Sailors used to worry about falling off the edge of the world. Surely somewhere out there, it all simply stopped, and the only thing left to do would be to fall. But what if you discover that you’ve already fallen, and now you’re trying to get back up? That’s what sailing towards Hubbard Glacier feels like.

The glacier is up to 65 meters (213 feet) wide at its face and 50 meters (164 feet) tall, but that’s only the tiniest piece of the ice: The main channel of this frozen river begins 122 kilometers (76 miles) back, pouring down from around the 3,400-meter (11,100-foot) mark off the shoulder of Mt. Walsh.

Hubbard is the longest tidewater glacier (meaning it ends at the ocean) in North America. But unlike nearly every other tidewater glacier on the continent, Hubbard is advancing, not retreating; it’s forever pushing a little further into the bay. Chunks of ice that break off become floaties for seals, who like the bergs because orca sonar doesn’t work well among them.

The deep blue of the face of the glacier on a sunny day—the color made by compression of ice crystals that can be a foot or more long—is the blue of the furthest stars. The glacier is on the move.