In the Deadly Shadow of Vesuvius

You chose answer 3.

Bad news, because the plug's presence indicates that the next eruption is likely to be effusive-producing scorching, deadly rivers of lava—rather than a relatively harmless pyroclastic flow.

Right answer, wrong explanation. A volcano with an "unplugged" conduit is more likely to produce an effusive eruption—a relatively gentle process marked by the flow of lava down the mountainside. (The lava, though red-hot, moves slowly, usually only up to 10 miles per hour or so, so it is relatively easy to avoid. Such eruptions are common in Hawaii. You may have seen footage of them on TV.) Pyroclastic flows, however, are another story altogether - but before we give away the whole answer...

Give it another try.