After reaching its maximum extent the Cheekye Glacier along with part of the area's ice sheet were covered with volcanic ash and fragmented debris from Garibaldi. This period of growth began with the eruption of the Atwell Peak plug dome from a ridge surrounded by the several thousand foot ice sheet. As the plug dome rose, massive sheets of broken lava crumbled as talus down its sides. Numerous Peléan pyroclastic flows (consisting of a super-heated mix of gas, ash, and pumice) accompanied these cooler avalanches, forming a fragmental cone in volume and an overall slope of 12 to 15 degrees. (Erosion has since steepened this slope.) Some of the glacial ice was melted by the eruptions, forming a small lake against Brohm Ridge's southern arm. The volcanic sandstones seen today atop Brohm Ridge were created by ash settling in this lake.