Mount St. Helens looks serene in a photograph taken from the shores of Spirit Lake in Washington State in 1973—a few years before the volcano's infamous 1980 eruption.
Today marks the 30th anniversary of the blast, which killed 57 people and leveled hundreds of square miles of pristine old-growth forest.
"The eruption really caused drastic changes in the forest ecosystem," said Mark Swanson, a forest ecologist at Washington State University.
Before the eruption, the dense forest cover meant there was little light and low wind speeds in the area. But afterward, Swanson said, "you had a very open system ... with a layer of volcanic ash over most of it, varying in depth from hundreds of meters to just a few inches."
A steam plume rises from the gaping maw of Mount St. Helens two years after its May 1980 eruption.
The blast was so powerful that it destroyed the top 1,300 feet (400 meters) of the volcano, leaving a crater 2 miles (3.2 kilometers) wide.
Some of the first colonizers of the bleak, post-blast mountain were insects blown in from afar—although some died instantly in the baked landscape, said University of Washington professor emeritus John S. Edwards.
Before the blast, the volcano's icy peak rose more than 5,000 feet (1,500 meters) above its base, which was surrounded by forests dominated by tall fir trees.
When the volcano erupted in May 1980, much of the surrounding forest was engulfed by pyroclastic flows—superhot clouds of ash, rocks, lava, and gases that hurtled down the volcano's flanks at speeds of up to 500 miles (800 kilometers) an hour, Washington State's Swanson said.
The heat and speed of the pyroclastic flows killed a lot of trees, he added.
Image courtesy NASA/USGS
Mount St. Helens Aerial, 1983
Forests on the north face of Mount St. Helens still appear as gray ash fields a few years after the eruption, as seen in a 1983 Landsat picture.
The barren landscape provided new opportunities for some new tree species. Pre-eruption forests around Mount St. Helens were mostly made of Douglas firs. But the current forest cover is heavily populated by trees such as red alder and willow, which have light seeds that disperse easily in the wind.
Many of the first trees to recolonize the volcano after the blast were reliant on the corpses of dead insects for nutrients such as nitrogen and phosphorous, the University of Washington's Edwards said.
"The bug bits tended to get blown into microcrevices in the landscape, which is where seeds blow," he said. "So in a very rudimentary way, the seeds germinated in bug compost."
Image courtesy NASA/USGS
Mount St. Helens Aerial, 2000
By 2000 the charred landscape around Mount St. Helens was showing signs of healing, as seen from a Landsat satellite.
The view from roughly the same angle in 1982 shows the obliterated north face of Mount St. Helens sitting in contrast to Mount Hood's snowy peak.
Magma rising into the volcano from Earth's interior triggered the earthquakes, which ultimately caused Mount St. Helens to erupt, said University of Washington professor emeritus Steve Malone.
The May 18 eruption was more powerful on the north side, because earthquake-triggered avalanches in the weeks leading up to the blast had weakened that part of the volcano's structural integrity.
"Earthquakes were banging away at it at a fairly regular rate," Malone said. "One more was just enough, until finally [the volcano's surface was] weak enough that it just let loose."
Photograph courtesy Robert Krimmel, USGS
The Day Before
Mount St. Helens rises above the surrounding old-growth forests in a photograph taken from Johnston's Ridge, six miles (ten kilometers) northwest of the volcano, a day before the 1980 eruption.
Snowbanks that had accumulated along the volcano's slopes before the eruption offered an unexpected refuge for some of the shorter trees and plants that normally form the understory of forests, Washington State's Swanson said.
"So you had herbs and shrubs and shade-tolerant trees that were protected from the force and the heat of the blast," Swanson said. "In some areas, you had a ready-made forest community that could spring right up" after the blast.
Photograph courtesy Harry Glicken, USGS
Another photograph taken from Johnston's Ridge in September 1980 shows the largely barren landscape surrounding Mount St. Helens's crater.
Malone, the retired director of the University of Washington's Pacific Northwest Seismic Network, called the 1980 Mount St. Helens blast a "baptism by fire" for him and his colleagues.
"Here in the Pacific Northwest we had little experience with volcanoes in our backyard," he said.
"We had to transition very quickly from being a pure research institute to one whose work had real value to public safety." (Read a first-hand account of the eruption published in the January 1981 issue of National Geographic magazine.)