Residents near Lake Thingvallavatn in southwestern Iceland woke up one day last week to discover bizarre patterns carved into the thin ice, something they've never seen before.
Thingvellir National Park posted photos of the symmetrical zigzags on its Facebook page last Thursday when they appeared, and explained that ice on Lake Thingvallavatn has not formed as solidly as in the past because of increasing temperatures, presumably allowing for the odd phenomenon.
"The linear and perpendicular pattern stretched more than 2km [1 1/4 miles] out into the lake," park official Einar AE Saemundsen told Lonely Planet. "The lines did not form in same area as other known cracks in the ice.
"Speculations started and there was no shortage of alternative explanations from alien activity and unknown monsters in the lake to strange conspiracy theories."
Here is some of wild speculation that appeared on the park's Facebook page:
"Drunk snowplow driver!"
"Can we get an aerial shot and see if this translates to a numeric barcode value?"
"An ice circle?"
While most made light of the bizarre patterns, one commenter apparently figured out what caused them, writing, "Classic `finger rafting.' Very cool phenomenon."
Saemundsen confirmed as much after speaking to experts and, thus, solved the mystery.
"Scientific explanations came from experts that recognized this as a very rare phenomenon called finger rafting," he told Lonely Planet. "But it is not known to have ever been seen before at Lake Thingvallavatn."
Lonely Planet explained the phenomenon like this: "Finger rafting occurs when thin ice sheets floating on water collide and push over and under each other alternately, creating what scientists describe as 'fingers.'"
Lake Thingvallavatn, the largest natural lake in Iceland, is one of the country's most famous landmarks, according to the Iceland Monitor. But it isn't likely to be known as the home of finger rafting anytime soon, unless these bizarre patterns start forming with regularity.