When a volcano erupts beneath a glacier, it creates a pool of melted water that can extend to the glacier's surface, forming a lake. After the glacier is gone and the volcano is exposed, we can look at the shape, rock type, and elevation of the volcano to determine how thick the ice was during eruption. We investigated two neighbouring subglacial volcanoes in Iceland, which erupted during the last ice age and are now no longer covered in ice. We observed that the larger structure has rock types, textures, and elevation suggesting that it erupted beneath a glacier that was at least 350-400 m thick. The smaller, adjacent structure's morphology and rock types imply that the glacier it erupted beneath was 100 m thick. We propose that the glacier covering these two volcanoes during their eruptions was thicker or thinner at different times, and we will use our samples and field observations to help figure out the glacial thickness over time.