This wonderfully named natural phenomenon shows nature in one of its more destructive moods.
Brinicles, also known as ice stalactites, are possible because when ice forms, impurities in it are pushed out. In seawater, the main impurity is salt, and this causes a stream of supersaline water to descend downwards from the ice sheet above due to its increased density compared to the water around it. Salty water freezes at a lower temperature, which means this supersaline water is much colder than the water around it.
As this supercool, supersaline water descends, it brings about the formation of new ice below it, giving us the brinicle that you can see in the video below. When it reaches the sea floor… well, pray for the starfish.