The eruption of Mount St. Helens in Washington State on May 18, 1980, is certain to be remembered as one of the most significant geologic events in the United States of the 20th century. The explosion, on May 18, was initiated by an earthquake and rockslide involving one-half cubic mile of rock. As the summit and north slope slid off the volcano that morning, pressure was released inside the volcano - where super hot liquid water immediately flashed to steam. The northward-directed steam explosion released energy equivalent to 20 million tons of TNT, which toppled 150 square miles of forest in six minutes. In Spirit lake, north of the volcano, an enormous water wave, initiated by one-eighth cubic mile of rockslide debris, stripped trees from slopes as high as 850 feet above the pre-eruption water level. The total energy output, on May 18, was equivalent to 400 million tons of TNT - approximately 20,000 Hiroshima-size atomic bombs.
Mudflows, from Mount St. Helens, were responsible for the most significant erosion. A mudflow on March 19, 1982, eroded a canyon system up to 140 feet deep in the headwaters of the North Fork of the Toutle River Valley, establishing the new dendritic pattern of drainage. As ICR scientists surveyed this new terrain, they began to contemplate the processes which may have formed the Grand Canyon of the Colorado River. The little “Grand Canyon of the Toutle River” is a one-fortieth scale model of the real Grand Canyon. The small creeks which flow through the headwaters of the Toutle River today might seem, by present appearances, to have carved these canyons very slowly over a long time period, except for the fact that the erosion was observed to have occurred rapidly! Geologists should learn that, since the long-time scale they have been trained to assign to landform development would lead to obvious error on Mount St. Helens, it also may be useless or misleading elsewhere.