely extruded or squeezed sideways, whereas Dewey believed that the oceanic crust was accreted onto the passive Indian continental margin.
More recently the work of Mike Searle at Oxford University has demonstrated how the accreting leading edge of the India plate has been uplifted and thrust through time. It is these rocks and geological structures that you observe while walking from Lukla up to Everest. The trekker is in effect walking directly into and observing the products of the continental collision. He is walking into and viewing a spectacular example of the Earth's crust that has been brought to surface from 20 kms down and folded and faulted and thrust during 20 million years of continent to continent collision.
Ideally if time allows, I recommend you take the Everest flight first and see it all on a grand scale. The immense size and complexity of the Himalayan chain is clear to see from 20,000ft. What you see is the smashed up Earth's crust on the leading edge of the India plate.
Fifty million years getting there and then 20 million years building the Himalaya. - Source USGS.
Modified from the USGS. This diagram illustrates how, during collision, the Indian plate has subducted beneath the Eurasian plate. Over time the India plate has fragmented and been thrust back up to form the high Himalaya. As the Indian plate has pushed on the Eurasian plate the Tibetan Plateau has been uplifted. A remnant of the ancient oceanic crust has been trapped and preserved in the Indus Tsangpo suture zone.
Haze along the Himalaya
The Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image in 2008. The image shows how narrow a strip the Himalaya occupies and how mountainous the Tibetan plain is compared to the Indian plain. This is because the Indian plate is pushing against the Eurasian plate causing it to uplift and buckle. The red dots are probably fires seen from space.
Chapter 2
Mountain Building
Here Continents Collided
The Himalaya is a “must see”, lifetime experience. I first visited the Himalaya in 1980 as a newly graduated geologist. I had an ambition to see the highest mountains in the world. My first view was of Manasulu on the Jiri to Manang trek. It is a view that is still etched in my mind. Manasulu looked glorious as it glowed in the setting sun.
The Himalaya has evolved from a continent to continent collision that has long fascinated geologists. The trek into Everest takes you directly into the collision zone. What does the “roof of the world" comprise and how was it made? These questions have challenged and continue to challenge successive generations of geologists.
British geologists were involved in the first attempts to climb Everest and at the same time they gathered rock samples high on the mountain for analysis. This along with field observation began to unravel the evolution of Everest. The most notable in mountaineering terms of the early geologists were Noel Odell and Lawrence Wager, both of whom subsequently followed academic careers. Odell at Cambridge and Wager at Oxford. It is my lasting regret that I never had the opportunity to meet Odell who was regular attendee at the Alpine Club, even into his advanced years. It was a great privilege to attend club meetings with Lord and Lady Hunt, George Band, Mike Ward and Mike Westmacott. As a younger generation of mountaineers we were, and still are, in awe of the “Golden Generation”.
Everest from Gokyo Ri. Showing location of geological samples recovered by mountaineers and