West Glacier Creek, Chinitna Bay

West Glacier Creek, Chinitna Bay

by | Dec 6, 2021

West Glacier Creek flows generally south-southeast for about 7 miles (11 km) to the north shore of Chinitna Bay, draining a watershed between the Chigmit Mountains and Mount Iliamna, about 83 miles (134 km) southwest of Kenai and 60 miles (97 km) west-northwest of Homer, Alaska. The Chigmit Mountains are a subrange of the northern Aleutian Range and include two prominent stratovolcanoes, Mount Redoubt with an elevation of 10,197 feet (3,108 m), which is the high point of the Aleutian Range, and Mount Iliamna with an elevation of 10,016 feet (3,052 m). The Chigmit Mountains are bordered to the north by the Tordrillo Mountains, and on the northwest by the Neacola Mountains. Cook Inlet marks the eastern boundary of the range, while on the west, the mountains merge into the hills and lowlands of Lake Clark National Park and Preserve. To the south and southwest, the mountains continue as the Aleutian Range into the Alaska Peninsula. Chinitna Bay is situated on the western shore of Cook Inlet, north of the Tilted Hills on the Iniskin Peninsula, and is about 14 miles (22 km) long and 3-4 miles wide. The head of the bay and most of the southern shore are private lands. Most of the northern shore of the bay, from the mouth at Cook Inlet to the west side of West Glacier Creek, is within Lake Clark National Park and Preserve. Lake Clark was proclaimed a national monument on December 1, 1978, by President Jimmy Carter, using his authority under the Antiquities Act. In 1980, Congress passed the Alaska National Interest Lands Conservation Act, which established the unit as a national park and preserve. It is named after Lake Clark, the largest lake in the southwest corner of the park. The park and preserve extend from Cook Inlet west across the Chigmit and Neacola Mountains on the northern end of the Aleutian Range, and into the Bristol Bay watershed. Large populations of brown bears are attracted to feed on the sedge meadows and spawning salmon along the coast. Bear watching is a popular activity in the park and especially in Chinitna Bay. There is no road access and visitors can only reach the park by boat or small aircraft, typically from Anchorage, Kenai, or from Homer which has the nearest airport on the Kenai Peninsula.

Two major tributaries feed West Glacier Creek, the most significant is Right Fork which starts at the terminus of Umbrella Glacier on the southwest flank of Mount Iliamna and flows for 4 miles (6.4 km) to the confluence with Left Fork. Left Fork starts at the terminus of Tongue Glacier on the west flank of Mount Iliamna and flows south for about 13 miles (21 km) before joining with Right Fork, where the combined discharge flows through a braided network of streams called West Glacier Creek. The area north of Chinitna Bay is dominated by the mass of Mount Iliamna that developed over older plutonic rocks of the Jurassic age and consists primarily of a stratified assemblage of andesite lava flows, and minor lahar, pyroclastic flow, and debris-avalanche deposits. Mount Iliamna is extensively glaciated with ten glaciers descending from the summit region. Tuxedni Glacier is the longest and extends north for about 16 miles (26 km). In 1946, the glacier terminated in the tide flats at the head of Tuxedni Bay and has since retreated 4.4 miles (7 km). Lateral Glacier flows generally northeast for 6 miles (10 km) and terminates 1.5 miles (2.4 km) from the Johnson River which flows southeast for 11 miles (18 km) to Cook Inlet. Red Glacier is the next largest, extending 9 miles (14.5 km) southeast and terminating about 6 miles (10 km) from Cook Inlet. Umbrella Glacier flows southwest for 6 miles (10 km) from an elevation of about 8,000 feet (2,438 m) to its terminus at Right Fork. The combined ice volume of these four ice streams is about 3.6 cubic miles (15 cu km). Rock avalanche debris covers the lower elevations of Red Glacier and Umbrella Glacier. On Umbrella Glacier a debris-avalanche deposit covers an area of about 247 acres (100 ha) along the northwest side of the glacier with an estimated volume of 529 million cubic feet (15 million cubic meters). Avalanche deposits consist of unsorted accumulations of boulder and cobble gravel with a matrix of very poorly sorted sediments ranging from sand to pebble.

Rock avalanches on Umbrella Glacier were seismically recorded on February 9 and September 8, 2004. Both avalanches originated above Umbrella Glacier on the southwest flank of Mount Iliamna in a zone of hydrothermally altered rock covered by ice. The resulting failures occurred at elevations of about 7,874 and 8,366 feet (2,400 and 2,550 m) respectively, and both went down to bedrock. Reconstruction of the February avalanche using high-resolution satellite imagery taken within days after the event yielded an estimated volume of 88-177 million cubic feet (2.5-5 million cubic meters) with constant snow and ice erosion and deposition along the 4.1 miles (6.6 km) long flow path. The failure of the September avalanche was likely related to the de-butressed glacial headwall after the February avalanche. The significant volume of sediment introduced by the rock avalanches to the glacier surface will insulate the glacier from rapid melting and will likely increase the volume of suspended sediments in the Right Fork and subsequently West Glacier Creek. The sediment load carried by these streams will be deposited at the river mouth causing aggradation of the broad alluvial fan and potentially creating additional salt marsh habitat. Salt marshes are important habitats for brown bears, seabirds, invertebrates, and juvenile salmon. However, being located at the interface of land and sea, they are extremely dynamic ecosystems due to changing topography by sedimentation, tectonic uplift, erosion, stream hydrodynamics, tidal fluctuations, and storm surges. Read more here and here. Explore more of West Glacier Creek and Chinitna Bay here:

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This ‘warming stripe’ graphic is a visual representation of the change in global temperature from 1850 (top) to 2021 (bottom). Each stripe represents the average global temperature for one year. The average temperature from 1971-2000 is set as the boundary between blue and red. The color scale goes from -0.7°C to +0.7°C. The data are from the UK Met Office HadCRUT4.6 dataset. 

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