“OROGENOUS ZONE”
THE FORMATION OF THE HIMALAYAS
55 million years ago
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| Formation of the Himalayas. Subduction is the process that takes place when one tectonic plate is pushed downward beneath another. This image of India and the Himalayas notes that subduction occurred when India collided with Asia, which caused the uplifting and subsequent rise of these mountains. Credit: Image by NASA/ Wikimedia Commons. |
Most mountain ranges were created by the collision of one of the earth’s moving plates with another, producing uplift or “orogeny.” Around 167 million years ago the Indian subcontinent (connected then to Australia and Madagascar) broke off of Africa and subsequently began drifting eastward, then broke off of Australia and started drifting northward, culminating in a massive collision with Asia starting around 55 million years ago. This crunching together of two continental plates, the Indo-Australian Plate and the Eurasian Plate, began slowly but surely to create the highest mountain range in the world today, with the peak of Mount Everest reaching 29,028 feet above sea level. The creation of the Himalayas radically affected the courses of river systems and created a major biogeographical barrier for plants and animals, including our ancestors, and has drastically affected not only Asian climate, but likely that of the entire planet.
The impact of the Himalayas on large-scale climate and on today’s human populations has been tremendous. Especially during the past ten million years, as the Indian subcontinent continued the process of slamming into Asia, the Himalayas continued their rise to an elevation of over five miles and the Tibetan Plateau rose to a height of over two miles, profoundly affecting wind, precipitation, and overall weather patterns in much of Asia.
By at least 8 million years ago, the Himalayas and the Tibetan Plateau had risen so high that they served as a barrier to wind patterns, effectively producing monsoonal seasons in much of southern Asia and keeping that region protected from northern frigid air, but meanwhile keeping moisture-laden air from penetrating inland and leading to extremely dry desert regions in much of central Asia, such as the Gobi and Mongolian Deserts. Then the evolution of such deserts in turn led to patterns of great dust storms across eastern Asia, creating deposits of fertile, wind-blown loess that populations in China and much of eastern Asia rely on for food production. Without the Himalayan uplift, agricultural fertility in this region would have been severely reduced. This tremendous continental uplift also seems to have contributed to the cooling in earth’s climate that led to the onset of Ice Ages that about 2.5 million years ago, as the influx of dust into the atmosphere blocked some of the sun’s rays, and increased erosion and weathering of silica-rich rocks in the Himalayas sucked CO2 out of the atmosphere, producing a ‘reverse greenhouse effect’ and cooling the planet.
Last but not least, the Himalayas are also the source of many major rivers in Asia, providing fresh water to billions of people today. That means that billions of people are relying on the maintenance in the Himalayas and the Tibetan Plateau of glaciers and ice packs to feed these rivers and provide their populations with water essential for life.
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| This is an illustration of Himalayan orogeny, which is the movement of the Indian Plate as it collided with the Asian Plate, starting between 60 and 50 million years ago, causing the formation of the Himalayan Mountains. Credit: Illustration by Ashwatham/ Wikipedia. |
HOW DO WE KNOW?
Our knowledge of plate tectonics, from careful matching of similar geological and fossil rock deposits, indicates that the Indian subcontinent broke off of Africa and collided with Asia. Marine fossils bearing animals from shallow sea environments found high up in the Himalayas indicate that these rocks once formed near sea level and were subsequently uplifted thousands of feet.
WHY SHOULD I CARE?
The rise of the Himalayas created a major biogeographical barrier for the entire period of human evolution, as well as changing climatic patterns in Asia and, ultimately, the rest of the world. This uplift also created a very steep barrier to human and animal migrations and movements between southern Asia and much of the rest of Eurasia to the north and east for very long periods of time in prehistory.
WEB RESOURCES
This is an informational site that discusses the geological origins of the Himalayas.
https://library.thinkquest.org/10131/geology.html
This is a more touristy Himalaya website, but still factual.
https://www.himalaya2000.com/himalayan-facts/himalaya-mountain-range.html
This is a definition of the term orogeny.
https://en.wikipedia.org/wiki/Orogeny
