Mount Konocti which is on the Pacific Ring of Fire, may have spewed out molten lava as recently as 200,000 years ago. Mount Konocti sits several thousand feet above the surface of Clear Lake on the eastern flank descending directly into the murky, green-brown water. Even though Mount Konocti is not currently active, its volcanic heat still shows evidence of the activity below the lake. Only about 8 miles under the lake is an active magma chamber, and the waters of Clear Lake bubbles from fishers below that are releasing gas from the magma chambers below.
Even though there is evidence of activity around Clear Lake especially around Soda Bay, there is near the middle of Clear Lake a thermal spring from a fissure that is on the lake bed that creates a bubbling cauldron on the surface, which indicates the continuing volcanic activity. There are many bubbling fissures that help add effervescence to Clear Lake, but this particular vent is one of the biggest of all. About 35 feet below the surface is a thermal spring which jets from a great hole in the bottom of the lake.
In the 1990’s scientist decided to dive and made several tricky descents into the opening of the fissure and described a pulsing cycle in which a few minutes of vigorous bubbles and alternated with modest bubbling. The divers were pushed upward with a strong water current toward the surface, while along the wall of the opening pulled downward into the lakebed fault. It was about 65 feet into the fissure , the narrow tube broadened into a 20 foot fissure where the water was emerging forcefully through a bottom of soft clay. In the chamber there was no gas bubbles, except on one ocassion when a diver reported that he got hit in his face mask with a bubble that was reported bigger the the divers head.
For now the gas emitted from this fissure had not been analyzed, but many other springs in and around the lake releases bubbling water that is rich in various healthy minerals that provided Clear Lake with its former days of glory.
Clear Lake’s basin was formed about 2 to 3 million years ago. It is extremely rare for a lake to exist that long. Clear Lake has remained because its lakebed is self adjusting and sits in a fault controlled basin. The faults along its northern edge comprise as a “trap door graben” that sags downward under the immense weight of the sediment. So the lake floor drops at the same rate that the sediment washes in. As the old faults maintain Clear Lake’s ability to hold water, the younger faults protect it from geological complacency. The active Konocti Bay fault, which is related to the San Andreas Fault, runs north westerly into the middle of the lake which produces the fissures that helps make Clear Lake a bubbling cauldron.