Glaciers are enormous rivers of ice that slowly move across the land, and sometimes a large piece breaks away and crashes into the sea. This is called "calving," and it can make a huge, rumbling roar followed by a big splash as the ice hits the water.
Did you know? When a piece of a glacier breaks off, it becomes an iceberg. Some icebergs in Antarctica are so large they can even be seen from space!
Tom Crean and his crewmates sometimes heard glaciers breaking from far away, the sound rolling across the ice like distant thunder before an enormous splash followed soon after.
Try It Yourself Can you make a rumbling sound like a glacier breaking? Try growling low in your throat, then clap your hands once for the splash at the end!