By clearing the way for flowing rock that one geologist compares to melted Brie, rain may have made possible the Himalaya's most intense growth period, a new study suggests.
The 50-million-year-old collision of the Indian and Eurasian tectonic plates, which continues today, created the world's tallest mountains (map of Earth's tectonic plates).
But a new study of ocean sediments found that a period of increasing monsoon intensity coincided with a great Himalayan growth spurt, between about 23 million and 10 million years ago.
Until recently, it was presumed that the rising of the Himalaya had intensified East Asian monsoons, which blow warm, wet, Indian Ocean clouds toward the mountains. As the clouds "climb" the mountains, they drop enormous quantities of rain on the foothills.
In a surprise twist, the new findings hint that the millions of years of strengthening monsoons may have in fact encouraged the Himalaya's rapid rise.
The result would have been a sort of feedback loop, with the growing Himalaya encouraging stronger storms, the stronger storms encouraging the Himalaya to rise higher, which would further strengthen the storms, and so on.
(Related: "Chinese Kingdoms Rose, Fell With Monsoons?" [November 6, 2008].)
Brie-Cheese Geology
"It's kind of a complicated story," said study co-author Kip Hodges, an Arizona State University geologist who studies continental tectonics.
Hodges compares the geology of the region to a piece of Brie cheese.
The crust of the cheese is the rocky surface of the high Tibetan Plateau, north of the Himalaya (photos of the Himalaya).
Beneath it however, is a layer of rock that's more like soft cheese, capable of flowing under pressure or when heated.
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