This story was updated on October 22, 2018.

Blood Falls, named for its ruddy color, is not in fact a gush of blood from some unseen wound.

The color was initially chalked up to red algae, but a study in the Journal of Glaciology has uncovered its true origin using radar to scan the layers of ice from which the river pours.

The discovery came at the hands of a team of scientists, including National Geographic emerging explorer Erin C Pettit.

Located in Antarctica’s McMurdo Dry Valleys, the falls pour forth from Taylor Glacier, and the liquid bubbles up from fissures in the glacier’s surface. The flow was previously a mystery, as the mean temperature is 1.4 degrees Fahrenheit (-17 degrees Celsius) and little glacial melting can be seen at the surface.

Imaging from underneath the glacier helped solve the mystery, revealing a complex network of subglacial rivers and a subglacial lake—all filled with brine high in iron, giving the falls its reddish tint.

According to the study, the makeup of the brine explains the fact that it flows instead of freezes.

“The brine remains liquid within the subglacial and englacial environments through latent heat of freezing coupled with elevated salt content,” the study explains.

Iron-Filled, Salty Water

This diagram, a part of a study outlining the makeup of Taylor Glacier in Antarctica, shows how brine is injected into frozen and melting water to produce a red-brown waterfall. Diagram courtesy Cambridge University Press/Creative Commons

The lake under the glacier has an unusually salty consistency, and because saltwater has a lower freezing point than pure water and releases heat as it freezes, it melts the ice, enabling the rivers to flow.

This means that the glacier can support flowing water and also that this is the coldest glacier on Earth with constantly flowing water—though this water is so filled with iron that it looks like something else entirely.

The study also measured the amount of iron-rich brine in the river water and found the brine content increased as the measurements drew closer to the falls.

Water temperature and brine content were also found to be related: Cracks of various sizes in the glacier let brine into the glacier. Then the brine (pictured here in red to represent the amount of iron present in the water) begins to freeze, and the latent heat warms the ice around it, upping the brine concentration in the center of the cracks.