Scientists have just stumbled upon a truly amazing discovery in Antarctica, solving a huge mystery that has plagued scientific circles for more than 100 years. Antarctica’s famous “Blood Falls” were first discovered all the way back in 1911, but scientists had been unable to explain what caused the weird river of blood that flowed through one area and then spilled over a cliff into the sea. Now, however, one group of researchers think they have an explanation.

A study out of the University of Alaska Fairbanks claims that this blood red river is actually liquid rust. More specifically, it’s an iron-rich brine that is oxidizing as soon as it emerges from the depths deep below the glacier and makes contact with the oxygen in the air. It’s a far cry from the theory scientists had come up with before, which was that it was some kind of special algae.

This brine apparently comes from an incredibly salty lake that is trapped underneath the glacier. It is so salty, in fact, that it cannot freeze, and it is therefore able to scrape up iron from the bedrock, which then oozes out of the ice and into the open air.

“The salts in the brine made this discovery possible by amplifying contrast with the fresh glacier ice,” Lead author Jessica Badgeley said.

“We moved the antennae around the glacier in grid-like patterns so that we could ‘see’ what was underneath us inside the ice, kind of like a bat uses echolocation to ‘see’ things around it,” said co-author Christina Carr, a doctoral student at UAF.

“While it sounds counterintuitive, water releases heat as it freezes, and that heat warms the surrounding colder ice,” University of Alaska Fairbanks glaciologist Erin Pettit said. “Taylor Glacier is now the coldest known glacier to have persistently flowing water.”