In all, eruption of Mount St. Helens released an amount of energy equivalent to 27,000 Hiroshima-sized nuclear weapons and ejected more than 1 cubic mile (4 km³) of material. Without warning, at 8:32 a.m., one of the largest landslides in recorded history traveled at 110 to 155 miles per hour and moved 13 miles down the North Fork Toutle River, filling its valley up to 600 feet deep with avalanche debris. An area of about 24 square miles was covered.
Ironically, Johnston was the only geologist to correctly predict the nature of the eruption. The official USGS prediction was that the volcano would experience a conventional vertical column eruption, while Johnston had proposed that the blast would be lateral and originate from the bulge which he had observed developing on the side of the mountain. But, finally, he just committed a single mistake: he considered that an observation post about 6 miles from the volcano was relatively safe.
* On the top of the post, David A. Johnston, 13 1/2 hours before he was killed in the 1980 eruption of Mount St. Helens.
More info and sources: 1, 2, 3
10 agosto 2007
David Alexander Johnston was a volcanologist with the United States Geological Survey (USGS). Johnston was manning an observation post about 10 km (6 miles) from the volcano Mount St. Helens on the morning of May 18, 1980. He was the first to report the eruption, transmitting the famous message "Vancouver! Vancouver! This is it!" before being swept away by the lateral blast created by the collapse of the mountain's north face. His body was never recovered.