"Vancouver! Vancouver! This is it!" These were the last words heard from David Johnson, a geologist stationed 10km from Mount Saint Helens, on the morning of May 18 1980. Johnson, who was monitoring the volcano, was radioing through to the Cascades Volcano Observatory in Vancouver, Washington, to alert them of an eruption. Moments later his observation post was buried in volcanic debris.
Mount St Helens erupted with a force 20,000 times that of the atom bomb that obliterated Hiroshima, or the equivalent of one atom bomb going off every second for eight hours. The blast burst through its northern flank and sent waves of volcanic rock, ash and gas crashing over the surrounding area, killing Johnson and 56 other people, about 7,000 big game animals, including elk, deer and bears, and several million fish from the nearby lakes.
The scenic Mount St Helens national park, a popular spot for outdoors activities, was scorched and blanketed in black and grey debris and now resembles a moonscape. In total, 570 sq km of land was flattened. The blast, as well as coming through the side of the volcano, sent ash soaring 25km into the stratosphere, turning day into night, and falling back to Earth in more than 11 different states - including Colorado and Minnesota - over an area of about 57,000 sq km.
One logger who was working in the surrounding forestland at the time of the eruption pointed out that had the blast not been on a Sunday, when most people were off work, the death toll would have been much higher. For the next six years the volcano recorded small, sporadic eruptions before falling silent. It reawakened in October 2004 with four explosions, sending ash 3,000m into the air. Lava continued to push slowly upwards until January last year, in what is known as a "passive eruption", forming a new dome at the top of the volcano.
Scientists play down the likelihood of another major eruption in the near future. "Mount St Helens is now in a rebuilding phase with relatively minor eruptions the most likely kind for the next several decades," said Steve Malone, a geophysicist at the University of Washington's department of earth and space sciences, who has been monitoring Mount St Helens for more than 30 years. "Indeed, some time again in the distant future it could erupt in a big way ? but this is likely a century or more away."