Climate change can grind down plate tectonics

Washington, Oct 16 : New evidence has emerged that, given enough time, climate change can even alter the course of plate tectonics, by grinding them down.

The march of plate tectonics had previously seemed impervious to water and air's fickle motions. No matter the weather, plates would grind past and crash into one another to build mountain ranges, or sink into the hot depths of the mantle.

But, according to Brendan Meade of Harvard University, the mighty Andes mountain range, the longest on Earth, might not be here today if it wasn't for a drastic shift in climate 14 million years ago.

Over 7,000 kilometers (4,350 miles) long, the Andes are the result of the dense Nazca plate moving eastward from the Pacific Ocean and diving underneath the South American plate.

The collision creates nonstop earthquakes, volcanic eruptions and dramatic uplift that has thrust the Andes as high as the towering summit of Aconcagua, 6,962 meters (22,841 feet) above sea level.

Nothing outside of Asia is taller.

But, the mountains are young. Until 15 million years ago the Andes had never grown higher than 1,500 meters (5,000 feet). Then the climate changed.

"Back then, the Nazca and South American plates were converging at a rate of around 15 centimeters (six inches) per year," Meade said.

That is far faster than the rate at which the Indian and Eurasian plate are colliding to form the Himalayas today.

"But it was soaking wet. Then, all of a sudden, there was this aridification," said Meade.

Climate studies of the period show that the Andes region was a rainforest until 15 million years ago. Annual precipitation suddenly dropped from two meters (6.5 feet) to 20 millimeters (0.79 inches), reshaping the landscape into the parched desert it is today.

The lack of rain would have greatly reduced erosion, Meade and co-author Clinton Conrad of the University of Hawaii reason, allowing the young, humble Andes to rise to prominence.

As the mountains grew so did their weight, and the hefty range pushed down on the Nazca plate until friction slowed convergence to just seven centimeters (2.7 inches) per year, about half of what it was before the rains ceased.

"It's this amazing story - we're at the beginning of understanding how climate affects plate tectonics," Meade said.

On whether human-induced climate change could ever affect tectonics, she said, "It's a timescale question."

"Modern climate change has been going for tens to maybe hundreds of years. The change in climate would have to persist for hundreds of thousands of years at least, so the scale doesn't match up right now," she added.

ANI