Hubbard Glacier is the longest tidewater glacier on the North American Continent, at 76 miles from its source on Mount Logan in the Yukon Province of Canada to its face in Yakutat and Disenchantment bays in Alaska. The face of Hubbard is almost six miles in length, and has been advancing for about a century.

Every day massive blocks of ice 'calve' off the glacier and fall into the sea, forming icebergs that eventually flow out into Yakutat bay and thence to the open sea. This is an amazing sight to see, accompanied by a thunderous roar known locally as 'White Thunder'.

First, a sharp 'crack' is heard, followed by a low rumble as tons of ice and rock can be seen tumbling down the ice face into the sea, creating a small tidal wave and throwing up a cloud of debris and ice particles into the air, like a small explosion. The low rubble continues to echo around the bay, bouncing off the mountains.