Physics of Cooling Lava

On January 23rd 1973 a new volcano unexpectedly erupted in the Vestmannaeyjar archipelago, southwest of Iceland. The new volcano was a fissure 1.25 miles long and only 1100 yards from the center of town, also named Vestmannaeyjar. The new volcano was named Heimaey. The town was mostly evacuated over the next few days and the lava slowly flowed towards town and the mouth of the harbor for the next seven months. Vestmannaeyjar is the only good harbour in that part of Iceland, and was the base for a large fishing fleet that produces a significant part of Iceland’s GNP. As the lava threatened to overrun the town and close off the harbor, a decision was made to try to slow and divert the lava by cooling it with sea water. The idea was initially scoffed at, but when small initial efforts seemed to have an effect the scale of the operation was increased. Over seven months eight million cubic yards of sea water were pumped onto the lava flow; they cooled 5 million cubic yards of basalt lava to solid rock. The harbor and much of the town survived the eruption, likely as a result of the efforts to cool the lava.

Iceland is known for its volcanic activity. A few years before Heimaey erupted; a nearby sub oceanic eruption formed the new island of Surtsey. The town of Vestmannaeyjar already had an extinct volcano on its outskirts, the volcano was known as Helgafell. It was thought to have been extinct for several hundred years. In January 1973 a new fissure opened up a few hundred yards from the extinct volcano. It went clear across the island and into the ocean on both sides. Boats escaping the harbor saw red magma under the water, and sub oceanic power and water lines from the mainland were broken by the eruption. In the initial eruption a curtain of lava 500 feet erupted from the fissure, after a few days the eruption was mostly from a single vent, with a cinder cone 300 feet tall. The lava flows from the eruption were a viscous slow moving basaltic magma. Average speeds