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| Clear Lake Volcanics |
Hi All. The trip Petra and I took Saturday was for the purpose of looking at some volcanic rock formations along Highway 29 in the Clear Lake volcanics area. We must have passed them, which for the most part may have been a good thing. The areas we did see were right up against the road and no place to pull over in the immediate area. That meant we would had to have walked on the road, which I don’t think would have been a good idea. One of the features that stands out in the Clear Lake area is Mt. Konocti. You can’t miss it. It sticks out like a sore thumb. Depending on who you talk to the volcano is still active, but sleeping at present time to being inactive. In the 1980s harmonic tremors were recorded in the Clear Lake area. They lasted about 15 minutes. To the best of my knowledge that has been the only time they were recorded. I will have to check on that again. Mt. Konocti, one of the most visible examples of the Clear Lake Volcanics, is an inactive volcano that still preserves its volcanic form. The Clear Lake Volcanics are mostly silica-rich volcanic rocks (e.g. obsidian) located in and around Clear Lake, but they also include some basaltic rocks as well. These volcanic rocks are about 10,000 years to 2.25 million years old. For the past million years or so, the main center of volcanic activity has been south and east of Clear Lake. Interbedded with the Clear Lake Volcanics is a Pliocene-Pleistocene sequence of lake and streambeds, approximately 2 km thick, the Cache Creek beds. It is thought to have been deposited in a fault-bounded depression (Graben) east of present-day Clear Lake. It's not clear whether these sediments connected with the Tehama sediments to the east (e.g., in the Winters area). Pyroclastic deposits are rare in the Clear Lake Volcanics, unlike the Sonoma Volcanics. For those who are interested in roadside geology you might find the link to be interesting. It was what prompted the trip to start with. Take Care…Don in creepy town http://www.ncgeolsoc.org/Clear%20Lake%20Volcanics%20FT.htm |
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