Rauðibotn – lit. red bottom – is among the swarm of craters along the gigantic Eldgjá fissure in the Highlands of Iceland. It is connected to the currently active Katla volcanic system centred under the Mýrdalsjökull glacier.
Said to be the largest uninterrupted volcanic canyon in the world, Eldgjá came to be in the 934 AD eruption that produced one of the most prodigious lava flows ever recorded.
These following images were taken in 2014 from a Cessna 207 flight.
PS: See this later post for a second take.