D-11: It Came from the Core

The following is another guest post, by a gentleman known as Admiral Howe on the Stellaris forums, who will talk to us about geology. It was originally published on the Stellaris forums as part of this series. Republished here with permission. Thanks once again, Admiral Howe.

 

Greetings all. Today I’ll be your guest host at the incredibly gracious request of TheBeautifulVoid. What I’m going to discuss today is a bit of planetary mechanics, or why spreading your species to the stars is a good idea.

Specifically, we’re talking about volcanos and the existential threat they can pose to the inhabitants of a planet.

First I’d like you to think about what, exactly, is a volcano? Your impressions will vary a bit based on each of your experiences but, ultimately, all of you should have about the same idea. And, that idea is overly complicated because what a volcano really is simply is a method the planet is using to dissipate heat. (A recurring theme in the geosciences actually). And they’re incredibly effective at their job – maybe even too effective if you live near one. That such a simple goal could manifest into a mechanism that has been inspiring fear and awe for the whole of history can be attributed to volcanoes having the best special effects budgets in nature.

[IMG]
“The Tungurahua volcano spills incandescent rocks, ash and black smoke in a photo taken from Huambalo, Ecuador, March 6, 2016.”

All jesting aside, volcanoes are a fact of life on any body that has internal heat. Earth (my presonal favorite), Venus, Io, Enceladus are all volcanically alive today while the Moon, Mars, and (potentially) a few of the outer moons were alive in the not too distant (geologically speaking) past. And this poses a problem for any civilization as ours has had a number of major events/setbacks linked to these major eruptions. The classical Dark Age around the collapse of the Minoans and covering the whole eastern Med – likely the eruption of Thera in the Aegean. Fall of Constantinople – final year of the siege coincided with a volcanic winter brought on by Kuwae. I could write several articles on that alone, but that’s not the focus here.

Before you think we’re less vulnerable than our ancestors, I ask you to think again. In many ways we’re more vulnerable as volcanic ash shorts out electrical lines better than just about anything we’ve found and chokes engines with amazing efficiency. And in our world of “just in time” supplies, a region losing shipments can quickly spawn health and hunger issues of immense proportions. Could humanity survive? Sure, but only depending on the scale of the event.

What’s the scale we’re talking about here then?

So how do we talk about the scales of eruptions? Best way I’ve found it to use real world examples, so to start that’s where I’ll go. If you mention a volcano to someone in North America and it’s likely they’ll think of Mount Saint Helens in 1980. In that eruption the northern face of the mountain disintegrated and blasted sideways while the core of the mountain erupted vertically in an ash column 24km in height. Ultimately, the energy released was equivalent to 1600 Hiroshima bombs…and was released in a bit under 15 minutes.

It also didn’t hurt that it was the first big eruption of the television era in a nation awash with cameras.

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Mount St. Helens before and after the 1980 eruption.

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Ash fall from Mount St. Helens.

I know all that may sound impressive but if you didn’t live in the Pacific Northwest you likely didn’t notice more than a slight dip in temperatures for several months and some glorious sunsets until the ash cleared out of the upper atmosphere. After all, we’re only talking about 1.1 cubic km of rock-turned-to-ash here (and another 5 cubic km or so of trapped gasses released).

So, then…what’s the big deal?

The big deal, or why I started here perhaps, is that St. Helens – for all the destruction it caused – came in only as a 5 on the scale we use to rate volcanic eruptions. About the same as Vesuvius actually, but far better studied because of its recentness. See, volcanoes of that power happen about every 12 years around the world so while they’re big news in the region where they happen they’re common enough overall to be background noise on a planetary scale.

And yes what I’m calling background noise is still a staggering 8 cubic km of rock and ash, 40 cubic km of gases, and roughly 13,000 Hiroshima bombs worth of heat injected into the atmosphere every century. Thankfully, a planet is a big place and absorbs it quite easily. No, the reason I started here and mentioned this is because Mount St. Helens is a 5 on the scale…a scale that goes to 8. And is logarithmic.

Volcanic Explosivity Index

Wait then, what’s a 6?

Well the most recent one was Pinatubo in the Philippines. It erupted some 10 cubic km of material and injected enough particulates into the upper atmosphere to lower global temperatures 0.5C for nearly three years. I could go into depth about it but I’d rather talk about another recent 6…Krakatoa (Krakatau).

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Krakatoa/Krakatau showing outline of pre-1883 island.

Krakatoa, an island in the Sunda Straight, was known to be unstable for centuries. Dutch travelers remarked in 1680 that the lush, green island had been burned crisp…the vegetation quite dead. Dutch traders reported local history recording at least 9 eruptions between 400 and 1600. And a good translation of Krakatoa comes across as “The Fire Mountain”. So, yeah, people knew not to trust this island.

