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.