Volcanoes, more common than you might guess

 kw: book reviews, nonfiction, science, volcanology, volcanoes

My uncle, a geologist and geology professor, had a "volcano fund". He was ready, on short notice, to go wherever a volcano was erupting, to see it and study it. I have since learned that his fund was really just for "interesting volcanoes", or else he'd have seldom been at home. At any one time, at least twenty volcanoes are actively erupting, more than thirty have erupted within the prior week or month, and more than forty are considered to be "in continuous eruption status", according to the Current Eruptions site of the Smithsonian.

This map from the website shows the volcanoes in that status as of December 9, 2021

The symbol in the middle of the Pacific Ocean is for Kilauea in Hawaii, which erupted continually for 36 years, ending in 2018, and then started up again after a two year lull. The symbol near Africa is for the volcano Cumbre Vieja on La Palma in the Canary Islands, which erupted for 85 days, ending Dec. 13, 2021. It is considered in current eruption status because seismic rumblings haven't yet settled down, and it could erupt again in the near (very near) future.

At the peak of its eruption, the Cumbre Vieja volcano was amazingly active, as seen here. I think my uncle would have gone there, and perhaps stayed for most of the 85 days.

Whenever the map above is next updated, there is likely to be a new symbol for the eruption off Tonga that began just a day or two ago. It will be between the symbol at Hawaii and the next one to the southwest.

I learned much of the above from reading Super Volcanoes: What They Reveal about Earth and the Worlds Beyond by Robin George Andrews. This book surveys several kinds of volcanoes on Earth, including the largest of them all, totally hidden from view, that is the 40,000-mile-long system of mid-Ocean ridges. These are the "spreading centers" of plate tectonics, where bloops of magma are burped from the central crevasses of the ridge system to form "pillow lavas", and magma that cools against the sides of the world-circling slit below the crevasses forms sheet lava, which is brand-new oceanic crust.

At the opposite ends of the major plates, oceanic crust either dips below continental crust, such as off Japan and South America, or pushes one chunk of continental crust against another, raising mountains in between, such as north-moving India forcing up the Himalayas and the nearby mountain belts, which are still rising. The "ring of fire" around the Pacific Ocean is the volcanic expression of magma formed from the upper part of down-thrust oceanic crust and its burden of sediments, deposited during the tens of millions of years that the crust was crossing the ocean from the spreading center to the subduction trench.

The author doesn't dwell on the different kinds of volcanoes and their eruption styles to any great extent. That is a good subject for a different book. Rather, he aims to show how volcanoes are ubiquitous not only on Earth, but all over the Solar System. In many cases, such as the Moon and Mars, the heat engine inside the body has shut off, and the lava fields are old, very old. While there is a little evidence that tiny volcanic eruptions might be continuing on the Moon, the dark lava fields that form the "seas" (and the face of the Man in the Moon) are more than a billion years old.

He does spend a chapter on a curious volcano, Ol Doinyo Lengai, which is currently the only active carbonatite volcano on Earth. Carbonatite lava, a combination of lime and the silicates that form more ordinary lava, is less hot (only about 550°C or 1,000°F) than the "fast" lava at Kilauea, which is more than 1,100°C or 2,100°F. You still can't swim in it!

Out among the moons of Jupiter and Saturn, however, one finds cryovolcanoes that erupt warm (and sometimes downright freezing-cold) salt water. You might be able to swim there, as long as you can survive the surrounding vacuum! The "lava" erupting on Jupiter's moon Io is hotter stuff, or rather, several kinds of hotter stuff. Some is mostly molten sulfur, propelled by sulfur dioxide gas, with a temperature of a few hundred degrees. More "earthly" silicate lavas are also found there, with temperatures ranging up to 1,300°C (2,400°F), equal to the hottest eruptions on Earth.

What keeps Io hot? It is equal in size to the Moon, which has long been cold and dead (or very nearly so). Io zips around immense Jupiter every 42½ hours, and is in a resonant orbit with the next two moons, Europa and Ganymede, which have orbital periods of 85 and 172 hours. While all three (and the fourth major moon, Callisto) have orbits that are very nearly circular, as they swing by one another, tidal forces flex the moons. Io's crust rises ten meters or more each time, a few times weekly, causing internal friction that keeps it boiling hot and makes it the driest known body in the solar system. The smaller tides on the other moons seem to have kept them warm enough to have liquid oceans up to 50 miles deep beneath icy crusts. Europa in particular has a crazy-quilt surface that shows it is still active.

One very interesting (and reassuring) chapter describes the supervolcano known as Yellowstone. Or, according to the author, "former supervolcano". Yellowstone and Kilauea share this characteristic: both sit atop mantle plumes, which are apparently stable features of Earth's mantle, dredging up material from an area nearly as deep as the core-mantle boundary, and depositing it atop the crust. There are about twelve plumes known, and the one under Hawaii is the most active at present. As the Pacific plate moves along, the plume pops through from time to time ("time" meaning a million years or so), to produce a new Hawaiian island. The chain of islands and former islands (seamounts) stretches all the way to the Aleutian Trench off Alaska. 

As the North American plate moves along, the Yellowstone plume does something similar. There is a chain of old calderas stretching at least as far as Idaho, and possibly much farther. The author thinks the current round of Yellowstone volcanism ended more than half a million years ago, and if the plume busts through again, a couple of hundred miles to the east, it will have some pretty tough, old continental crust to punch through. It may instead just "plate" material against the bottom of that section of crust for a dozen million years, which will gradually raise the elevation of the northern plains. Just wait about 350,000 generations and we'll see what happens!

These are just tidbits from the flood of information in this book. When I saw the book's title, I thought it would have a lot more sensational stuff to say about Yellowstone. I didn't consider that the main title is two words. But they are apropos: Volcanoes are indeed super! They keep the planet interesting, and their role in releasing heat from below, and also gases such as water and carbon dioxide, moderate the atmosphere and oceans in favor of most living things, at a tragic cost to a smaller number of living things that happen to be "too close" when an eruption begins.