Wall of apocalyptic-looking 'sea smoke' appears over Lake Superior harbor | MLive.com:
"DULUTH, MINNESOTA - An ominous wall of fog that would rival something out of a Hollywood disaster film appeared near a Lake Superior port earlier this week.
In a short vide captured by Minnesota photographer Levi Drevlow, a freighter can be seen moving through the Great Lakes harbor in Duluth, Minn. on Wednesday, Dec. 21. In the distance, a massive wall of cloud-like matter can be seen.
And while it looks like something similar to the end of days, it's actually a naturally-occurring phenomenon known as "sea smoke." The same effect occurred in January."