sand avalanche

sand avalanche

[′sand ‚av·ə‚lanch]
(geology)
Movement of large masses of sand down a dune face when the angle of repose is exceeded or when the dune is disturbed.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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As the (http://www.nytimes.com/2000/05/19/arts/presenting-a-fight-to-the-death-from-80000000-bc.html?mcubz=1) New York Times describes it, the velociraptor had a claw of its foot in the neck of the protoceratops and was gripping its head, while the prey was biting the velociraptor's arm, when a sand avalanche came rushing down on top of them.
"I once started a sand avalanche at the top of a dune, and the conditions were just right--it was like melted chocolate flowing down a hill in slow motion," says Woolsey.
Captain Ali Al Qusaib who managed the rescue said that the rescue attempt was difficult despite the tricky nature of sand avalanches. The workers were in difficult positions and the size of the hole which kept on collapsing during the rescue had to be held by wooden planks.
After storms patches of dark sand are often visible on contemporary dune surfaces and have been observed in places where sand avalanches are unlikely or impossible.
The sound originates when sand avalanches down the lee face of a dune, explains Hunt.
One towering dune emits a loud thrumming roar as we set small sand avalanches in motion by sliding down the dune on our backsides, or driving down it in the 4x4 at an impossible angle.
Called "booming" or "singing," the rumbling sound is emitted as sand avalanches on the steeper, leeward side of the dunes.