Ancient Canyon Found Under a River in Tibet
A vast ancient canyon lies buried underneath a present-day river that cuts through the Himalayas in Tibet.
We think of canyons as being carved by rivers, as the Colorado River did with the Grand Canyon, so this item is a little mind-boggling.
In a just-published article in the journal Science, researchers from the California Institute of Technology have discovered an vast ancient canyon that lies buried underneath a present-day river that cuts through the Himalayas in Tibet.
The ancient canyon is thousands of feet deep in places, and apparently was carved by a previous river 3 to 7 million years ago.
"I was extremely surprised when my colleagues, Jing Liu-Zeng and Dirk Scherler, showed me the evidence for this canyon in southern Tibet," Caltech geology professor Jean-Philippe Avouac said in a press release "When I first saw the data, I said, 'Wow!' It was amazing to see that the river once cut quite deeply into the Tibetan Plateau because it does not today."
The ancient river "existed in this location prior to about 3 million years ago, but at that time, it was not affected by the Himalayas. However, as the Indian and Eurasian plates continued to collide and the mountain range pushed northward, it began impinging upon the river. Suddenly, about 2 1/2 million years ago, a rapidly uplifting section of the mountain range got in the river's way, damming it, and the canyon subsequently filled with sediment.
The scientists analyzed core samples collected by the China Earthquake Administration, which were taken from five locations along the Yarlung Tsangpo River. They found that at several locations there were sedimentary conglomerates, rounded gravel and larger rocks cemented together, that are associated with flowing rivers, until a depth of 800 meters or so, where the record clearly indicated bedrock. This indicated that the river once carved deeply into the plateau.
The discovery may force geologists to rethink long-held assumptions about how the Himalayas' dramatic gorges formed.
The Yarlung Tsangpo river in Tibet
In this roundup of recent imagery from around the world, an aurora is seen above Norway, disaster is narrowly averted at the World Trade Center, and an astronaut captures the Rio Grande from aboard the space station. The flow lobe (above) on Hawaii's Big Island destroyed a house on Monday and has also inflated significantly since then. The red roof in the background is the garage structure near the residence that caught fire.
An aurora is seen over the Lofot islands in Norway.
A girl puts flowers into a part of the former Berlin Wall during a memorial activity to commemorate the 25th anniversary of its fall.
The autumn has set in Kashmir where the leaves of gigantic Chinar trees turn first pale and then fiery red.
While flying over the border between Mexico and the United States, an astronaut aboard the International Space Station photographed these sister cities on the Rio Grande. The image shows the second largest metropolitan area (population 2.7 million) on the Mexico–U.S. border.
A scaffold carrying two workers hangs 69 floors up at One World Trade Center on Nov. 12, 2014 in New York City. Rescuers cut through glass to rescue the workers after their equipment malfunctioned.
Now in its third month, the fissure eruption at Iceland’s Holuhraun Lava Field has spread molten rock across 27 square miles (70 square kilometers), an area slightly larger than Manhattan Island.
In additional to having once been a favorite gemstone of the ancient Egyptians, olivine has another interesting quality: It can capture carbon. When left out in the open and combined with moisture under natural conditions, olivine absorbs carbon dioxide from the atmosphere and forms magnesium carbonate and silicic acid, which stores the carbon.