This is another really good disaster movie. In this case a scientist thinks a volcano that is near a town is about to erupt and, as is so often the case, getting people to believe him is not an easy task. The movie shows some of the scientific work that goes on when a scientist is studying a volcano.
The movie shows how difficult it would be to evacuate even a relatively small town when news of an impending eruption gets out. The roadways would be clogged. Once the eruption starts, the sky fills with ash and this causes a helicopter to crash since it fouls up the helicopter's engines.
This is not a supervolcanic type of eruption, though, just one volcano erupting. The town gets pretty much destroyed by the pyroclastic flows from the volcano. This is ash and rock that flows down from the volcano; one way to think of it is it's a dry tsunami that is just as destructive and moves sixty miles an hour or more. It destroys most everything in its path.
Again, it's a very good movie.