Game of Thrones season 7 is in full swing, and one of the biggest stars has been the show’s geology. Daenerys has returned to Westeros to her family’s former home of Dragonstone, the castle that Stannis had occupied in previous seasons, and we’ve had several glimpses of the castle, the throne, and the surrounding areas that we hadn’t seen before.

View of the beach and the castle (digitally added) in the background. (Season 7, Episode 1)

The beach that Daenerys arrives on is a place I am actually rather well acquainted with — I did much of my PhD research there! The location is Itzurun Beach in Zumaia, Spain. The beach is actually a national park and it is known to geologists all over the planet.

Landing on the beach (Season 7, Epsiode 1)

Similar shot I took along the rock wall looking out towards the sea.

A view of the turbidite deposits in the flysch. (Season 7, Episode 1)

The landscape is so iconic that they even modeled the Dragonstone throne to match it. The rocks that we can see on the beach, which are the models for the throne, are deposits called “turbidites”. Turbidites are essentially underwater landslides. Sediment tumbles through the water, down underwater slopes, into deeper water, eventually settling out when the underwater landscape levels out.

An upclose view of some turbidite deposits, nearby to the filming beach location.

As the sediment tumbles through the water, the larger rocks travel faster and settle on the flat areas first, followed by slightly smaller rocks, and continuing down until the sand, silt, and clay are the last three layers. Each rock layer, that kind of looks like pages in a book, is the result of an individual landslide under the water. These turbidite “packages” are what is commonly known to European geologists as “flysch,” and there is even a store near that location with the name.

The Flysch store which is about a 5 minute walk from the beach where the filming took place.

In the most recent episode, we were treated with the discovery of “dragonglass”, which was in the cave that we got a glimpse of on the first episode.

A view outside the cave (Season 7, Episode 1)

Now, I can tell you from experience that the cave isn’t actually very big. It’s more like a hole in the rock. But besides that, you can’t have obsidian (the rock which “dragonglass” actually is) formed in the same environment or manner in which the turbidites are formed.

Walking into the “dragonstone” cave. (Season 7, Episode 4)

A reverse view of the previous shot into the cave.

As mentioned, turbidites are formed completely under water, usually in rather deep water. Obsidian on the other hand, is formed when lava from a volcano gets instantly cooled when it comes into contact with a body of water. You might be thinking, “But wait! There’s volcanoes on the bottom of the ocean; maybe those could produce obsidian.”

Unfortunately, those have the wrong type of lava to give us obsidian. You need lava from a volcano on the surface of the Earth. And even then, since the obsidian forms instantly when it comes into contact with water, it is impossible for obsidian to form the layers that are shown in the episode (however darkly they are shown).

A very dimly lit view of the “dragonglass” deposit. (Season 7, Episode 4)

So, sorry Jon. There is no dragonglass at Dragonstone.

Lava pouring into the ocean forming obsidian. From Weather.com

One side note. As everyone marches up the steps to the main gates of the castle, they come across a set of dragon heads.

Walking up the steps to the front gates of the castle. (Season 7, Episode 1)

View of the steps leading up to the palace gates, in real life.

Large dragon heads at the front of the castle. (Season 7, Episode 1)

View of the real life “dragon” statues at the top of those stairs.

I don’t know if the dragons on the show were inspired by the real life ones, but they are coincidentally in the exact same location.