English: An ash-laden eruption column rises above a volcanic cone behind the town of Vestmannaeyjar on the island of Heimaey in 1973. The pumping operation in the foreground was designed to cool the front of an advancing lava flow that threatened the town and its harbor. Twenty-two postglacial eruption sites are known in the mostly submarine Vestmannaeyjar volcanic system, which occupies a shallow shelf off the southern coast of Iceland. It contains the renowned island of Surtsey, which grew from the sea floor in an eruption that began in 1963. Photo by Jack Lockwood, 1973 (U.S. Geological Survey).