In 1911, during an expedition to the McMurdo Dry Valleys of Antarctica, geologist Thomas Griffith Taylor discovered something strange: a glacier gushing blood-red water.

Decades later, researchers figured out that this waterfall owes its brilliant hue to iron oxide—basically rust. But they weren’t exactly sure where the red rivulet originated. In 2015 a team of scientists speculated that there was a system of underground waterways full of briny water flowing through the ice, Rachel Feltman reports for Popular Science. Now, in a follow-up study published last week in the Journal of Glaciology, the team has mapped the Taylor Glacier's innards, showing the path that water takes to Blood Falls and many other unusual features beneath the ice.

The researchers tracked the path of the briny water beneath the ice using radio-echo sounding, which is kind of like how a bat emits clicks or squeaks to navigate and find food in the dark. The researchers bounced short radio waves into the glacier. The waves bounced back from the ice and water at different speeds creating a map of the salty streams and reservoirs. Past research suggests that the water may have been trapped under the ice for 1 million years—part of a salty lake that was covered by the glacier.

They were able to trace the water that feeds Blood Falls from a reservoir in the glacier along a 300-foot path. Occasionally, cracks within the glacier open up, allowing the salty, iron-rich water to squirt through the crevasses from areas of higher pressure to lower pressure and eventually making their way to the falls. When the water hits the open air the iron in the water reacts with oxygen, producing the blood red pigment.

“We knew that there was a brine outflow creating the falls, and that 2015 paper pretty much verified that the salty water came from beneath the glacier,” Jessica Badgeley lead author of the study tells Feltman. “The mystery that remained was the link between that source and the outflow. This is an unusual feature, and there are very few things like it. So it wasn’t obvious how you got the brine from below the glacier up to the surface.”

The researchers also used a gadget called an IceMole to burrow through the glacier to the under-ice reservoir to make sure their readings were correct, Feltman reports.

Even more intriguing is the fact that liquid water can exist inside and beneath the frozen glacier at all. As University of Alaska, Fairbanks, glaciologist Erin Pettit explains in a press release: “While it sounds counterintuitive, water releases heat as it freezes, and that heat warms the surrounding colder ice.” In the intense cold under the glacier, enough of the brine freezes to releases enough heat to keep the remainder of the brine liquid. She also points out that the salt in the water lowers its freezing point also helping to keep it liquid. “Taylor Glacier is now the coldest-known glacier to have persistently flowing water,” she says.

That has implications for the movement of glaciers as climate change progresses. Badgeley tells Feltman that most glaciers with temperatures below freezing were assumed to have no flowing water. Now, due to this research some of the models of those glacier's activity need to be revisited. It also suggests that as glaciers warm up, water could flow inside and beneath more glaciers, imacting their every move.