Glacier Bay, Part 3

Rivers of Ice
A glacier is born high in the mountains, where the only precipitation that falls is snow, and the snow that falls does not melt. A slight depression on the mountainside catches this snow. Year after year, the snowflakes pile up. Soon the sheer weight of this vast accumulation presses down on itself. The snow compresses. The flakes change shape and fuse into ice. Eventually, the weight of the ice is too much for the depression to hold against gravity and the ice begins to flow downhill seeking equilibrium. Now that it’s moving, it’s a glacier.

Types of Glaciers
Glaciologists have identified different types of glaciers based on their characteristics. For example, a glacier that remains confined within valley walls is a valley glacier. If it flows out of the valley and spreads out, it’s a piedmont glacier. If it simply drops out of the valley, it’s a hanging glacier. But the type of glacier most folks in Glacier Bay are interested in is the type that ends in the sea: the tidewater glacier.


















Discovery of Glacier Bay
In 1794 the HMS Discovery under the command of Captain George Vancouver was forced to drop anchor in Cross Sound due to floating bergs in the area. Two smaller boats were sent to investigate, and the men reported a 5-mile long bay. The 60-mile bay that exists today was covered with ice 300 feet high and 5 miles wide. (Glaciers continue to recede here as well as in all other parts of the world.)

Naturalist John Muir saw the bay in 1879 and described it as an "icy wilderness unspeakably pure and sublime." In a dugout canoe, Muir explored a bay 48 miles long.

Glacier Bay Today
The Bay today contains 12 tidewater glaciers, 30 alpine glaciers, and at least a dozen unnamed glaciers flowing into arms of the bay.


Blue Ice?
Why is some glacier ice blue? Pressure is exerted on ice crystals during glacier formation, and as the crystals morph, they absorb longer light length and reflect back only shorter wavelengths, the blue end of the visible spectrum. Glaciers appear bluer on overcast days (and are reportedly easier to photograph!). Blue ice becomes white as it is exposed to oxygen.