Helpful Diagrams

The Himalayan Mountains span the countries of Pakistan, India, Nepal, and Tibet

The Indian plate is converging with the Eurasian plate, creating the Himalayas

The path traveled by the Indian plate over the last 100 million years

Side-view of the Indian-Eurasian collision, producing the Himalayas

Side-view of continent-continent convergence

The Orogeny of the Himalayan Mountains

Introduction

The Himalayan Mountains are some of the most beautiful features of nature and are today home to many different groups of people. The mountains span the countries of India, Nepal, Pakistan, and Tibet in South Asia and are the location of the tallest mountains in the world. The Himalayan Mountains, however, have not always been the natural wonder that they are today. 100 Million years ago, in fact, the whole Indian sub-continent, sans Himalayas, was its own island.

Farming the slopes of the Himalayas, Nepal

How the Himalayas Formed

The present-day continental formations on the world are, geologically speaking, relatively recent formations. 250 Million years ago, the continents were part of one giant super-continent, called Pangea. Due to plate tectonics, the crustal plates of the earth moving independently, pushing and pulling into one another and creating constant geologic activity, the continent of Pangea was ripped apart. The new continents slowly spread around the world creating the continents and oceans that we know today. As a part of this ripping apart, the Indian plate broke off from the bottom of Pangea and began to move northward, toward the larger Eurasian plate. India charged across the ocean at a rate of 10 – 15 cm/ year, an unusually fast rate for crustal plates. Over the next several million years, the movement of the Indian plate slowly closed the Tethys ocean that had separated India from Eurasia.

Approximately 55 million years ago, the Indian plate was heading steadily for the Eurasian plate, and approximatley ten million years ago crashed into it (see diagrams at right). The oceanic crust portion of the plate broke off, and, due to a greater density, was subducted underneath Eurasia and incorporated back into the mantle. The continental crust portion of the plate, however, is less dense. Therefore, it would not easily subduct beneath the greater plate. As a result, the two continents continued crashing into each other, with neither able to sink below the other. This collision is what created the Himalayan Mountain belt. The continental crust here is buckling and piling on top of each other to create the largest mountains on the world today. The Himalayan orogeny took between 40 and 60 million years, and is still continuing.

The crust beneath the Himalayan Mountains is between 60 and 780 km thick. This is nearly twice as thick as continental crust over the rest of the world. This thick crust forms what is termed a ‘crustal root’. This root protrudes downward into the mantle and is important for mountains because the buoyancy of the root allows the mountains to achieve their height.

Sunrise in the Himalayas - View from Poone Hill, Nepal

The Future of the Himalayas

The Indian plate is continuing to crash into the continent of Asia. This is happening at an average rate of 2 cm/year, or 2 meters in the next century. The result of this continuing geologic change is periodic earthquakes in the Himalayas from accumulated energy from collision and the continuing growth of the mountains. It is unlikely, however, that the mountains will rise much farther. At present, the peak of Mount Everest, the tallest mountain in the world, is 29,029 feet (8,848 m) above sea level. Although the collision between India and Asia is continuing, erosive forces are also working on the mountain and wearing down the peaks. In addition, as the mountains continue to rise, their massive weight bears down on the crustal root and the rock that is buried in the crust. As this rock as pressed down into the mantle, it begins to melt and flow slowly, and can be squeezed out to the side, causing the mountain to collapse lower.

Global Positioning Systems (GPS) have been important to the geologic research involving plate tectonics and the India-Eurasia collision. It is GPS data that tell us how quickly the geologic change is happening. Using this data, several theorists have put forth that in the next 10 million years, India will plow forward another 150 - 200 km, roughly the width of the country of Nepal. This means that in 10 million years, Nepal as we now know it may no longer exist due to the powerful geologic forces of our earth. Several scientists also believe that the Himalayan region is due for some very powerful earthquakes to relieve the stress created by collision on the Himalayan arc. It is believed that a large earthquake in this region poses a serious threat for over 50 million people.

Mt. Dhaulagiri (above), Mt. Everest (above, right)

Mt. Kanchenjunga (above), Mt. Machhapuchhre (above, right)

To see more pictures from my trek through the Himalayan Mountains, click here.

References

Pictures not referenced via links to original website were taken by Marissa Pine, December, 2001

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Copyright © 20031 Earlham College. Revised 25 February 2003. Send corrections or comments to pinema@earlham.edu