Which is all well and good, give it space and it won’t bother you. Right? Well, that largely worked until the night of August 26th, 1883. In the span of four vast eruptions the island vanished with a force in excess of 13,000 Hiroshima bombs (so yes, the average century output of level 5 volcanoes in one event). Ships were found miles inland, washed inland on massive tsunamis, some 600 villages and towns vanished. This eruption still holds the record for most-distantly heard sound…people in Perth Australia 3100km away heard it as did those near Mauritius 4800km to the west.

Tidal gauges in places like the English Channel recorded the shock wave pass…seven times as it echoed around the world over the next five days. And world weather took five years to recover from the – though the brunt of the 0.3C drop in world temps only lasted about a year.

And the craziest part, at least to me, is reappearance of the volcano’s core in 1927. It’s already back to 300m in elevation and slowly recharging, waiting for its next turn. And since tier 6 volcanoes happen once or twice a century, who knows, Krakatoa’s turn may be sooner rather than later.

But that’s only a six, the list goes to eight.

So, ladies and gentlemen, I’d like to introduce our exemplar for a type 7 volcano…Tambora, Indonesia.

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Tambora, Sulawesi Indonesia

Oh, don’t mind the picture…the upper third of the mountain has been missing since 1815 when it erupted over 100 cubic km of ash and rock over the span of a few days. The eruption column has been estimated to have reached 43 km into the atmosphere, think about that compared to modern jet cruising altitudes for a moment. This eruption led to the “Year without Summer” in northeastern United States where the summer of 1816 saw temperatures struggle to get above freezing. And there was even a great “fog” covering the sky for most of 1815 and 1816 that dimmed and reddened the sun – so much so people could view sunspots directly.

All that from one seven.

Fortunately for us, sevens happen only once or twice per millennia. Which is really for the best, I don’t think we’re all that well positioned to deal with them even as infrequently as they happen.

And for those curious, the energy released here was roughly 10^20 joules, or the equivalent of about 2.2 million Hiroshima bombs.

So, thinking of moving off world yet? Terrestrial planets are nice but they have their downsides…and we’re only to seven on our eight point scale.

So then, what’s an eight?

Doomsday, as one of my professors put it.

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Looking across the Yellowstone caldera. Yes, everything in this picture is part of the volcano.

The category 8 volcanoes, like Yellowstone pictured above, are massive complexes where the eruptions release rock and ash in the thousands of cubic km (on the small eruption end) from their calderas. Yellowstone is particularly interesting to me both in its proximity and in how reasonably well it’s mapped and understood. Unlike the smaller ones listed above Yellowstone is actually tied to a hot spot – essentially a river of slightly-hotter magma extending upwards (we think) from the core/mantle boundary.

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Cut-away showing an artists interpretation of the magma-chamber complex below Yellowstone.

And this river essentially blow torches its way through the overlying crust – sometimes gently in the case of Hawaii and other times with violence like here. If you know what to look for you can actually trace the motion of the overlying plates across these seemingly-fixed plumes which, while good for research, doesn’t change the problem presented here. Yes, the hot spot creates the volcano but it also is constantly refreshing its magma…Yellowstone has a recharge and release timer of about 700,000 years.

So how bad can it be, really? Well Tambora was around 100 cubic km. Two of Yellowstone’s last three have been 1000 cubic km and 2500 cubic km. One of those today would largely destroy the ability of North America to host modern life for decades…and there’s nothing to be done to prevent it. At least with modern technology.

And as for an energy-released estimated, let’s be honest, they’re really irrelevant at this point.

Space doesn’t sound as scary, does it?

It should, really. Especially with nice, shiny FTL ships. Oh and perhaps because I’ve left one little problem off this discussion until now. I mentioned that the index we use goes up to 8. Well, volcanos are illiterate and haven’t actually read the list…there are things worse than 8.

Folks, to wrap this up I present the Siberian Traps.

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Estimated extent of Siberian Traps based on surviving rocks.

The Siberian Traps, and eruptions like her, are often called large igneous provinces or flood basalts. Traps, here, is taken from Swedish trappabecause of the step-like formations left behind often leave distinctive step-like layering making them easy to spot with some training.

Now, the output of eruptions like these are measured in the millions of cubic km and they can have durations pushing a million years. Imagine, having two or three Mount Saint Helens going off per year, every year, for a million years. I’d board a colony ship at that point.

These massive events don’t have a well understood mechanic set yet and it’s doubtful we would be able to image a nascent one in the mantle. At least with any degree of certainty. Not that it matters, if one began there’d be nothing we could do to stop it.

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And all this goes on just so the planet can get rid of a little heat.

Thanks for reading, it was fun to dig through notes and texts too rarely read nowadays. And than you again TheBeautifulVoid for letting me guest a spot and help explain why heading into space isn’t such a bad idea.

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