And today there is a head of steam to vent.

ECONOMIST: Iran and the world

We pass a white wall of mountains off to the left and, on the right, an active volcano with steam curling out of the vent.

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In this configuration, the HTP is passed over a catalyst pack to decompose it into steam and oxygen, but instead of igniting a fuel grain, this superhot gas is allowed simply to vent through the chamber nozzle.

BBC: Science & Environment