A couple named Rick and Wanda Stead were taking a video of an iceberg from a boat in the Bay of Exploits, Newfoundland, when the arch cracked and collapsed into the water.
Here's the video. Warning: There are a couple blood-curdling screams.
"I think my heart came up, and I swallowed it. I was petrified," Wanda Stead tells CBC. "All I could see was this tidal wave coming toward us."