<Tr> <Td> </Td> <Td> Sound of the eruption of Mount St. Helens, as heard from 140 miles away Amateur recording of a series of booms produced by the eruption, as heard from the town of Newport, Oregon (audio filtered and amplified). </Td> </Tr> <Tr> <Td_colspan="2"> Problems playing this file? See media help . </Td> </Tr> <P> Suddenly, at 8: 32 a.m., a magnitude 5.1 earthquake centered directly below the north slope triggered that part of the volcano to slide, approximately 7--20 seconds (about 10 seconds seems most reasonable) after the shock . The landslide, the largest in recorded history, travelled at 110 to 155 miles per hour (177 to 249 km / h) and moved across Spirit Lake's west arm . Part of it hit a 1,150 - foot - high (350 m) ridge about 6 miles (10 km) north . Some of the slide spilled over the ridge, but most of it moved 13 miles (21 km) down the North Fork Toutle River, filling its valley up to 600 feet (180 m) deep with avalanche debris . An area of about 24 square miles (62 km) was covered, and the total volume of the deposit was about 0.7 cubic miles (2.9 km). </P> <P> Scientists were able to reconstruct the motion of the landslide from a series of rapid photographs by Gary Rosenquist, who was camping 11 miles (18 km) away from the blast . Rosenquist, his party and his photographs survived because the blast was deflected by local topography 1 mile (1.6 km) short of his location . </P>

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