Incredible images of an unexplained and somewhat eerie zigzag pattern stretching for more than two kilometers (1.25 miles) on a frozen lake in Iceland has baffled locals, sparking theories on its source ranging from aliens to aquatic monsters. The bizarre markings on Lake Thingvallavatn in Thingvellir National Park were shared by the park's Facebook page earlier this month. The post reported that the unexplained pattern had been spotted by a nearby resident – a phenomenon apparently never seen in the area before. While Lake Thingvallavatn is generally covered in solid ice until spring, warmer winters over the last 15 years have resulted in it being only partially covered, and for shorter periods. Park official Einar AE Saemundsen noted that the striking linear patterns, which covered an area of more than two kilometers, hadn't formed in the same region as the other cracks in the ice, reported Lonely Planet.