The possibility of lava flows cutting off the harbour was the most significant threat facing the town. One contingency plan devised, should the harbour be closed off, was to cut through a low sand spit on the north side of the island to provide a new channel into the harbour, but it was hoped that if the lava flow could be slowed, this would not be necessary. Lava flows had been sprayed with water in attempts to slow them in Hawaii and on Mount Etna, but these had been rather small-scale operations with limited success. However, Professor Þorbjörn Sigurgeirsson carried out an experiment that proved that further advances of the lava could be impeded by prematurely solidifying the advancing lava-flow front.