The subdued relief on the Tanzilla Plateau strongly influenced edifice morphologies, favoring broad-based tuyas. The hydrological conditions in these areas likely were controlled by relatively uniform ice thickness and gentle topography. 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. The third type of volcano-ice interaction is geographically restricted to three volcanoes, including Level Mountain, the Mount Edziza volcanic complex and Hoodoo Mountain. All three volcanoes are broad enough to hold ice caps that likely altered regional ice flow while still being altered by the Cordilleran Ice Sheet at individual periods. The Mount Edziza and Level Mountain complexes have shelves of older lava with elevations more than and have been zones of volcanic activity long enough that their geothermal activities might have had effects on movements of the Cordilleran Ice Sheet much like the Grímsvötn caldera in Iceland, which has been a significant heat source beneath the vast Vatnajökull icecap. At the Edziza complex, most of the subglacial products were formed on top of the main lava plateau, which now rises at least in elevation above adjacent stream valleys. The Edziza complex consists of a collection of mafic subglacial products, but more unusually, including Hoodoo Mountain and Level Mountain, comprises some of the largest deposits of peralkaline felsic subglacial volcanics known. At the Edziza and Level Mountain complexes, glacier hydrology of the Cordilleran Ice Sheet was possibly dominated by a complicated interaction between drainage on the flat plateaus under relatively thinner ice and drainage within nearby steep valleys filled with much thicker ice.