Forbidding and at the same time inspiring, the snow-covered peaks of the highest mountain range in the world are reared against the sky like an immense impenetrable barrier.
The local people long ago named the mountains himalaya—Sanskrit for “abode of the snow” Few descriptions are better drawn. The Himalayas are the highest mountains in the world, with more than 30 peaks rising to heights of 24,000 feet (7,300 meters) or more. These majestic summits tower over tiers of lower ranges and reach far above the level of perpetual snow. Many of the permanent snowfields, one of the range’s most distinctive features, give rise to immense glaciers as well as some of the mightiest rivers in Asia, including the Ganges, Indus, and Brahmaputra.
The Himalayas are actually a series of three parallel ranges marked by jutting, snow capped peaks, deeply eroded river gorges, and immense valleys, many of which were carved by slowly creeping glaciers. The ranges sweep almost without interruption in a great northwest-to-southeast crescent some 1,500 miles (2,400 kilometers) long between the Tibetan Plateau and the Indo-Gangetic Plain of northern India. They touch parts of India, Nepal, Pakistan, Bhutan, Sikkim, and China, and cover an area comparable to that of France.
The southernmost range, the Siwa-lik Hills, has a maximum altitude of about 5,000 feet (1,500 meters) and is indented by many flat-floored valleys called duns. The middle range, the Lesser Himalayas, varies in altitude from about 7,000 to 15,000 feet (2,100 to 4,600 meters) and is crossed by valleys whose floors lie some 3,000 feet (900 meters) above sea level. One of them, the Vale of Kashmir, is considered to be one of the most picturesque mountain valleys in the world.
The awesome spine of the moun-tains is the Great Himalayas. The most northerly range, it is a lofty, rugged chain reaching high above the line of continual snow. Its spectacular peaks include many of the highest in the world—Mount Everest, the highest point on earth, at 29,028 feet, or 8,848 meters; Kanchenjunga, the third highest; and many more. (The second highest mountain, K2 or Mount Godwin Austen, is in the Karakoram Range, sometimes considered a fourth range of the Himalayas.) Nine of the 14 highest mountains on earth are in Nepal, where the Great Himalayas reach their maximum heights.
Surprisingly, much of the “rooftop of the world” was formed beneath the sea millions of years ago. An ancient ocean named the Tethys Sea, after a figure in Greek mythology, once lay roughly where the Himalayas are now Rivers entering the sea carried in debris from the surrounding land, and marine animals died and contributed their skeletons to the sediments accumulating on the ocean floor. Eventually the sediments piled up in beds as much as 6 miles (10 kilometers) thick and were compacted into limestone, shale, and several other kinds of sedimentary rock.
Some 200 million years ago most of the earth’s landmasses were united in a single supercontinent called Pangaea. About 135 million years ago Pangaea began breaking up, and various sections of it, so-called tectonic plates, began drifting in different directions, moved by pressures from deep within the earth.
The plate forming the Indian sub-continent moved slowly toward the Asian mainland, and finally, about 65 million years ago, the two started to collide. The force of the collision wrinkled and folded the sedimentary rock layers of the former Tethys Sea, but in this case the wrinkles were of colossal size. The process was some-what similar to two pieces of ice col-liding on a frozen river and pushing up a rim of shattered ice at the point of the collision. In many places the heat and pressure of the collision melted the sedimentary rocks and changed them into gneisses, schists, and other metamorphic rocks.
As the Himalayas rose, they were attacked by the elements—wind, rain, snow, and extremes in temperature. During the ice ages great glaciers sculpted the mountains, sharpening peaks and deepening valleys. During warm interglacial periods, melt water from the glaciers cut deep chasms and carried immense loads of ‘sand and gravel downhill.
Today we see the results of all these forces acting over the course of mil¬lions of years. Each step in the history of the Himalayas can be read in the mountains’ rock layers, terraced val-leys, and scarred cliffs.
And the story has not yet ended, for the Himalayas are still growing. Be¬fore the British expedition climbed Mount Everest in 1953, a geologist studying the growth of the mountains jokingly told the mountaineers that they had better hurry to the top be¬fore Everest grew any higher. More seriously, the continuing upheaval of the mountains sometimes produces landslides that claim the lives and property of mountain dwellers.
Although geologists have been try-ing for some time to calculate the Himalayas’ growth rate, the task is complicated, since accurate calcula-tion of their height in the past is difficult. One estimate is that they have risen more than 4,000 feet (1,200 meters) in the past 11/2 million years.
At present, geologists believe, the mountains are probably rising at a rate of about 3 to 4 inches (8 to 10 centimeters) per year. But while the pressures pushing the Himalayas up are still at work, so too are the forces wearing them down. In fact most of the mountains’ upward movement is continually erased by erosion. Thus geologists believe that the net growth of the Himalayas amounts to only 1 to 2 inches (2.5 to 5 centimeters) over the course of a century. Sarah lives in the Czech Republic and spends her time traveling and writing websites.