D-4: Waterbending

The following is Admiral  Howe’s second (and last) guest post on the series. Originally posted on the Stellaris forums.

 

Hello again! Admiral Howe here for a repeat performance. Thanks once more to The Beautiful Void for being gracious enough to offer me a turn in the rotation for his awesome series. He, single handedly, has made this period of super-hype go far more easily. Especially for my hype-addled mind. :D

So, last time I left you with doom, gloom, and a whole ‘die in fire’ motif. It wasn’t my intention to be such a gloom-bearer so, today, I’ll balance my firebending with a bit of waterbending.

Water? Really?

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Yes. Free surface water makes Earth the crown jewel of Sol’s system – a fact we all raise a drink to I believe. This gleaming azure orb spins through space draped in a mantle of 1,400,509,000 cubic kilometers of liquid water. That’s enough water to mantle Mars in oceans averaging 10km deep. (Take that Kim Stanley Robinson!)

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But that water is here and it’s vital to the biology we all rely on (and really, it would suck to try to move it). This information is nothing shocking to moderately well informed folks. Yet, like with volcanoes, that’s only a small portion of the story…for water plays a vital role in Earth’s geology. And that role is likely repeated on any water-bearing terrestrial planet.

You see, water runs this show.

Take these two winning folks here:

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and

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First you have anhydrite, also known as calcium sulfate, or CaSO4. Second you have gypsum, also known as calcium sulfate dehydrate. Yes, CaSO4*2H2O. Same chemistry as anhydrite but with a tiny amount of water added. In fact, anhydrite will spontaneously change to gypsum when exposed to water in normal circumstances – something we exploit in plaster of Paris.

But, more importantly here, the two crystals are different size – gypsum is considerably larger because of the absorbed water. The difference is enough that adding water to even the hardest rock rich in anhydrite will cause the rock to disintegrate in minutes as the gypsum crystals push apart the rock’s matrix.

Now imagine siting an important piece of infrastructure on bedrock containing anhydrite. Thank goodness no one would ever make such a mistake.

Mineralogical cycles and processes change dramatically when water is added in a vast number of contexts. Venus may be our twin in mass and density but the rocks and processes we find on her surface will never look like Earth. And Mars may have once been much warmer and wetter but in its desiccation even the rocks themselves changed as their water bled away.

Where this is most dramatic, and most impactful for us, is with the igneous rock known as basalt. I touched on these before when I mentioned the Siberian Traps as those Large Igneous Provinces are uniformly basalt and thus can flow for great distances until they cool.

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Once they do that water begins facilitating rapid weathering as the iron and magnesium rich basalt will react with most chemistries mobilized by water – especially if the planet also has oxygen available. In fact, the longer basalt is exposed to water – and water gets a chance to percolate through the cracks and fissures in the cooling rock – the more it can weather and alter the basalt into new minerals. And this is vitally important because the seafloor is uniformly basalt.

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This map shows the seafloor with the ages marked (key is on the bottom left). You can clearly see the globe-spanning Mid Ocean Ridge, the single greatest mountain range in the solar system, and you’ll notice the seafloor is brand new right at the ridge.

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We know these ages of the seafloor because of yet another mineral, an iron mineral named magnetite. This mineral earned its modern name because it is naturally magnetic (historically it is known as lodestone) and when it crystallizes it does so in alignment with the Earth’s magnetic field.

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Every reversal is recorded, world-wide, precisely on the seafloor because of this and – when combined with land-based research – lets us pin down the ages of most of the floor. It’s actually amazing that once we discovered this (another surprise from WW2) we not only rapidly established plate tectonics as our working theory of Earth’s crust, developed a magnetic-field calendar for earth to let us age-date large portions of the world, and also could establish spreading rates for the seafloor current and past (and find they’re not uniform).

While this seems like a neat aside, bear with me a bit longer…because water is responsible for this too. If you look back up three images and take a look at the ages of the seafloor something should jump out at you.

Go ahead, take a moment.

I’ll still be here.

Really, where would I go before Monday?

Yeah, you should have noticed it…on our 4.6 Gy planet the ocean floor is no older than about 200 million years. You’d think losing 4.4 Gy of ocean floor is embarrassing but, it’s not. It was a revelation.

What happens is after hundreds of millions of years of cooling and mineralogical alteration by water basalt reaches a point where it is now denser than the mantle beneath it. When this threshold is reached, even if there isn’t any plate collision pushing against the basalt, the seafloor falls away and begins sinking back into the Earth.

This is known as subduction and the pull of subduction is what powers the whole tectonic engine, from driving the continents across the globe to pulling open the Mid-Ocean Ridges and leading to new crust formation.

Just that by itself would be enough to keep me fascinated for a whole career…cold, wet seafloor diving into the abyss while causing new seafloor to be born thousands of kilometers away. A whole planet’s face constantly rearranging simply in response to this endless conveyor belt.

But wait, there’s more.

One more bit about water here and that’s what happens when the old seafloor begins its death dive. Increasing pressure and heat begins to force the water in the seafloor plate out and into the mantle. And there, like the anhydrite->gypsum reaction above, dramatic changes in the minerals take place.

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The first effect, and perhaps the more obvious one, is the water entering the mantle lowers the melting point of the surrounding rock. That melted rock is, naturally, more buoyant than the solid rock around it and it rises only to erupt in long chains of volcanic mountains mirroring the subduction off shore. It’s why the Ring of Fire is where it is and why, someday, a new one will form around the Atlantic when it’s that ocean’s turn to disappear again.

The second effect is the more profound one. As the melted magma rises it carries with it the water from the subducting plate’s water. This water changes the nature of the melt and thus the rocks being formed by the magma as it reaches the surface. Instead of basalt erupting the new melt – a combination of water, mantle, and melted crustal rocks passed through on the way to the surface – you get andesite and rhyolite. Or, more commonly, continental rocks.

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Oceanic crust never gets more than 5-10km thick, as shown above, but continents can grow over 70km thick – with parts of Eurasia potentially 120km thick. The reason for this is buoyancy once again. Continental crust is significantly less dense than the mantle and cannot be subducted baring incredibly specialized circumstances. Once you form continental rocks they remain for the rest of the planet’s life gradually accreting into larger and larger continents. And there lies what I think is the the biggest magic water has on the Earth…without the plate tectonic system we wouldn’t have the very continents as we understand them. Their diverse terrains, soils, climates, and resources are a byproduct of the tectonic system pushing and pulling them all over the globe.

All because a little water got into the system.

And somewhere out there, maybe Kepler 186f, this same process is building and reshaping the continental faces of unfamiliar worlds our descendants may one day lovingly call home.

Thanks for reading.

I would like to thank The Beautiful Void one more time for giving this rambling author a chance to guest spot his wonderful series.

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.

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“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.