Hello. My Name is David Schultz. Welcome to Our Earth. Its Climate, History and Processes. In this lecture I want to talk about the Himalaya mountains. I want to talk about the plate tectonics that created it I want to talk about the climate change that resulted because of the rising Himalayas. And how this also affected the weather? The Himalayan Mountains are a result of a collision between two continents. In this case, the Indian continent and the Eurasian continent. And in this picture you can see the multiple ridges of high peaks that exist there. And we'll be able to explain why those multiple ridges exist later in this lecture. Recall that the Himalayan Orogeny was just part of a larger Orogeny. The Alpine-Himalayan Orogeny, a result of the continents in the Southern Hemisphere, Africa, India colliding with Europe and Asia, the Eurasian Continent. So let's focus on the Himalayan orogeny. And I want to show you an animation that was created by Robert Hall, of the Royal Holloway University of London. So initially here, 169 years ago we have India down here and South, connected to Australia. Also recognize that there's Greater India 1 and Greater India 2, two other pieces of the continent of India that are no longer in existence. To the north, you have the Eurasian continent up here. As time progresses, you see subduction occurring within this region in the Tethys Ocean. And you see India separate from Australia, rotate counter-clockwise and begin to move northward. This is also in association with this spreading center that's forming in between Indian and Australia, helping to drive the two of them apart. 75 million years, 670 65 around the time of the end of the cretaceous. The extinction of the dinosaurs we see India beginning to approach the Asian continent. We also see the Arabian peninsula in Africa appear over to the west. By 45 million years ago India has reached Asia. And these two continents have begun to collide. You see the loss, the compression of Greater India into Asia, pushing Asia further and further east, and raising the Tibetan Plateau and the Himalayas. And so here we are at the present, with India fully in placed on the Asian continent. So in cross-section, this is what it would have looked like. Here, the Indian Plate is in red, Eurasian Plate is in gray. As these two plates collided, and continental crust was trying to be forced underneath the Eurasian continental crust, the plate began to split up into what are called overthrust faults. And you can see the shearing here, and the production of multiple ridges along the Himalayas. As we've shown with Greater India 1 and Greater India 2 in those previous maps. Over 2,00 kilometers of Indian plate has been lost due to the compression, the continent, continental collision and this overthrusting. This resulted in thickening of the continental crust. Over India to thicknesses, now approaching 70 kilometers, twice its normal thickness. This increasing pressure on the crust also melts rock, and produce granite batholiths and volcanoes in the Himalayas. The other 50% of the Indian plate is lost due to pushing China and Mongolia eastward along faults. And forming the great sedimentary basins in Western China. So what is the impact of the rise of the Tibetan Plateau in the Himalayan Mountains? It's frankly altered global climate. So this mountain building has lead to increased weathering. The increased weathering is a result of the atmospheric carbon dioxide being dissolved in rain water, producing a slightly acidic rain water. This acidic rainwater then leads to the dissolution, and the weathering of the Himalayas and the Tibetan Plateau. These weathered sediments, these dissolved salts are carried by the Great Asian rivers into the ocean. These Asian rivers carry 25% of all the dissolved salts that enter the ocean, just within this small area. So this is an incredible contribution to the salt balance of the oceans. The reduction, and the production of all this rain by the rising mountains, reduces the amount of carbon dioxide in the atmosphere, reducing the concentration of one of the crucial greenhouse gasses in the atmosphere. Without that extra carbon dioxide, the atmosphere will cool. And we can see that when we look at the record of climate change over the Phanerozoic. Here is the graph that we've seen before of the temperature. And at the end of the Mesozoic the temperature was rather warm, and has declined since that time. The collision of India with Eurasia happened at a crucial point in this decline. And is seemingly related to a more rapid decrease in the temperature in the last 50 million years. Now the rise of the Tibetan Plateau and the Himalayas have also altered the global weather. We've talked about the mountain building and how the high terrain has altered the position of the jet stream. And where this jet stream dips equatorward, cold air moves equatorward. Where the jet stream moves poleward, warm air moves poleward. So to summarize today's lecture, we talked about the Alpine-Himalayan Orogeny as a result of collisions of plates. Plates from the southern hemisphere impacting Europe and Asia. Specifically, the Himalayas resulted from the continental collision that shortened India and extended Asia. And then we saw that the rising of the Himalayas led to global cooling. In a later lecture, we'll see how the rising of the Himalayas also led to a local cooling in Eastern Asia.
