The mound turns out to be an island with an enormous geyser. But when standing on its top we see a more serious problem: An approaching violent storm!
If we stay on the island we could patch up our raft and then get back to the original shore, aided by the storm winds. But my uncle has a far more dangerous idea: head for the heart of the storm and use it to push us to the other side of the sea! Or, I think more likely, to our deaths! or could we do something else?