How many Tunguska incidents have occured ..we just haven't located the signs left afterward.
A Documentary was aired last week with a team entering the Brazilian rain forest to find a multiple impact site.
A sizeable Tunguska event was discovered recently in Australia...the surrounding desert scooped out like a kids sand box.
[You may have read this info allready]
November 26,1997 Web posted at: 5:39 p.m. EST (2239 GMT) SYDNEY, Australia (AP) -- An asteroid that tumbled through space for eons blasted into the sea off Antarctica more than 2 million years ago with the force of "a cosmic bomb," a multinational team of scientists said in a research paper published Wednesday. Striking the Bellingshausen Sea with the explosive power of 100 billion tons of TNT, the asteroid Eltanin blew a column of water 5 kilometers (3 miles) high and punched a temporary "oceanic crater" in the sea, according to the paper, which appeared in the British science journal Nature. The researchers estimate the asteroid was at least 1 kilometer (six-tenths of a mile) and possibly up to 4 kilometers (2.5 miles) in diameter. The blast in the ocean did not leave a crater on the seabed, but a similar strike on land would have left a hole 15 to 40 kilometers (9 to 25 miles) across. 'Devastating mega-tsunamis' Eltanin, the only asteroid ever known to have hit water, triggered waves 20 to 40 meters (65 to 130 feet) high, "devastating mega-tsunamis" that swamped the coasts of South America and Antarctica. "The tsunami ... destroys enormous, large areas. ... In the Pacific Rim there are signs of such things," one of the lead researchers, Rainer Gersonde of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, told The Associated Press in a telephone interview Wednesday. Sediment spread up to 4,000 kilometers (2,500 miles) away and dust, vapor and salts wafted around the world. Enough debris and hot vapors were emitted to possibly damage the Earth's ozone layer, the researchers said. "The dust and vapor probably caused a major change in climate, but whether that persisted or was for just a few years, we just don't know," said Karsten Gohl, a geologist from Macquarie University in Sydney who worked on the project. There is no evidence that the climatic change caused the extinction of any species. New seismic and deep-sea surveys conducted in 1995 by the German research ship Polarstem enabled the scientists to accurately date the blast to the late Pliocene period, 2.15 million years ago, and to gauge its effects. An enigma solved? The blast was well after the Northern Hemisphere's Ice Age began but "close to one of the strongest cooling events in this time period," the researchers'paper said. "It might be that this strong cooling was related to the impact," Gersonde told AP. The fallout from the blast may explain the "Sirius enigma," the puzzle of why marine fossils are found high above sea level in the Transantarctic Mountains. The researchers believe fallout from the stearn and vapor cloud dropped micro-fossils directly on the mountains, an idea that geologist Peter Barrett at Victoria University of Wellington, New Zealand, called "reasonably plausible." David Harwood at the University of Nebraska, an expert on the Sirius fossils, conceded that the fallout theory "has potential" but said some Sirius deposits do not fit the model. He is among those who feel moving ice sheets may have scoured fossil deposits and redeposited them in unexpected sites. The Eltanin impact was a medium blast, as asteroids go. About 65 million years ago, an asteroid about IO kilometers (6 miles) in diameter struck off Mexico's Yucatan Peninsula and is widely believed to have killed off the dinosaurs by blotting out the sun with the dust it kicked up. But rocks far smaller than Eltanin can cause massive damage: A meteorite only 45 meters (150 feet) across created Arizona's Meteor Crater, 1,220 meters (4,000 feet) across and 180 meters (600 feet) deep. First known ocean strike Eltanin is the only asteroid known to have struck the ocean, compared with about 140 known to have hit land -- even though the Earth's surface is 70 percent water, Jan Smits of the Research School of Sedimentary Geology at Amsterdams Vrije University noted in a commentary on the research in Nature. Besides Gersonde, in Germany, researchers on the project included Frank Kyte at the Institute of Geophysics and Planetary Physics at UCLA and scientists from the Department of Geology at the University of Salamanca in Spain; Macquarie University's School of Earth Sciences in Sydney; and the U.S. Naval Research Lab in Washington. Eltanin is named for the U.S. research ship that brought up deep sea samples in 1965 that later were formed to contain iridium, an element in asteroids.
