It's as eerie as it is breathtaking and surprising: a waterfall in Antarctica that runs blood-red. The appropriately named Blood Falls drops five stories from the Taylor Glacier and into Lake Bonney, its bright red hue like a wound through the glacier. The Smithsonian digs into the story behind the falls, which sit in the McMurdo Dry Valley and are accessible only via cruise ship or helicopter. It is, of course, not blood that colors the falls, which CNN reports were discovered in 1911 by a geologist traveling with Robert Falcon Scott's expedition to the continent (the falls were not given Thomas Griffith Taylor's name, but the glacier was).
Algae was originally thought to be the source of the hue, notes Atlas Obscura; iron has since been identified as the culprit. But the story is much more intricate: Some 2 million years ago, glaciers covered what was a salty lake in East Antarctica, effectively creating an "aqueous time capsule" roughly 1,300 feet underground. The water collected there is much too salty to freeze, has no interaction with the atmosphere, and is oxygen-less. When it makes its way out of a fissure in the glacier, the iron-filled water finally greets the air, and "rusts," coloring the ice blood red as it falls. Wilder still: The lake—three times saltier than the sea, completely dark, and lacking oxygen—sustains microbes. (Another wonder in Antarctica: an even deeper "Grand Canyon.")