Intraglacial volcanoes of the Laugarvatn region, south-west Iceland—I

The shape and structure of a group of basaltic volcanoes is described. It is concluded that these volcanoes grew within bodies of melt-water in an ice-sheet. The activity of some was limited to effusion in water, resulting in steep-sided piles of pillow lava. In others which mounted to a water surface activity culminated in explosions which mantled the pillow lava pile with vitric tuff. With still others explosive emergence was superseded by quiet effusion of lava in air. Flows advanced outwards into an encircling lake on deltas of breccia formed at their fronts, mantling and obscuring the products of the earlier phases of aquatic effusion and explosive emergence. Details of the structure and structural interrelationships of the volcanoes are explained in terms of eruptions within an ice-sheet of continually increasing thickness. Attention is drawn to the morphological contrast between intraglacial and extraglacial basaltic volcanoes.