Environment – Where eruption occurs is important. Subaerial lava flowing on land cools slower than… Submarine lava which is quickly quenched.
Eruptions to Remember Mt. St. Helens – Erupted May 18, 1980, 8:32 A.M. Earthquake triggered landslide released pressure. Initial vertical blast followed by a much stronger lateral blast that tore off the entire north side. 396 m was blasted away.
Eruptions to Remember Mt. St. Helens – Erupted May 18, 1980, 8:32 P.M. The blast devastated 600 km 2 and killed 61 people. Lahars plugged the Toutle River; closed the Columbia. Ash fell in North Dakota; highways and rail lines stopped. Destroyed timber valued at several 100 million dollars.
Famous for telling reporters that being on the mountain was like "standing next to a dynamite keg and the fuse is lit",  Johnston had been among the first volcanologists at the volcano when eruptive signs appeared, and shortly after was named the head of volcanic gas monitoring. Though a careful analyst, Johnston strongly believed that scientists needed to take this risk for themselves in order to prevent civilian deaths, and therefore chose to partake in dangerous on-site monitoring. He and several other volcanologists prevented people from being near the volcano during the few months of pre-eruptive activity, and successfully fought pressure to re-open the area.  Their work kept the death toll at a few tens of individuals, instead of the thousands who possibly could have died had the region not been closed off. Johnston supported the lateral blast theory: he believed the explosive eruption would be ejected sideways out of the volcano, not upward. He also believed that the eruption would originate from the bulge. Because of this, he was more aware than most of the threat of a north-directed eruption USGS Geologist David Johnston