The Himalayan range, topped by 29,035-foot (8,850-meter) Mount Everest, the highest mountain in the world, is one of the largest and most distinct geographic features on the earth's surface. The range, running northwest to southeast, stretches 1,400 miles (2,300 kilometers); varies between 140 miles and 200 miles wide; crosses or abuts five countries-India, Nepal, Pakistan, Bhutan, and People's Republic of China; is the mother of three major rivers-Indus, Ganges, and Tsampo-Bramhaputra rivers; and boasts over 100 mountains higher than 23,600 feet (7,200 meters)-all higher than any mountains found on any other continent.
The Himalayas Created by the Collision of 2 Plates
The Himalayas and Mount Everest are young geologically speaking. They began forming over 65 million years ago when two of the earth's great crustal plates-the Eurasian plate and the Indo-Australian plate-collided. The Indian sub-continent steamed northeastward, crashing into Asia, folding and pushing the plate boundaries, and steadily shoving the Himalayas over five miles high. The Indian plate, moving forward about 1.7 inches a year, is being slowly pushed under or subducted by the Eurasian plate, which obstinately refuses to move, forcing up the Himalayan range and the Tibetan Plateau, both rising from 5 to 10 millimeters a year. Geologists estimate that India will continue moving northward for almost a thousand miles over the next 10 million years.
Light Rocks are Pushed Up as High Peaks
Heavier rock is pushed back down into the earth's mantle at the point of contact, but lighter rock, like limestone and sandstone is pushed upward to form the towering mountains. At the tops of the highest peaks, like Mount Everest, it is possible to find 400-million-year-old fossils of sea creatures and shells that were deposited at the bottoms of shallow tropical seas that are now over 25,000 feet above sea level.
"The Summit of Mt. Everest is Marine Limestone"
The great nature writer John McPhee wrote about Mount Everest in his book Basin and Range: "When the climbers in 1953 planted their flags on the highest mountain, they set them in snow over the skeletons of creatures that had lived in the warm clear ocean that India, moving north, blanked out. Possibly as much as twenty thousand feet below the seafloor, the skeletal remains had turned into rock. This one fact is a treatise in itself on the movements of the surface of the earth. If by some fiat I had to restrict all this writing to one sentence, this is the one I would choose: The summit of Mt. Everest is marine limestone."
Mount Everest's Geology is Simple
The geology of Mount Everest then is very simple. The mountain is a huge slice of solidified sediments that once lay at the bottom of the Tethys Sea, an open waterway that existed between the Indian sub-continent and Asia over 400 million years ago. The sedimentary rock was slightly metamorphosed from its original deposition and then lifted upward at an amazingly speedy rate-as much as 4.5 inches (10 centimeters) a year as the Himalayas rose.
Sedimentary Layers Form Most of Everest
The sedimentary rock layers found on Mount Everest are limestone, marble, shale, and pelite that are divided into rock formations; below them are older rocks including granite, pegmatite intrusions, and gneiss, a metamorphic rock. The upper formations on Mount Everest and Lhotse are filled with marine fossils.
Three Distinct Rock Formations
Mount Everest is composed of three distinct rock formations by geologists. From the mountain base to the summit, they are: the Rongbuk Formation; the North Col Formation; and the Qomolangma Formation. These rock units are separated by low-angle faults, forcing each one over the next in a zigzag pattern.
The Rongbuk Formation at the Bottom
The Rongbuk Formation composes the basement rocks below Mount Everest. The metamorphic rock includes schist and gneiss, a finely banded rock. Intruded between these old rock beds are great sills of granite and pegmatite dikes where molten magma flowed into cracks and solidified.
The North Col Formation
The complex North Col Formation, located between 7,000 and 8,600 meters, divides into several distinct sections. The upper 400 meters composes the famous Yellow Band, a yellowish brown rock band of marble, phyllite with muscovite and biotite, and semischist, a slightly metamorphosed sedimentary rock. The band also contains fossils of crinoid ossicles, a marine organism with a skeleton. Below the Yellow Band are more alternating layers of marble, schist, and phyllite. The lower 600 meters is composed of various schists formed by metamorphism of limestone, sandstone, and mudstone. At the bottom of the formation is the Lhotse detachment, a thrust fault that divides the North Col Formation from the underlying Rongbuk Formation.
The Qomolangma Formation at the Summit
The Qomolangma Formation, the highest rocks on the summit pyramid of Mount Everest, is formed by layers of Ordovician-age limestone, recrystallized dolomite, siltstone, and laminae. The formation starts at 8,600 meters at a fault zone above the North Col Formation and ends on the summit. The upper layers have many marine fossils, including trilobites, crinoids, and ostracods. One 150-foot-thick layer at the bottom of the summit pyramid contains the remains of micro-organisms including cyanobacteria, deposited in shallow warm water.