Andes Supervolcanoes


Don’t panic, but we’re living in an age of supereruptions.

Seriously, don’t panic.

It’s taking place on Earth’s time scale, not our own — we’re not talking days, weeks, months, or even human lifetimes here.

According to Mason et al. (see source list), this “age” has lasted 13.5 million years –a time span only geologists could call short. And it includes fewer than 20 supereruptions.

Granted, it would only take one to ruin our interconnected world, but no supervolcano has uncorked during recorded human history.

Even better, volcanologists monitoring known fire giants like Yellowstone report no signs of imminent trouble.

It’s not easy for us to get a feel for geologic time.

And yet, while the idea of a supereruption is exciting (and scary), the long view is essential if we’re going to really understand these extreme but rare events.

Los Frailes, with a volume of some 2000 km3, per Kato et al., is one of the older ignimbrite complexes in the Central Andes. The youngest eruption here is over a million years old. (Image: William Seager via Wikimedia, CC BY-SA 3.0)

Many of the supereruptions have happened in the Central Andes, where a “flare-up” left an estimated 31,000 km3 of ignimbrite (Freymuth et al.) filling up valleys or piled high into plateaus like the Friars (Los Frailes) Plateau in Bolivia.

For comparison, the 1980 Mount St. Helens eruption produced about 1 km3 of tephra.

Yellowstone’s Huckleberry Ridge eruption around two million years ago had a volume of 2,200 km3.

Huckleberry Ridge was larger than any single South American supereruption (though some of those have come close to it).

However, the Andean subduction-zone supervolcanoes outnumber the Yellowstone hot spot and so it is that a sizeable chunk of central Andean real estate sits underneath some 160 feet of ignimbrite on average. (Salisbury et al.)

Incidentally, volcanic activity at the Los Frailes complex concentrated huge amounts of silver and other metals that conquistadors eventually found and used to fund their New World empire.

They experienced no supereruptions.

Indeed, supersized pyroclastic density currents have not ravaged this beautiful landscape for at least a million years — supervolcanism peaked in the Central Andes roughly 8, 6, and 4 million years ago. Then things quieted down, although “normal” volcanoes regularly erupt there.

But as we’ll see later in this series, in some parts of the Central Andes those great subterranean fires are not yet extinct.

The Central Volcanic Zone

The Pacific seafloor has been subducting beneath the western edge of the South American continental plate since at least Jurassic times.



Now you know how South America and Africa used to fit together!


Until recently (in geological terms), that seems to have been a fairly quiet process. But changes in tectonic plate configuration and speed, as far as I can understand it, led to the rise of the Andes.

The northern and southern zones are fairly quiet, but again, for plate tectonic reasons, the central Andes volcanic zone has been quite lively.

Unfortunately, there are no general-interest videos about this on YouTube, but the first 3-1/2 pages of this presentation about the Andes supereruptions is interesting and helpful. (Things get technical towards the end of the fourth page.)

I’m going to leave you with that link, because there are a LOT of ignimbrite eruptions and ancient supervolcanoes in the Andes. There’s a lot of cutting-edge research going on, too.

Over the rest of the month, we’ll just touch on some of the biggest supervolcanoes and then close this “South American Supereruption September” with a look at what might possibly be the next site of activity.

Coming up next is La Pacana Complex, the largest and, I think, the most productive source of supereruptions in the Central Andes.

To prepare ourselves for the scale of these things, let’s look at a caldera in Utah volcanologists recently found.

This was from a different and older ignimbrite flareup that happened in North America long before the Andes appeared.



This was a huge eruption. For contrast, the Toba supereruption 74,000 years ago had a volume of “only” some 2,700 km3.


Featured image: Fearghal O’Nuallain, CC BY 2.0.


Sources:

Freymuth, H.; Brandmeier, M.; and Wörner, G. 2015. The origin and crust/mantle mass balance of Central Andean ignimbrite magmatism constrained by oxygen and strontium isotopes and erupted volumes. Contributions to Mineralogy and Petrology, 169(6): 58.

Kato, J. J.; Kay, S. M.; Coira, B. L.; Jicha, B. R.; and others. 2014.
Evolution and geochemistry of the Neogene Los Frailes ignimbrite complex on the Bolivian Altiplano plateau. XIX Congreso Geologico Argentino.

Mason, B. G.; Pyle, D. M.; and Oppenheimer, C. 2004. The size and frequency of the largest explosive eruptions on Earth. Bulletin of Volcanology, 66(8): 735-748.

de Silva, S. L. 1989. Altiplano-Puna volcanic complex of the central Andes. Geology, 17(12): 1102-1106.

de Silva, S. L., and Gosnold, W. D. 2007. Episodic construction of batholiths: Insights from the spatiotemporal development of an ignimbrite flare-up. Journal of Volcanology and Geothermal Research, 167(1-4): 320-335.

Salisbury, M. J.; Jicha, B. R.; de Silva, S. L.; Singer, B. S.; and others. 2011. 40Ar/39Ar chronostratigraphy of Altiplano-Puna volcanic complex ignimbrites reveals the development of a major magmatic province. Bulletin, 123(5-6): 821-840.

Volcano World (Oregon State University). 2008. Frailes Plateau Last accessed September 4, 2019.



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