The seconed type of volcano-ice interaction is located only to the east, south and southwest of the Tanzilla Plateau, in the Cassiar Mountains, Skeena Mountains and in the Boundary Ranges. Volcanic activity in these locations is also largely mafic in composition, but the extensive elevations of these areas had a much more impressive influence on glaciation and subglacial volcanism. High altitude glaciation took over when the Cordilleran Ice Sheet was not present and even when buried by the Cordilleran Ice Sheet, basal ice movement was strongly influenced by the deep, pre-glacial drainages. Accordingly, the erosional remnants of subglacial volcanoes are minor and intermittent. In the Skeena Mountains, separated outcrops of pillow lava and volcanic breccia are generally found side by side on the summits of sharp rugged mountain ridges, with presumably temporally-associated pyroclastic rocks having collected downslope.