On May 18, 1980 Mount St. Helens erupted, becoming the first major volcanic eruption in the States since 1915. Keith Stoffel was attending the Yakima Gem and Mineral Show as a representative of the Division of Geology and Earth Resources for the Washington Department of Natural Resources (WA DNR). He and his wife Dorothy charted a plane that day with pilot Bruce Judson, unknowing of what was to come. From their vantage point they watched the volcano erupt, narrowly escaping thanks to the efforts of Judson. They captured a few photographs (including the one above) and Keith later summarized what he saw in a WA DNR paper (PDF):
Within a matter of seconds, perhaps 15 seconds, the whole north side of the summit crater began to move instantaneously. As we were looking directly down on the summit crater, everything north of a line drawn east-west across the northern side of the summit crater began to move as one gigantic mass. The nature of movement was eerie, like nothing we had ever seen before. The entire mass began to ripple and churn up, without moving laterally. Then the entire north side of the summit began sliding to the north along a deep-seated slide plane. I was amazed and excited with the realization that we were watching this landslide of unbelievable proportions slide down the north side of the mountain toward Spirit Lake. We took pictures of this slide sequence occurring, but before we could snap off more than a few pictures, a huge explosion blasted out of the detachment plane. We neither felt nor heard a thing, even though we were just east of the summit at this time. Dorothy saw the southern portion of the summit crater begin to crumble and slide to the north just after the initial explosion.
From our viewpoint, the initial cloud appeared to mushroom laterally to the north and plunge down. Within seconds, the cloud had mushroomed enough to obscure our view. At about this time, the realization of the enormous size of the eruption hit us, and we focused our attention on getting out of there.
They were not the only plane in the sky that day. A private plane flown by a former fighter pilot had been divereted to Seattle with his family, on return from vacation. In no apparent danger, he flew near the eruption and captured these photographs. His Grandson recently shared them (r/pics), but doesn’t have all the details of the day at the present.