Glacier Bay National Park

Glaciers
Gorp.com
Glacier Bay National Park
Glacier Bay National Park (courtesy, NPS)

Worldwide, the glacial facts are staggering. Glaciers and polar ice store more water than lakes and rivers, groundwater, and the atmosphere combined. Ten percent of our world is under ice today, equaling the percent being farmed. If the world's ice caps thawed completely, sea level would rise enough to inundate half of the world's cities. The Greenland and Antarctic ice caps are two miles thick. Alaska is four percent ice.

Glaciers form because snowfall in the high mountains exceeds snowmelt. The snowflakes first change to granular snow—round ice grains—but the accumulating weight soon presses it into solid ice. Eventually, gravity sets the ice mass flowing downslope at up to seven feet per day. The park includes some 12 tidewater glaciers that calve into the bay. The show can be spectacular. As water undermines some ice fronts, great blocks of ice up to 200 feet high break loose and crash into the water. Johns Hopkins Glacier calves such volumes of ice that it is seldom possible to approach its ice cliffs closer than about two miles. The glaciers seen here today are remnants of a general ice advance—the Little Ice Age—that began about 4,000 years ago. This advance in no way approached the extent of continental glaciation during Pleistocene time. The Little Ice Age reached its maximum extent here about 1750, when general melting began. Today's advance or retreat of a glacier snout reflects many factors: snowfall rate, topography, and climate trends. Glacial retreat continues today on the bay's east and southwest sides, but on its west side several glaciers are advancing.

The snowcapped Fairweather Range supplies ice to all glaciers on the peninsula separating Glacier Bay from the Gulf of Alaska. Mount Fairweather, the range's highest peak, stands at 15,320 feet. Near Johns Hopkins Inlet, several peaks rise from sea level to 6,520 feet within just 4 miles of shore. The great glaciers of the past carved these fjords, or drowned valleys, out of the mountains like great troughs. Landslides help widen the troughs as the glaciers remove the bedrock support on upper slopes.

Huge icebergs may last a week or more, and they provide perches for bald eagles, cormorants, and gulls. Close by, kayakers have heard the stress and strain of melting: water drips, air bubbles pop, and cracks develop. Colors betray a berg's nature or origin. White bergs hold many trapped air bubbles. Blue bergs are dense. Greenish-blackish bergs may have calved off glacier bottoms. Dark-striped brown bergs carry morainal rubble from the joining of tributary glaciers or other sources. How high a berg floats depends upon its size, the ice's density, and the water's density. Bergs may be weighed down, submerged even, by rock and rubble. A modest-looking berg may suddenly loom enormous—and endanger small craft—when it rolls over. Keep in mind that what you see is "just the tip of the iceberg."


Published: 29 Apr 2002 | Last Updated: 15 Sep 2010
Details mentioned in this article were accurate at the time of publication

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