Mercury swamp

Mercury swamps were located on the planet Vulcan. They contained rocks and pools of mercury that occasionally sprayed liquid mercury.

At one point in Vulcan's history, a Dalek spaceship crashed in the mercury swamps. Hundreds of years later, colonists found the ship in the swamps. The Second Doctor, Ben and Polly landed in the swamps and explored. The Doctor found a body in the swamps. Ben and Polly were overcome by mercury fumes and rescued by the colonists. (DW: The Power of the Daleks)