At least eight volcanic vents compose the Meager massif, with the Bridge River Vent being the most recent to form. It is the only vent of the massif to exhibit volcanic activity in the past 10,000 years and one of the several vents in the Garibaldi Volcanic Belt to erupt since the end of the last glacial period. The crater constitutes a bowl-shaped depression overlain by glacial ice and volcanic debris that were deposited during volcanic activity. Its breached northern rim has been a pathway for lava and ash flows that have traveled throughout the nearby Pemberton Valley.