In Dante's Peak(1997), Harry (Volcanologist) went into a town next to Mammoth hill (a volcano) and took up a job in monitoring the volcano itself.
After a while, Harry believed the volcano was going to erupt after a few false alarm and he warned a few surounding towns around it...but it didn't erupt.
The next time it showed signs, Sulphur Dioxide had gotten into the main water source. Not long after he was investigating, the volcano erupted...sending the town into a frenzy.
What I want to know is:
If Harry knew the volcano was about to erupt...why didn't he get the evidence and evacuate the town immediately instead of leaving it and studying it?