What people most want when they see a glacier is to witness calving—the shearing off of ice in a dramatic crack. Such displays aren’t predictable, however: A glacier calves ice only when it feels like it, and not one moment before. But when it does, it’s a memorable experience, with chunks ranging from, say, the size of a TV set to the size of a house. The randomness of these events is the reason why the ship stays back, even if the channel seems clear: Strong calves can toss a boat around like a rubber ducky.
