June 30, 2006 — After a rare and arduous journey into a hostile region of western Nepal, geologists have found clues that could upset a popular theory about how the world's largest mountains came to be.
Traveling mostly by foot, geologist Delores Robinson and a handful of colleagues traversed and mapped the rocks in a remote and politically tumultuous region about 125 miles wide and 200 miles long.
Their geological survey among the high mountains and steep valleys has uncovered unexpected details about the Himalayas.
Robinson, who works at the University of Alabama, and her colleagues report their discoveries in the July-August issue of the Geological Society of America Bulletin.
"Some people think the Greater Himalaya rocks were squeezed out like a liquid oozing," said Robinson, describing what's known as the "channel flow" theory.
According to the theory, the ancient seafloor rocks involved in the earliest collision between India and Eurasia began to form the Himalaya chain 55 million years ago.
The collision, which continues today, seemingly first pushed the rocks northward, under Tibet. Heat and pressure then softened the rocks, squishing them between more rigid layers like jelly between crackers.
The deformed remains of these rocks today compose the highest Himalayan peaks, according to the general model.
But large gaps in that theory exist, Robinson said, because much research into the subject has been limited to central Nepal and northern India. So she and colleagues from the University of Arizona and the University of Houston laced their boots, learned Nepali and headed west.
"It was basically backpacking," Robinson said of the field expedition. "The area is so large that you really have to get out and walk."
The elevation of Robinson's study area ranged from 13,000 to 26,000 feet above sea level (4,000 to 8,000 meters), although she restricted her 15-mile-a-day treks to elevations under 16,000 feet.
Along the hikes the researchers collected samples of rocks for laboratory dating, and measured, mapped and photographed the region's unknown geological structure. They used satellite images to follow rock outcrops into areas they could not reach by foot.
"They are looking at an area where there are very few data, ever," said geochemist Matthew Kohn of the University of South Carolina. "What (Robinson) and her co-authors are figuring out is that the structural evolution doesn't support the models as they are right now."
It appears that the Greater Himalaya rocks were, indeed, first pushed deep under Eurasia at Tibet by the northward push of India, and were heated up there.
But the India collision zone apparently then shifted south and shoved rocks under the Greater Himalaya rocks, lifting them up. Monsoon rains eroded away the surface, allowing the rocks to buoy skyward.
"There is a big controversy in the Himalaya right now," said Robinson. Western Nepal could hold more answers, and despite the hard working conditions, she's itching to get back to gather more data. But civil unrest is now keeping her out.
