After it stopped and no additional material was being expelled, they do go back to look. Not recommended, but how often are big eruptions followed by even bigger eruptions?
Are you saying they should've run away from the park for the entire rest of the day or trip?
> how often are big eruptions followed by even bigger eruptions?
Quite often, I'd say.
Disruptions in the stability of geological processes frequently have a compounding domino effect... a volcanic eruption is often preceded by the opening of smaller vents, small landslides can trigger large landslides, small sinkholes can suddenly develop large ones, a trickle over a levee can turn into a total breach, most M>7.0 earthquakes have foreshocks...
You can't tell where the peak severity will be in a cluster of geological events except in hindsight after the entire cluster is passed.
There's no way to know if you're dealing with that until after the fact. A lot of the gawkers taking video ended up with serious injuries (not sure they all survived, some of those videos are quite close in retrospect)
Three simple facts here: 1) This is obviously abnormal enough for the people in the video to flee 2) the aftermath - (1:15+) - clearly demonstrates it was unsafe to be there and 3) there is no way to predict if the next eruption would be equally abnormal or worse unless one were trained in this field
There is no arguing those facts, it's 100% clear from that video you linked. Am I going to stay away from the park the rest of the day? I don't know, maybe. It really depends on the circumstances. I am not a volcanologist. I'm not even a scientist. I don't understand the specifics involved here. If it were me, and I can clearly see something abnormal happened, I would NOT risk going back unless I can somehow verify it was safe to do so. That's common sense. It might involve finding a park ranger to speak with or calling the ranger station to get more information. I've been to the geyser at Iceland where they have signs that explicitly tell you about the unpredictable nature of it and how people have been badly burned. This is not a no-risk situation, especially when the situation is not the norm.
I've been to the big island of Hawaii during volcanic activity and they explicitly tell you to stay away from it due to the gasses, rocks, lava, etc. Maybe that elevates my skepticism over the safety here, but it seems that's for good reason.
EDIT: here you go mate, you don't need to look at Hacker News comments. Take it from the Park itself:
Are you saying they should've run away from the park for the entire rest of the day or trip?
See @Saurik's sibling comment: https://news.ycombinator.com/item?id=41051381