Nothing at Gobustan is molten. The grey mud welling out of these cones is the temperature of the air, and what pushes it up is gas. There are twenty-odd of them on a cracked plain by the Caspian south of Baku, each a metre or three high with a crater of thick slurry in the top. If you stand five metres back from one, the surface swells into a dome, holds, then breaks with a wet plop as the bubble comes through. The interval is different at every vent. Between the cones lie broad soupy pools where the gas comes up in slow rings instead. Where mud has spilled and dried, the crust has shrunk into a mosaic of plates that crunch and tilt under your boots. The fresh flows are still grey-wet, the old ones curl at the edges, and each cone keeps the record of everything it has thrown out. The pressure behind all of it comes from a long way down, out of deep sediment squeezed hard enough to force clay, brine and stone up through solid rock.
Azerbaijan has more of these than anywhere else, roughly half the world's seven hundred, and the reason is the reason Baku exists. Where a mud volcano stands, oil usually lies far beneath it, and the early petroleum industry drilled where the ground was already spitting hydrocarbons. Each cone is a borehole that drills itself, carrying up fragments of the source rock. Planetary scientists come to these flows to read Mars, where landforms long taken for lava are now thought to be mud that erupted in much the same way. The cones at the far edge are only a few metres high, but from the lip you look out over the grey plain to the flat blue of the Caspian. The ones you walk among only gurgle. Elsewhere the same gas finds a spark and a cone becomes a tower of flame: one offshore in 2021 threw a fireball that was seen from Baku, seventy-odd kilometres away.