By Carolyn Fry



The Himalayas are the result of the collision of two tectonic plates

"I have some samples here in my office where you can still see tiny fragments of coral and conodonts which were once swimming around in an ocean somewhere near the equator," explains Dr Mike Searle, Research Fellow at Oxford's Department of Earth Sciences.

These marine sediments lie atop sedimentary and igneous rocks which have been baked by high temperatures and pressures into crystalline metamorphic rocks.

Many rocks around the base of Everest are unique granites containing unusual minerals such as tourmaline, garnet and mica.

Conveyor belt system

The strange juxtaposition is caused by the ongoing collision between two vast slabs of continental crust.

The Indian plate is moving northwards and piling into the Asian plate, in the process pushing rocks deep down into the crust. This subduction is in turn forcing the rocks above upwards - including those around Everest.

Two shallow faults slice through the mountain and over millions of years, subducted rocks have been transported above the higher fault and jacked up to form the higher Himalayan peaks.

"Rocks are progressively subducted to the north, transferred above the fault and then progressively extruded to the south. The top of Everest is literally the uppermost layer of this extruding channel."

Dr Searle visited Everest five times from the Nepalese side and once from Tibet to gather information for the map.

As well as identifying rocks in the field, he gathered 400 samples for chemical analysis and examined aerial photographs and satellite images to map inaccessible areas.

The map took six years to compile

"You can walk around Everest, Nuptse and Lhotse up over to Cho Oyu in the west and Makalu in the east and you can get a real hold on the 3D geometry of the rocks.

"That is very difficult to do in any other part of the world."

You can buy a copy of the geological map of Everest directly from Dr Searle.

As well as the map itself, the poster includes photographs of the Everest massif, a panorama taken from a balloon over the Kangchung Valley, an Aster satellite image and cross-sections explaining the structure of the Himalayas.