Is there glass in game of thrones

Game of Thrones is back for its penultimate season, and as ever, it promises to break the hearts of viewers up and down the land – and maybe, just maybe, give them a little bit of rare hope too.

I’ll admit it: I’m a casual viewer of the series, not a dedicated fan. I watch it when I can, while lamenting the fact that I’m too far behind the curve to properly catch up. The Internet – something which I’m never quite able to pull myself away from – spoils stuff far too quickly anyway.

Nevertheless, I recognize that it’s a seminal TV series, with a rich backstory and a diverse mythological world, fleshed out by the original novels. It’s got dragons, White Walkers, Children of the Forest, and dragonglass. In fact, that got me thinking – dragonglass has another name, “obsidian.” That piqued my interest, and made me wonder: what's up with the volcanology of Game of Thrones?

Spoiler alert: dragons didn't forge it.

Obsidian is real. It’s a black, vitreous substance, one that’s extremely hard and brittle, which means it can be used to form blades, arrowheads and spearheads. In fact, obsidian weaponry has been found all over the world dating back hundreds of thousands of years. It’s volcanic glass, essentially – but with a twist.

Normally, when small blebs of lava ejected from an explosive volcanic eruption fly through the air, they cool incredibly quickly below something called the glass transition temperature. This rapid cooling doesn’t allow the molecular structure of the silica-based liquid to properly rearrange itself into something more stable, and instead it turns into a genuine glass – one that’s often tear shaped.

Obsidian is different. Although it’s still a type of glass, it’s only associated with an incredibly thick, viscous lava – one with a very high silica content.

Dragonglass, AKA obsidian. (Shutterstock)

This “felsic” lava is far less common than the more fluid types you tend to see at, for example, Hawaii’s continuously erupting Kilauea; it’s so gloopy that it traps plenty of gas, and only turns up in the most catastrophically explosive of eruptions. Sometimes, after the explosive decompression phase dies out, the less gassy parts of the felsic magma chamber are oozed out, much like the last bit of toothpaste in a tube.

When this lava flows, its margins cool far more quickly than the hotter cores. When there aren’t many crystals floating around in these margins, these margins chill so rapidly that they form obsidian glass.

There’s quite a lot of obsidian, or dragonglass, in the Game of Thrones TV series. In fact – spoiler alert! – Samwell Tarly discovers at the start of Season 7 that the Citadel is built atop of a massive cache of dragonglass, which at this point appears to be geological in origin, rather than just a store.

So therein lies the question: where did it all come from? Where are all the volcanoes in the world of Game of Thrones?

This recent dragonglass-based revelation came courtesy of some books that Sam stole from the restricted section of the Citadel’s library. Thanks to the efforts of someone on Reddit, the text on one of the key pages of the book reads as follows:

“The Valyrians were familiar with dragonglass long before they came to Westeros. They called it [some Valyrian words] which translates to ‘frozen fire’ in Valyrian, and eastern texts tell of how their dragons would thaw the stone with dragonflame until it became molten and malleable. The Valyrians then used it to build their strange monuments and buildings without seams and joints of our modern crafters.”

The Valyrians, as I’m sure plenty of you will know, belonged to a long-lost dominion named the Freehold. The capital city was, predictably, Valyria, and could be found in Essos, the easternmost and largest continent in the world. Dragons frequented the skies back then, and lived peacefully with the Valyrians, who ruled the region for around 5,000 years.

According to the books, volcanoes formed a major part of the geography of the capital city. Large, fiery mountains – stratovolcanoes, no doubt, much like Mount Fuji or Mount St. Helens loomed in the background, and rivers of lava streaked through the streets.

This is what the streets of Valyria would have looked like, I imagine. (RICHARD BOUHET/AFP/Getty... [+] Images)

Stratovolcanoes on Earth generally sit atop large magma chambers, and only ever erupt explosively. Lava flows are rare unless these volcanoes are sitting atop something called a mantle plume, an upwelling fountain of superheated rock that continuously melts the crust. This way, you can get both effusive flows and explosive eruptions. Examples on Earth include Sicily’s Mount Etna and the Democratic Republic of Congo’s Mount Nyiragongo.

Then, something called the Doom of Valyria took place. Although details are sparse, it appears to have involved a vast volcanic eruption, one which destroyed not just the city but the land around it.

I’m reliably informed that every hill for five hundred miles exploded – including the “Fourteen Fires” –  and ash, smoke and fire filled the air. Part of the ground collapsed into the ocean and created the Smoking Sea, a highly acidic body of water that still steams today. East of Valyria, Velos and Ghozai – both on the Isle of Cedars – were destroyed by a megatsunami.

So what the hell happened here?

I suspect it was an extremely large eruption of some kind, perhaps even a supereruption. A vast store of magma accumulated beneath a cauldron-shaped formation for thousands, perhaps millions of years. Eventually, the internal pressure became too much, the roof of the cauldron collapsed, and the magma violently depressurized out onto the surface.

At this point, enormous earthquakes would have sent powerful seismic waves towards the magma chambers of the stratovolcanoes dotted around the landscape. Although this doesn't seem to happen in real life, perhaps this epic shaking set these other volcanoes in Essos off too, causing them to break through the overlying rock and burst onto the surface. Unfathomable clouds of ash, terrifying pyroclastic flows and surges, lava bombs and lava flows would have annihilated the region.

The Smoking Sea, at the point of its creation? (Shutterstock)

This lava began pouring into the sea too, through the new fissures generated by the earthquakes. Parts of Essos fell into the ocean – creating the megatsunami – as hydrothermal vents driven by submarine magma chambers went into overdrive, boiling the water and killing anything that fell into it.

Although plenty of this lava was likely to be basaltic – a common lava type that dominates the geochemistry of supervolcanoes and shield volcanoes like Hawaii’s alike – some of this must have been felsic. That thick, viscous magma would have been responsible for those explosive stratovolcano eruptions, and it’s almost certain that any late-stage lava flows oozing out at the end cooled quickly and formed – you guessed it – dragonglass.

There were likely felsic volcanic eruptions long before the Doom of Valyria, and they’ll be plenty more in the future. Either way, this type of volcanic cataclysm is what’s required to form dragonglass.

The cache beneath the Citadel – and Dragonstone, out in Blackwater Bay – implies that, long ago, these lands was once volcanic fields that has since frozen over. Indeed, Dragonmont, the mountain behind Dragonstone, looks to me a lot like an extinct, or dormant, stratovolcano.

So there you have it: the volcanology of Game of Thrones. I’m sure there’s plenty I’ve missed, but if you feel the urge to hunt down some White Walkers, let me know. After all, what kind of volcanologist wouldn’t have his own personal supply of dragonglass?