They are giant ice sheets that form on the sea during prolonged temperatures below the freezing point. Harsh wind and strong waves break the ice sheets into smaller (albeit still big in relation to us) ice formations, which are then pushed towards shorelines, where they pile up
These American regions are prone to ice tsunamis:
The Great Lakes Region
New York and Ohio’s Lake Erie
Niagara Rive
https://energiesmedia.com/ice-tsunamis-shorelines-american-region-next/
