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Glacier Bay National Park and Preserve

National park in Alaska, United States

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Through UNESCO, Man and the Biosphere Programme and Sedimentary rock

Glacier Bay became part of a binational UNESCO World Heritage Site in 1979, and was inscribed as a Biosphere Reserve in 1986. The National Park Service undertook an obligation to work with Hoonah and Yakutat Tlingit Native American organizations in the management of the protected area in 1994. The park and preserve cover a total of 3,223,384 acres (5,037 sq mi; 13,045 km2), with 2,770,000 acres (4,328 sq mi; 11,210 km2) being designated as a wilderness area.

Geology

The west side of the bay consists of a 26,000 feet thick sequence of Paleozoic sedimentary rocks, mainly massive limestones and argillite. The oldest rocks in this sequence are the Late Silurian Willoughby limestone and the youngest being the Middle Devonian Black Cap limestone. An outcrop west of Tidal Inlet includes a sandstone, graywacke and limestone of unknown age. Sedimentary rocks of unknown age on the east side of Muir Inlet include tuff interbedded with limestone. The rocks exposed on the 1,205 foot high hill called "The Nunatak" have been metamorphosed. Early Cretaceous diorite stocks are exposed south of Tidal Inlet, and on Sebree and Sturgress Islands. Quartz diorite outcrops on Lemesurier Island. A granitic stock is exposed in Dundas Bay. Mafic dikes up to 20 feet in width occur throughout the area.

Glacial advances occurred 7,000, 5,000 and 500 years ago, with the last extending to the entrance of the bay, where it left a huge semicircular terminal moraine. The consequent surface glacial deposits include gravels as outwash and moraines. Glacial gravels extend up to 2000 feet up the mountain slopes. Lakes have formed where the glaciers have dammed the heads of valleys. Preglacial forests are found east of Goose Cove and on the east side of Muir Inlet. According to Rossman, "One of the outstanding features of the Glacier Bay area is the rapid advance and retreat of the glaciers during several substages within the last few thousand years."

A molybdenite deposit occurs on The Nunatak in quartz veins associated with a quartz monzonite porphyry, which includes gold at 0.04 ounces per ton, and silver at 7.07 ounces per ton. A copper deposit occurs on Observation Mountain. Quartz veins containing gold are exposed west of Dundas Bay and on Gilbert Island. Placer gold is also found in the bay. A silver deposit was mined on the western portion of Rendu Inlet.

According to MacKevett et al., "The most extensive and best gold placer deposits...are in the beach sands near Lituya Bay." Mining of these sands started in 1894, employing up to 200 men by 1896. However, most production had ended by 1917.

The granodiorite and quartz diorite area between Lamplugh Glacier and Reid Glacier contains most of the quartz vein gold lodes, which were produced by six mines. This is known as the Reid Inlet gold area. The Monarch Mines and the Incas Mine was discovered in 1924 by J. Ibach. The Monarch No. 1 and No. 2 veins were drift mined with 200 and 150 foot adits respectively. The LeRoy Mine was the largest, discovered in 1938 by Gustavus founder and resident A.L. Parker and his son L.F. Parker. They operated a two-stamp mill and an aerial tramway until most production had ceased by 1945.

The region experiences tectonic activity with frequent earthquakes. Earthquake-induced landslides have been significant forces for change, inducing tsunamis. Additionally, parts of the region are undergoing post-glacial rebound (also known as isostatic rebound), the process in which land rises after the weight of the glacier has been removed.

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