This has been a summer of exploring Long Valley Caldera (looking for natural hot springs), and traveling to different craters. In the next post, I continue to visit craters in Oregon and Washington.
On the Summer Solstice, I continued my quest for a hot spring. I had found one the week before, see post about ‘Weekend Ramglings‘, but was directed to two others whose mineral content was mostly calcium. I found both, but they were so crowded with people, I didn’t even try to get in. In Long Valley Caldera, the forest service came through many years ago and cemented in real hot tub-like structures. They have hot water piped in from the slimy hot springs, some also have cold water piped in. I went back to the one I’d found while traveling Glass Mountain where obsidian abounds. There were several different people there, two couples, three students from Berkeley, a hermit, and two fishermen. It was a lovely solstice celebration and another great sunset.
Above the Caldera, Mammoth Mountain boasts many hot springs, and craters. I attended a geology hike there one morning. I’d been there before, but wanted to hear about the geologic changes that caused the craters first hand.
Panum Crater, created a mere 650 years ago, sits beside Mono Lake (created about the same time as Long Valley Caldera-760,000 years ago). This is an instance of many volcanos located close together (like Long Valley Caldera and Mammoth). A Rhyolitic Plug-Dome Volcano (I don’t pretend to be a geologist, so please open the above link for more information). What happens is that some of the heat of the volcano hits ground water, causing steam, some lava is expelled, cooling instantly, making light lava rock with air holes, but then the volcano is slowed down and the remaining lava cools more slowly, squeezing out the air bubbles and that causes obsidian. In Panum Crater, you can see the blown out sides, but in the middle are domes of rock and obsidian. It was difficult to capture it in a photo.
Sand tufa surround Mono Lake where the water level used to be. Salty lake water (carbonates) + freshwater springs (calcium) = Tufa (calcium carbonate).
Next time, Oregon!
from egghill 
Your description and photos makes me want to go there too. When I was growing up I spent many summers up at Clear Lake at my grandmother’s house. Across the lake is Mount Konocti which is an inactive volcano. http://volcanoes.usgs.gov/volcanoes/clear_lake/clear_lake_geo_hist_38.html Clear Lake is a crater as well. Clear Lake is the largest fresh water lake in California. There were a lot of “volcanic rock” there too, the black glass. And hot springs in surrounding areas. Also in Calistoga and environs like the Old Faithful geyser. So interesting. I think Mount Lassen is another volcanic area.
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Practically every area I drove through on my recent drive to Washington was volcanic! And two Crater Lakes (CA and OR) – who knew? Our geography classes as a kid didn’t get specific about that sort of stuff! I am constantly amazed.
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