Geology Reference
In-Depth Information
Continuing up through shattered rock to cross the Lhotse Detachment, the lower of two
fault zones, you'd reach the North Col Formation, which extends up to about 28,200 feet.
This formation consists of 490-million-year-old marble, schist, and phyllite—limestone,
sand, and mud buried deep enough to be pressure-cooked into harder rocks, but not so deep
as to start melting. The mineral assemblage in the North Col Formation shows it underwent
metamorphism just two to four miles below ground, at temperatures of 850-950°F and
pressures of 1,000-2,000 times atmospheric. It was never buried anywhere near as deep as
the rock right below it. Missing are the miles of rock that must have once lain between the
now neighboring rock formations.
At the top of the North Col Formation, a distinctive stripe of yellowish marble (meta-
morphosed limestone) called the Yellow Band cuts across the mountain. At the top of
the Yellow Band, a zone of completely shattered rock defines the second fault zone, the
Qomolangma Fault, which separates the marble below from unmodified limestone of the
overlying Qomolangma (or Everest) Formation. These uppermost rocks also date from
three rocks of Everest were born in the same sea, but they had radically different histories
before being spliced together to form the world's highest mountain.
Standing on the frigid summit of Everest, if you could pick up a piece of the limestone
and view it under a microscope you would find that the top of the world consists of frag-
mented trilobites and tiny fecal pellets that settled to a tropical seabed. Beneath your boots
you'd see the essential truth of the world's highest mountain—the rock at its top once lay
at the bottom of the sea.
How could a scrap of seafloor come to cap the world? Based on the cooling history of
minerals they contain, these rocks started rising from the sea about fifty million years ago,
when India began smashing into Asia. As India moved north, Asia stayed put, crumpling,
folding, and faulting the incoming rock that had been deposited in a shallow sea. Crushed
in a geological vise, the old seafloor was squeezed up and up, rising centimeters a year to
eventually stand more than five miles above the coast. Faults formed as the incoming rock
compressed, fractured, and pushed aside the rock that was already there. The southern edge
of the Tibetan Plateau began to slide down toward India in much the same way that materi-
