 It was once mistaken for a cinder cone and is now known to have erupted underneath about of glacial ice.The volcano erupted vigorously and cooled rapidly when the hot lava contacted the surrounding ice and melted it, creating an envelope of water around the rising volcano.The result was a cement-like surface with smoothed cobbles of granite, schist, phyllite and other non-volcanic pebbles which were carried by the ice from many kilometers distant.