Clear Lake Volcanic Field

Volcanic history of Mount Konocti

Mount Konocti is a 1,312 m (4,305 ft) mountain that dominates the view of the eastern shore of Clear Lake. It began forming its major edifice approximately 350,000 years ago, though core samples have been dated to 480,000 years ago. 

Mount Konocti on the western shore of Clear Lake, California

Mount Konocti, a mostly dacitic composite cone, on the western shore of Clear Lake, California. The round flat-topped hill in the foreground with a small right peak is a maar volcano.

(Credit: Donnelly-Nolan, Julie M. Public domain.)

Dacites from these early forming eruptions vented in a west- northwest-trending zone, which culminated at the northwest end of the Mount Konocti edifice. This mountain contains the largest volume of dacite in the Clear Lake Volcanic Field and must have been fed from a sizeable magma chamber. However, the interspersed mafic units show that Mount Konocti was beyond the northern limit of the chamber at that time and was thus fed laterally from the main chamber. Even today, Mount Konocti is beyond the inferred northern limit of the present magma chamber.