Wednesday, January 22, 2014

Quake Activity Detected At Inskip Hill

About 20-25 miles WSW of Lassen Volcanic Center in Northern California lies a little known volcanic hill called Inskip. This is a Pleistocene volcanic cone complex which has had exactly no volcanic activity in historical time. Recently I have begun seeing some small quakes occur directly beneath it at a depth of about 3km, one of which occurred today at a magnitude of 2.2. This is probably nothing but it is always important to be vigilant when it comes to long dormant or presumably extinct volcanoes.


Location and magnitude of 2.2 quake under Inskip Hill, a presumably extinct volcano in Northern California near Lassen Volcanic National Park. 

While it is not at all probable that that these quakes of late are volcanic in nature, it is still possible. Inskip hill is not a well studied volcano. Indeed it was quite difficult to find any scientific or geologic information on the web, the only bit of info I found was at this link, where the volcano is described thusly:


"The hill is of volcanic origin and has numerous lava outcrops. It is part of a Plio-Pleistocene volcanic activity that began some miles to the east with the now vanished Mt. Maidu. From this cone issued first flows of basaltic andesite, followed by pyroxene andesite and dacite. Some 1.5 million years ago two enormous eruptions spewed forth rhyolite which covered some 180 square kilometers (70 square miles) to an average thickness of 152 meters (500 feet), followed by dacite avalanches which covered perhaps as third as great an area. The summit of Mt. Maidu collapsed, forming a caldera. Later came a series of basalt eruptions that built cinder cones with associated lava flows. Inskip Hill is one of these and dates to the mid or late Pleistocene. There are ice caves on the hill."

It is a bit puzzling as to why a well-preserved volcano such as this hasn't been more thoroughly studied, although the volcano does reside on private land, so I am assuming this is part of the reason.

For the past several weeks, I have seen some earthquakes pop off in this location, nearly directly under the summit of this volcano, or under its NE flank. While I am certain nobody is raising alarm bells over this (a magmatic intrusion would generate far more quakes, tremor, and probably GPS would detect ground swelling as CA is well monitored), it is still pretty interesting to speculate as to what could be going on down there. As some volcanoes have recently demonstrated (such as the abrupt and unexpected eruptions of Chaiten in Chile, and Nabro volcano in Eritrea), warnings are not always given when a volcanic system decides to reactivate.

Again, it is extremely doubtful that this is what is happening at Inskip, but perhaps blogging about these goings on might elicit some investigations, or perhaps some attention, by USGS (who as I recently found out, rather enjoy reading this blog!). In any case, I just thought this was an interesting opportunity to write about this very little known volcanic complex. I'm keeping my eyes peeled!

1 comment:

  1. Thanks for posting this info. I have always wondered why there was so little mention of this prominent landscape feature.

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