Episodic eruptions during this phase of activity produced andesite and dacite lavas, as well as pyroclastic flows from Peléan activity. Later, the volcano was overridden by the Cordilleran Ice Sheet, which covered a large portion of western North America during glacial periods of the Quaternary.
During this phase of activity, eruptions produced andesite and dacite lava flows, as well as pyroclastic flows from Peléan activity. Later, the volcano was covered by the Cordilleran Ice Sheet, which blanketed a large portion of western North America during glacial periods of the Quaternary.