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Bogoslof Volcano

June 19, 2017

You may (or may not) have noticed that I have been absent from the R&C blogs for quite some time. What can I say? I had cancer surgery in December of 2014, which caused it to snow and delay my escape departure from the hospital. Back surgery for a major broken disc took place barely a year later, which also caused it to snow. I tore a rotator cuff the day of back surgery. That was repaired about 8 weeks later, well into the springtime to prevent further snowing. Then a second rotator cuff surgery about three months later, when the original repair popped loose. Sometime about August of 2016, I realized that I had been taking pain killers for more of 2016 than I had been without them. Any blog I might have written would have been pretty random.

One symptom of rotator cuff tears is that it keeps you awake. Pain is bigger at night. That’s when I started reading Twitter. Late at night, 140 characters are just about right for reading material. If you’re full of pain killers and muscle relaxers. And if you can only use your left hand because your good hand is in a sling.

Much of my Twitter feed is geologist friends, and scientific societies like the American Geophysical Union and the Geological Society of America . The ones I follow most closely are from the United States Geological Survey- the volcano observatories and the seismic alert network. Yes, kids, that’s entertainment to me, perhaps more of an anti-social media than social media. Other people follow actors and actresses, or comedians, or political figures, but I’d rather know what’s shaking and blowing up.

My Twitter feed has been full of the eruption of Bogoslof volcano, a 6,000 foot tall edifice, of which only 200-300 ft. peeks out above sea level. It was named by Russians when it surfaced during an eruption in 1796. There’s lots of Russian names scattered through the Aleutian Islands because they were first explored by Vitus Bering, a Danish cartographer serving Tsar Peter I. The Bering Sea and Bering Straits were his greatest hits.

Geologists are interested because the Aleutians are an island arc, explosive volcanoes that form over a subduction zone. During tectonic collisions, island arcs are jammed onto the edges of continents. It’s one way the continents get bigger.

NC map2

Volcanic island arc rocks of the Carolina Terrane are shown in blue-green. Pink shows granite about 300 million years old, and dark brown shows Triassic Basins. Dark blue is the edge of North America, and gray is terranes that may or may not be North America.

North Carolina’s own Carolina Terrane is one example. It collided with North America about 450 million years ago. It’s of interest to geologists and everyone else as the real estate where most of North Carolina’s gold is found.

At iris.edu, you can use the 3D seismic viewer  to look at the downgoing oceanic slab north of the trench. To find Bogoslof, first find the Okmok Caldera (classic volcanic mountain with circlular hole on top) on northern Umnak Island. Bogoslof is north of that. On the next island east, Unalaska, you can follow the outlet of the Makushin Bay west to Bogoslof. It works best if you pick a high number of earthquakes, press “Apply”, then push the “3D view” button. With the mouse, you can “grab” the S (for South) and flip it up and rotate it.

Aleutian earthquakes

Looking below the surface at the earthquakes shown above. Light blue line is, again, the deep trench. Away from the trench, earthquakes accompany the oceanic crust as it dives back into the mantle. The islands in white are volcanoes above this subduction zone. Graphic created with the 3D Seismic Viewer, Iris.edu.

Earthquakes mark the top of the slab. As it descends, it releases water that causes melting, and the melt migrates to the surface as magma. The slab in this area is very steep, so the line of volcanic islands is fairly narrow.  Volcanoes are basically a pipeline to return water and carbon dioxide to the surface.

The excitement started on 16 December of 2016, although when they looked back, unrest started earlier in the month. Since then, there have been more than 40 explosive eruptions.  One big burp of sulfur dioxide gas was followed by satellite from Alaska to Nebraska.

Bogoslof volcano is fun because it’s so far away from anything that it’s only monitored remotely. It has to be monitored, because it can blow ash high enough that the cloud can disrupt airline traffic. Ash clogs the jet engines, then melts in place so that the engine is dead. Volcanic gasses tend to be very acidic, which isn’t exactly the cure for engine trouble. Finally, all the windshields get sandblasted. So the Alaska Volcano Observatory (AVO) pulls out all the stops. Seismic, satellite, infrared, infrasound, lightning detection, and a few pictures taken from Alaska Airlines flights or Coast Guard boats. Much of this is available online, so you can track as the island is blown up and rebuilt on a weekly or daily basis.

May eruption Bogoslof Island

Remote sensing of a Bogoslof eruption. Seismic shaking and infrasound (low frequency, below human hearing) of the May 8 eruption. Seismic data shows what happens below the ground, and infrasound what happens above. Lightning is the result of ash particles rubbing together. Graphic courtesy of Alaska Volcano Observatory, credit John Lyons.

It easy to remember that the Year Without Summer, 1816, was the result of the eruption of island arc volcano Mount Tambora. Volcanic aerosols lowered global temperatures enough to cause worldwide famine and crop failures. Farmers in North Carolina suffered poor crops, but farther north and at higher elevations, there were no crops. I suppose I watch volcanic eruptions for the same reason people watch weather forecasts.

Volcanic eruptions are good for the spirit, too. They remind me that the Earth is alive, living on a time scale much different from the regimented days and weeks of human time. The Earth’s clock creeps and jerks erratically, but there is always lots of time. Plenty of time. That’s a good thing to remember. There’s always something going on, especially when you’re stuck in bed, flat on your back.

 

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