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Glacier Bay

National Park & Preserve


cover of park brochure

park geology subheading
Silohuette of man standing in front of mountain range
Glacier Bay National Park & Preserve, Alaska

Tidewater Glaciers

Enter Glacier Bay and you cruise along shorelines completely covered by ice just 200 years ago.

Glaciers form when snowfall in the high mountains exceeds snowmelt. The snowflakes first change to granular snow -- round ice grains -- but the pressure from accumulating weight soon transforms the snow 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. Also on the west side of the park, the world's largest copper deposit can be found underneath the thick layer of ice.

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 four 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 really is "just the tip of the iceberg."

  • Explorer Captain George Vancouver found Icy Strait choked with ice in 1794, and Glacier Bay was a barely indented glacier. That glacier was more than 4,000 feet thick, up to 20 miles or more wide, and extended more than 100 miles to the St. Elias Range of mountains.

  • But by 1879 naturalist 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. Scientists have documented it, hoping to learn how glacial activity relates to climate change.

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.

Perhaps even more staggering is the rate at which some of the worlds glaciers are retreating. Many of the glaciers in Glacier Bay National Park and Preserve are exhibiting drastic retreat, mostly caused by climate change.

Glacier Bay National Park & Preserve, Alaska - Reid Glacier in 1899 - Gilbert #258
Glacier Bay National Park & Preserve, Alaska - Reid Glacier in 1899 - Gilbert #258
Glacier Bay National Park & Preserve, Alaska - Reid Glacier in 2003
Glacier Bay National Park & Preserve, Alaska - Reid Glacier in 2003

Glacier Bay National Park & Preserve, Alaska - Hoonah Glacier in 1931
Glacier Bay National Park & Preserve, Alaska - Hoonah Glacier in 1931
Glacier Bay National Park & Preserve, Alaska - Hoonah Glacier in 2003
Glacier Bay National Park & Preserve, Alaska - Hoonah Glacier in 2003


park maps subheading

The General park map handed out at the visitor center is available on the park's map webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

photo album subheading

A geology photo album for this park can be found here.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.

geologic research subheading

There has been over a century of research and scientist involvement at Glacier Bay, beginning well before the area’s incorporation into the National Park System. John Muir and Harry Fielding Reid began recorded observations of glacial processes in 1891. Pioneer ecologist William S. Cooper conducted studies of plant succession beginning in 1916, and along with eminent geologist W.O. Field was instrumental in the move to have the area protected as a national treasure. The Ecological Society of America originally lobbied for Glacier Bay to be set aside as a natural laboratory for studies of glaciology and associated biological and physical processes. When Glacier Bay National Monument was designated in 1925, the enabling legislation included an explicit recognition of the area’s value in providing "a unique opportunity for the scientific study of glacial behavior and of resulting movements and development of flora and fauna and of certain valuable relics of ancient interglacial forests…".

More information about the park's research program is available on the park's research webpage.

For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.

selected links subheading

NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

teacher feature subheading

General information about the park's education and intrepretive programs is available on the park's education webpage.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 01/04/2005  I   http://www.nature.nps.gov/Geology/parks/glba/index.cfm   I  Email: Webmaster
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