Sorry, but earthquake swarms & harmonic tremor are two different things!
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- An hour east of Barstow, the Amboy cone is impressive from a distance.
http://www.sandiegoreader.com/news/2012/jul/19/travel-california-active-volcanoes/There are more than 550 active volcanoes in the world, five of which are in California. It's to be expected from a state sitting on the eastern edge of the Ring of Fire.
Between Barstow and Needles, California, just south of Americana icon Route 66 and east of the Mojave National Preserve, lies the Lavic Lake volcanic field. Here the Pisgah and Amboy volcanic cones sit amidst almost 30 square miles of basalt lava flow, housing lava tubes and caves.
One of two volcanic lava fields along the historic Mother Road (now part of the National Trails Highway System), most of the Lavic Lake field sits on private land. That doesn't seem to deter people from exploring the tubes and caves, or hauling away collectable stones from the historic Lavic Siding, the largest jasper deposit on the planet.
The 250-foot Amboy cone, however, is owned by the Bureau of Land Management (BLM) and is publicly accessible. The three-mile round trip trail takes visitors into the heart of the cone, onto the ancient lava lake and down in the center of it. The last eruption is estimated to have occurred 10,000 years ago.
The International Monitoring System (IMS)'s global infrasound network has 60 international monitoring stations working in unison to detect erupting volcanoes. The Amboy Volcano, with its tumuli and pressure ridges (visible on the eastern side of the highway), isn't on their radar screen. Nor are the 40 cones to be found in the Cinder Cones National Natural Landmark, south of Route 15 and the town of Baker within the Mojave National Preserve. There are plenty that are, however:
Obsidian-studded Coso Volcanic Field in Inyo County, for instance, is one of the most seismically active areas in the U.S. Here, earthquake "swarms" (technically, harmonic tremors – long-lasting seismic releases with distinct spectral lines that precede or accompany volcanic eruptions) are a weekly occurrence. Yet CalVO only ranks this site as a moderate threat.
Seismic and geothermal activity is rampant throughout the Sierra Nevadas, as indicative of the Mono–Inyo Craters, a volcanic chain of craters, domes and lava flows that stretch 25 miles from the northwest shore of Mono Lake on the eastern side of Yosemite National Park to the south of Mammoth Mountain.
The Mono Lake Volcanic Field within the Mono Lake Tufa State Nature Reserve consists of two phreatic (steam) volcanic islands in the lake and a cinder or "red" cone on its shore.
The Long Valley Caldera (aptly translated, "cauldron") east of Mammoth Mountain that encompasses these areas is one of the longest depression left behind by volcanic eruption in the world and is ranked a high to very high threat potential by CalVO – it's considered a super volcano capable of an eruption 1,000 times more powerful than that of Mount St. Helens.
Ironically, it is one of the most serenely beautiful, awe-inspiring areas of the state I've visited to date.
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