I am pretty sure that last photo showed the people inside the volcano and not on the sides.
During the St Helen’s eruption and pyro-clastic flow it is estimated that the velocities where 670 miles an hour or greater. It could have been supersonic. At Johnson ridge some miles from the volcano I have seen pine trees two and three feet in diameter broken off a foot or two above the ground. The tree itself was no where near. It was just gone.
At Johnson Ridge now is a great site for the public complete with Geologic exhibits and video displays explaining what happened. It is well worth the nominal price to see.
It is called Johnson Ridge in memory of a geologist that was studying the potential eruption of Mount St. Helens. When St. Helens erupted he reported. He was miles away and thought safe. The side of the volcano blew out directly at him. When the pyroclastic flow headed his way he knew he was a dead man. His body was never found. In all probability it was totally incinerated. He was hit by wind and volcanic debris and great temperature at velocities of several hundred miles an hour. It was quick.
Johnson Ridge is an appropriate name for this site.