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Mount St. Helens - Wikipedia, the free encyclopedia

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From December 7, 1989 to January 6, 1990, and from No

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Cascade Range, Mount St. Helens is a large eruptive cone consisting of lava

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map #26 USGS Mount St. Helens
Type #21 Active stratovolcano
Volcanic   arc / belt Cascade Volcanic Arc
Age of rock < #20 40,000 yrs
Last eruption #19 2004–2008 (ongoing)
First ascent #18 1853 by Thomas J. Dryer
Easiest route #17 Hike via south slope of volcano (closest area near eruption site)

#1 Mount St. Helens is an active stratovolcano located in Skamania County , Washington , in the Pacific Northwest region of the United States . #2 It is 96 miles (154   km) south of Seattle and 53 miles (85   km) northeast of Portland, Oregon . #12 Mount St. Helens takes its English name from the British diplomat Lord St Helens , a friend of explorer George Vancouver who made a survey of the area in the late 18th century. #3 The mountain is located in the Cascade Range and is part of the Cascade Volcanic Arc , a segment of the Pacific Ring of Fire that includes over 160 active volcanoes . #10 This volcano is well known for its ash explosions and pyroclastic flows .

#4 Mount St. Helens is most famous for its

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USGS Mount St. Helens

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St. Helens catastrophically erupted on May 18, 1980. After many months of lead-up activity, including the growth of a huge bulge on the north part of the mountain, a moderate earthquake caused the entire north flank of the mountain to slide away in the largest landslide in recorded history

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The newly exposed hot and pressurized rock in the volcano responded by producing the largest historic volcanic eruption in the 48 contiguous U.S. states.[30] (See the Geology section for more detail.)

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U.S. President Jimmy Carter surveyed the damage and said, "Someone said this area looked like a moonscape. But the moon looks more like a golf course compared to what's up there."[32] A film crew, led by Seattle filmmaker Otto Seiber, was dropped by helicopter on St. Helens on May 23 to document the destruction. Their compasses, however, spun in circles and they quickly became lost. A second eruption occurred on May 25, but the crew survived and was rescued two days later by National Guard helicopter pilots

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On March 20, 1980, Mount St. Helens experienced a magnitude

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On March 20, 1980, Mount St. Helens experienced a magnitude 4.2 earthquake

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The collapse of the northern flank of St. Helens mixed with ice, snow, and water to create lahars (volcanic mudflows). The lahars flowed many miles down the Toutle and Cowlitz Rivers, destroying bridges and lumber camps. A total of 3,900,000 cubic yards (3,000,000 m3) of material was transported 17 miles (27 km) south into the Columbia River by the mudflows.[43]

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For more than nine hours, a vigorous plume of ash erupted, eventually reaching 12 to 16 miles (20 to 27 km) above sea level.[44] The plume moved eastward at an average speed of 60 miles per hour (100 km/h) with ash reaching Idaho by noon. Ashes from the eruption were found collecting on top of cars and roofs next morning, as far as the city of Edmonton in Alberta, Canada

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nd from

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From December 7, 1989 to January 6, 1990, and from No

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field,

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