fire water volcanoes empedocles maintained manifestation elemental fire plato contended channels hot cold waters flow inexhaustible quantities subterranean rivers depths earth snakes vast river fire ''pyriphlegethon'' feeds world 's volcanoes aristotle considered underground fire result thefriction wind plunges narrow passages wind played key role volcano explanations th century lucretius roman philosopher claimed etna completely hollow fires underground driven fierce wind circulating
Natural science Earth science Volcanology