The 1980 Mount St. Helens eruption was one of the most significant natural disasters in the US in the past half-century. Landsat captured the extent of and recovery from the destruction. (Credit: NASA's Goddard Space Flight Center/NASA's Earth Observatory)
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This video is public domain and can be downloaded at: http://svs.gsfc.nasa.gov/goto?10550Most of the geologic processes that shape our planet, such as the creeping movement of tectonic plates, are often too slow to see on human timescales, but every so often, geology produces a moment with in-your-face intensity.
The explosive eruption of Mount St. Helens in Washington State on May 18, 1980, was such a moment. Situated on a subduction zone where the Juan de Fuca Plate in the Pacific descends under the North American Plate, Mount St. Helens is one of a number of Cascade Range volcanoes that stretch from British Columbia to northern California. The peak is the most active volcano of the group, sitting over an area where the Earth's surface holds in the melted solid rock.
Landsats 2, 3, 5 and 7 captured the Mount St. Helens eruption and subsequent recovery of its surrounding ecosystem over the last 32 years. The scenes collected by Landsat 2 and 3 from 1980 to 1983 show vegetation in red. Natural color images appear with the launch of the new Thermal Mapper instrument on Landsat 5 in 1984 and continued with Landsat 7.
The first three seconds of the visualization depict the condition of the volcano prior to the morning of May 18. It has a conical, glacier-clad peak like the others in the Cascades chain and had been inactive since the mid-nineteenth century. Scientists began actively monitoring Mount St. Helens in March 1980 when the volcano "reawakened" with a 4.2-magnitude earthquake and started venting steam.
On the morning of the now-historic eruption, a 5.2-magnitude earthquake triggered the sequence of events that would be life altering to many in the area. A massive slab of the northern slope of Mount St. Helens collapsed and roared over the landscape in an enormous debris avalanche—the largest in recorded history. With a gigantic hole ripped down the volcano’s side, superheated gases and rock fragments exploded laterally instead of vertically—something that had not been witnessed and recorded before in modern times.
The blast raged with wind speeds reaching 200 to 250 miles per hour (320 to 400 kilometers per hour) at temperatures of 680˚F (360˚C), flattening and scorching trees. For more than nine hours after the lateral blast, Mount St. Helens gushed an ash plume that reached 15 miles high into the atmosphere, and in 15 days, circled the globe. Deadly pyroclastic flows, at least 1,300˚F (704˚C), spewed from the crater and covered 6 square miles (15 square kilometers) under feet of choking pumice.