Glaciers & Icebergs of Glacier Bay National Park
you enter Glacier Bay in Southeast Alaska you will cruise along shorelines completely
covered by ice just 200 years ago.
Explorer Captain George Vancouver found Icy
Strait choked with ice in 1794, and Glacier Bay was barely an indented glacier.
That glacier was more than 4000 ft. thick, up to 20 miles or more wide, and extended
more than 100 miles to the St.Elias Range of mountains.
By 1879 naturist John Muir found that the
ice had retreated 48 miles up the bay. By 1916 the Grand Pacific Glacier headed
Tarr inlet 65 miles from Glacier Bay's mouth. Such rapid retreat is known nowhere else on earth! Scientists have documented it, hoping to learn how glacial activity
relates to climate changes.
Glacier Bay National Park includes 16 tidewater
glaciers:12 actively calve icebergs into the bay. The show can be spectacular.
As water undermines the ice fronts, great blocks of ice up to 200 feet high break
loose and crash into the water.
The Johns Hopkins Glacier calves such volumes
of ice that it is seldom possible to approach its ice cliffs closer than about
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
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Glaciers form because the snowfall in the high
mountains exceeds snow-melt. 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, usually far less than 4 to 7 feet
per day. The point at which the rate of melt equals the rate of accumulation
is the glacier's terminus or snout.
If the glacier's snout reaches tidal waters,
we call it a tidewater glacier.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.
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
* If the world's ice caps thawed completely, sea level would rise enough
to inundate half the world's cities.
* The Greenland and Antarctic ice caps are 2 miles thick.
* Alaska is four percent ice.
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A Birthplace of Icebergs
As glaciers find the water's edge, the result of a long deliberate push towards the Glacier Bay, they "calve" in a thundering splash, releasing Icebergs large and small to the awaiting bay.
As kayakers pass by these floating giants, they have heard the stress and
strain of melting: water drips, air bubbles pop, and cracks develop.
icebergs may last a week or more before the finish there transition back to liquid water.
betray a berg's nature of origin. White bergs hold many trapped air bubbles.
Blue bergs are dense. Greenish-black bergs calved off of glacier bottoms. Dark-
striped brown bergs carry morainal rubble from the joining of tributory glaciers,
or other sources.
How high bergs- favored perches for bald
eagles, cormorants, and gulls- float depends on size, ice 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
Keep in mind that what you see is "just the tip of the iceberg."
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Glacier Bay Park
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Glacierbay.org works in tandem with its sister website www.gustavus.com...
Why? Because Gustavus IS the gateway to Glacier Bay National Park!
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