Volcano viewing is going on my bucket list

 kw: book reviews, nonfiction, earth science, geology, volcanology, planetology

My uncle was a professor of geology. He had a "volcano fund". Whenever he got news of an interesting volcano beginning to erupt, he would try to go to see it. This often required getting someone to fill in for him to teach a few days of classes. He had to be selective, with 20-40 or more active volcanoes spouting off on any given day. For example, "interesting" included "rather safe" and also, erupting day after day to give him time to get there and have a good chance of seeing the eruption in progress.

On the other hand, although I have degrees in geology, I have never seen a volcano erupt. Time's-a-wastin'! I'm not getting any younger, so I'd better get on the volcano grapevine. A big component of that grapevine is the Current Eruptions page at the Smithsonian Institution, something not available when my uncle was alive. The map shows the current situation as of April 15, 2024, of volcanoes that are "in continuous eruption", but you need to read the definition of continuous…

Dr. Robin George Andrews is certainly on that grapevine. He's in the enviable position of being able to go see volcanoes pretty much at the drop of a hat. His book Super Volcanoes: What They Reveal about Earth and the Worlds Beyond brings us very informational stories about what volcanoes are, where they are to be found, and how they help us discover the dynamics of a planet. By the way, note that the title is not Supervolcanoes but Super Volcanoes, as in "Volcanoes are Super" but with a less juvenile connotation. Supervolcanoes, including Yellowstone caldera, occupy one chapter.

An example of seeing the dynamics of Earth is quite visible in the map above: the "ring of fire" around the Pacific Ocean. This has been known about for centuries, but it was only explained after the discovery of plate tectonics in about 1960 by Marie Tharp and others. The Pacific Ocean is slowly shrinking, being "subducted" under moving plates bearing the continents all around it; the Atlantic is growing at the same rate. The motions are mostly in the range of 2-5 cm/year, about the speed a fingernail grows. The very different style of (now extinct) volcanism on Mars and Venus indicates that plate tectonics did not happen on those planets, or if it occurred very early on, it didn't last long, and hasn't operated for at least three billion years.

By contrast, this image of the moon Io shows us a smallish body with a surface that consists entirely of volcanoes and lava flows. The blue plume is an erupting volcano. Although Io doesn't seem to have plate tectonics, it is kept hot (about the boiling point of sulfur: 445°C or 832°F). How? Its orbit around Jupiter is elliptical, and the orbit is kept from being "rounded out" by resonance with the orbits of its sister moons. The elliptical orbit results in tides that stretch and squeeze Io, heating it halfway to boiling in the process. For the curious, Io is pronounced "EE-oh".

You may have heard that some of the moons of Jupiter and Saturn have subsurface oceans, probably of salty water beneath a thick (20-50 km) crust of ice. Io has a subsurface ocean of molten rock! Actually, it is kind of a slushie with crystals of high-temperature minerals in a broth of lower-temperature mineral melt.

Earth has three ultra-famous volcanoes. One of these is Kilauea, in Hawaii. It is huge, and it tends to erupt more than half the time. For the past several days it has not been erupting, but mini-earthquakes are going on all the time, indicating that magma is moving around beneath the crater. It could start again any time, and it might then erupt for a few days, or months, or even several years.

The most beautiful volcano, in the eyes of many including me, is Fujisan in Japan. It is often called Fujiyama, but in Japan most mountains are given the suffix "san" rather than "yama". Both suffixes mean "mountain". This view is from the southwest end of Ashinoko ("foot-shaped lake"), in the Hakone area, a national park. I have seen this view from this spot, but in the springtime, when these maple trees were green. Fujisan is considered dormant, but it is not entirely inactive. Its most recent eruption was in 1707.

The most feared volcano by many, the one usually called a supervolcano, is the Yellowstone caldera in northwestern Wyoming. This is one of several, probably at least 20, on Earth. The Supervolcano page of Wikipedia states that at least 60 "VE8" eruptions are known to geologists. The Volcano Explosivity Index is logarithmic, and the biggest events, dubbed VE8, yielded at least 1,000 cubic km of ejecta, either lava or ash or both. The most recent such eruption was 26,500 years ago in New Zealand. Of the five known VE8-size eruptions by the Yellowstone hotspot, which has moved across the northern US for 40 million years, the most recent was 640,000 years ago, and barely makes the grade as a VE8. The largest known eruption from this hotspot occurred just east of southern Idaho, and was about three times that size, 2,800 cubic km. That makes Yellowstone a rather small supervolcano! At least four supereruptions elsewhere exceeded 5,000 cubic km, and two, one in Canada (half a billion years ago) and one in Indonesia (75,000 years ago), may have exceeded 12,000 cubic km of ejecta. For reference: the abyssal plain of the Ocean has an average depth of about 4.5 km, so 12,000 cubic km would fill 2,650 sq km of the ocean, or about 40% of the area of Delaware or 65% of the area of Dubai.

The author discusses the Yellowstone hotspot and other hotspot supervolcanoes for a full chapter, and tells us we have little to fear from Yellowstone. The hotspot's current location is at the eastern edge of the Yellowstone Caldera, and it is moving eastward a few cm/yr. To be accurate, hotspots don't actually move, the continents above them move. The North American Plate is moving almost due westward, while the Yellowstone hotspot periodically pushes magma into the crust and starts a new volcanic province, at intervals of about a million years. The current motion is bringing a thicker piece of very resistant crust over the hotspot, and it may not be able to cook its way through the crust again until the rest of the continent crosses over it, in 60 million years or so.

There is much, much more, but this is a taste. Super Volcanoes is super fun to read. A final volcano image, this one imaginary: