An ash plume billows from the crater atop Mount St. Helens hours after its eruption began on May 18th, 1980, in Washington state. The column of ash and gas reached 15 miles into the atmosphere, depositing ash across a dozen states. #

On May 17, 1980, vulcanologist David Johnston sits at Coldwater II camp near Mt. St. Helens. At 8:32 a.m. the next morning, Johnston radioed a message to the USGS headquarters: "Vancouver, Vancouver, this is it!" Johnston did not survive the eruption. Coldwater II was later re-named "Johnston Ridge" in honor of Johnston. #

An animated series of images showing the May 18, 1980, eruption of Mt. St. Helens. Clearly visible in the first few images is the largest recorded landslide in history—the entire north face of the volcano sliding away following a shallow earthquake. The newly-exposed core of the volcano then erupted. #

Ash clouds from Mount St. Helens move over Ephrata airport in Washington on Monday, May 19, 1980. Communities across central and eastern Washington were covered in 3-5 inches of gritty, fine, ash particles. #

A house is submerged along the Toutle River which flooded in the aftermath of the eruption of Mount St. Helens on May 19, 1980. Area streams and rivers rose quickly as ice and snow on the volcano melted instantly. #

A logging operation along the Toutle River, Washington, about 20 miles from Mount St. Helens, in ruins after flooding from ice and snow melt from the mountain, in May of 1980. #

Bob Brown, left, and his brother John attempt to lead three horses to safety out of the Weyerhaeuser 19 Mile camp in Kid Valley, Washington. The yard was flooded by the Toutle River following the eruption of Mount St. Helens. #

Bob Brown (right) and John Brown climb onto railroad car, heading down the train along with two additional would-be horse rescuers, giving up their efforts as they flee for their lives as flood waters from the Toutle River begin a sudden rise on May 19, 1980. All four people reached safety but the horses are presumed to have drowned. #

The crater left at the summit of Mt. St. Helens, after it lost more than 1,300 feet of elevation to the catastrophic landslide and eruption of May 18, 1980, the surrounding landscape still steaming. #

The streets of Yakima, Washington, are dark at 3:00 p.m. after an eruption of Mount St. Helens on May 18, 1980. Volcanic ash covered the streets as people wore masks to avoid breathing the particles. #

Fifteen-year-old Heidi Havens gives Allen Troup, 16, a kiss as he prepares to board a Spokane City bus, on May 27, 1980. Spokane residents had to wear face masks while outside for days after the eruption because of possible health threats from volcanic ash sprayed over the area by Mount St. Helens on May 18. #

The slopes of Smith Creek valley, east of Mount St. Helens, show trees blown down by the May 18, 1980 lateral blast. Two U.S. Geological Survey scientists (lower right) give scale. The direction of the blast—shown here from left to right—is apparent in the alignment of the downed trees. Over four billion board feet of usable timber, enough to build 150,000 homes, was damaged or destroyed. #

A Washington state geologist and a reporter walk toward the crater of Mount St. Helens in May of 1981, almost a year after the volcano exploded, causing dramatic destruction for miles around. They were near the steaming lava dome with the snow-covered crater wall beyond. #

Satellites in orbit and scientists on the ground still monitor the mountain and track the recovery of Mt. St. Helens. This image shows a three-dimensional view of the mountain, looking toward the southeast, as it appeared on April 30, 2015. The image was assembled from data acquired by the Operational Land Imager on Landsat 8 and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on Terra. #