Answer: Lack of water.
Journey to the Center of the World is a book published in 1864 by Jules Verne. It tells the story of three characters who reach the center of the Earth through an Icelandic volcano.
At some point in the story, as they are rushing through the volcano, the travellers take a wrong turn and they run out of water. Everyone is worried, and Axel almost dies, but Hans is able to tap into a subterranean river that they later rename "Hansbach."