Aerial view of ash-covered Crater Peak after an explosive eruption on September 16-17. Before the 1991-1992 activity, a small pond covered Crater Peak's crater floor; it disappeared shortly before the first eruption on June 27. After the September episode, scientists estimated that the crater was filled with explosive debris to a thickness of more than 20 m.

Crater Peak vent is the youngest volcanic feature at Mount Spurr. It's a flank vent that occupies the breach of a large caldera formed by a large landslide and explosive eruption of Spurr. Crater Peak began erupting at least 6,000 years ago; an earlier cone built in the same location as Crater Peak has ben mostly destroyed, presumably by glaciation.

Crater Peak has been the source of all eruptive activity at Mount Spurr in the past several thousand years.