Hoodoo Mountain is a well-exposed example of peralkaline, phonolitic ice-contact and subglacial volcanism. Studies have shown that a cycle occurs about every 24,000 years, after which activity shifts from subglacial to post-glacial eruptions and then back to subglacial again. This cyclical activity is unique to Hoodoo Mountain among the Northern Cordilleran volcanoes. Three cycles have been clearly identified, including one subglacial eruption and two post-glacial eruptions. Records show that from 85,000 to 80,000 years ago, activity was more intense than it is today. More than 90% of Hoodoo Mountain, which dates back to at least 100,000 years, formed during its early eruptive history and has grown steadily since then. Regional ice thickness during some of Hoodoo Mountain's subglacial eruptions might have been more than in thickness.