How do the working crews stop the large chunk of mountain from crashing into Heimaey's town and port?

Thorbjorn Sigurgeirsson decides that the best approach to stop the moving mountain that broke off the volcano before it reaches the town and port is to block it with a natural barrier of cooled lava. The work crews then pump seawater into a section of lava directly on the path of the mountain. The moving mountain crashes into the cooled lava and and breaks up into smaller, non-moving pieces.