Coghill River, Dartmouth Glacier

Coghill River, Dartmouth Glacier

by | Dec 27, 2021

Coghill River is in Chugach National Forest and flows southwest for 5 miles (8 km) from the terminus of Dartmouth Glacier to Coghill Lake, which is 4.7 miles (7.5 km) long, and then west-southwest for 3 miles (4.8 km) to College Fjord near Coghill Point, about 54 miles (87 km) west of Valdez and 32 miles (51 km) northeast of Whittier, Alaska. Dartmouth Glacier starts from the south flank of Mount Castner and flows southwest for 2.6 miles (4 km) to its terminus. Coghill River watershed is fed by several small cirque glaciers including Williams and Lafayette Glaciers as well as many snowfields on the western slope of the range separating Unakwik Inlet from College Fjord. Dartmouth and Williams Glaciers were named after Dartmouth College in Hanover, New Hampshire, and Williams College in Williamstown, Massachusetts in 1908 by a U.S. Geological Survey team of Ulysses S. Grant and Daniel F. Higgins who were both faculty at Northwestern University in Evanston, Illinois. Lafayette Glacier was named in 1947 by Douglas Brown of the American Geographical Society for Lafayette College in Easton, Pennsylvania. During the Last Glacial Maximum, Prince William Sound was covered by the Cordilleran ice sheet. When the ice sheet receded about 9,000 years ago, people began to migrate into the area, and evidence from a prehistoric village site called Uqciuvit about 10 miles (16 km) south-southwest of Coghill River suggests occupation from around 4,400 years ago. During the Little Ice Age, the mountain glaciers advanced and likely forced the abandonment of the village. The glaciers of College Fjord were first reported by Lieutenant Joseph Whidbey with Captain George Vancouver‘s survey party in 1794, followed by Samuel Applegate in 1887, Edward F. Glenn, Joseph C. Castner, and Walter C. Mendenhall in 1898, the Harriman Expedition in 1899, and the U.S. Geological Survey in 1908 and 1909. The most important of these visits were those by the Harriman Expedition and the U.S. Geological Survey. In 1899, Henry Gannett of the Harriman Expedition made a general map of College and Harriman Fjords showing the glaciers, and other members of the Harriman Expedition took many photographs while Gannett and Grove Karl Gilbert studied the glaciers as fully as their brief visit permitted. During several visits by the U.S. Geological Survey, Grant and Higgins took more photographs with detailed descriptions, and a more detailed map was made by Higgins that showed Coghill River, and Dartmouth and William Glaciers for the first time.

Grant and Higgins attached the name Coghill to the river, lake, and headland after William Hawes Coghill who performed assays on mineral collections for Grant. All three were faculty members at Northwestern Unversity and worked during the summer for the U.S. Geological Survey. Coghill did undergraduate work in mining and metallurgy at the Colorado School of Mines in Golden, Colorado, and received a degree in 1903. He took a teaching position at Northwestern University and also did research and assays for mining clients. He went on to earn a doctorate degree and worked for the U.S. Bureau of Mines, publishing many important papers on metallurgy. Coghill was not aware until late in life that several prominent geographic features in Prince William Sound had been named after him. Coghill Lake supports large numbers of sockeye salmon compared to other watersheds in Prince William Sound and historically produced the largest sockeye salmon returns within the local commercial fishery. The highest return of 1.1 million sockeye salmon occurred in 1982; however, in 1990 and 1991 the adult returns were below 10,000. Several hypotheses were proposed for the decline in wild sockeye salmon production and the most likely reason was a decrease in macro-zooplankton from excessive foraging by rearing fry in the lake. While the specific cause for the decline remains unknown, water sampling suggested that the lake is a nutrient-limited system that supports relatively low biomass of macro-zooplankton that are essential food for juvenile sockeye. A relatively common mitigation measure employed by Pacific Northwest fishery managers in these circumstances is to increase the zooplankton biomass to enhance juvenile sockeye survival. This is done by nutrient enrichment with the goal of promoting algal growth to feed a larger macro-zooplankton population. Nutrient enrichment is a proven technique to increase a lake’s capacity to produce zooplankton for rearing sockeye salmon which can result in greater smolt biomass, healthier out-migrating juvenile fish, and subsequently higher adult returns. In a trial of nutrient enrichment in Coghill Lake from 1993-1996, the seasonal mean phosphorous concentration of the lake increased 220%, and the abundance of zooplankton increased 117% compared to pre-enrichment years. The sockeye salmon smolt population increased from an average of 263,604 before enrichment to 940,411 during treatment.

The earliest recorded attempts to identify mineral resources in the region of present-day Chugach National Forest were made by Russian explorers in the mid-1800s. In 1848, Peter Doroshin, a mining engineer sent by the Russian-American Company reported finding widespread gold-bearing gravels along the Kenai River. In 1898, many prospectors originally bound for the Klondike goldfields were attracted by the gold discoveries in the Prince William Sound-Kenai Peninsula area. Evidence of historical mining, such as wing dams, hydraulic pipes, stamps mills, and workings, is common throughout the Chugach National Forest. Most of these operations were discontinued by the start of World War I. In 1934, there was a resurgence of mining activity when the price of gold rose, but activity decreased dramatically with the start of World War II. In the 1970s, a rise in the price of gold led to renewed placer mining activity and gold production, and between 1972-1982, there were approximately 35 gold placer operations in the Chugach National Forest ranging from small suction dredges and hand placer operations to large backhoe and dozer washing operations. A mineral resource inventory was conducted from 1979 to 1982 by the U.S. Geological Survey and the U.S. Bureau of Mines. The inventory was based on a literature search followed by a four-year field verification program. The literature search was made using historical files of the U.S. Geological Survey, U.S. Bureau of Mines, U.S. Forest Service, State of Alaska, and mining companies that were active in the area. Mining claim records were obtained from the Bureau of Land Management and the State of Alaska. Additional information was obtained from interviews and correspondence with miners and individuals knowledgeable about the geology, mining history, and mineral development of the area. The field verification program focused on areas that were recently exposed by retreating glaciers since these were not historically prospected. A highly mineralized zone was identified near Coghill Lake about 3 miles (5 km) below the terminus of Dartmouth Glacier. Field verification found gold in thin, poorly to moderately sorted alluvial gravels and concentrated on and in slate bedrock exposed in the canyon of the northwest fork of Coghill River. Three alluvium samples contained 0.0004 to 0.0063 ounces (0.0113-0.1792 g) of gold per cubic yard and gold nuggets up to 1/16 inch (1.6 mm) diameter were recovered. Read more here and here. Explore more of Coghill River and Dartmouth Glacier here:

About the background graphic

This ‘warming stripe’ graphic is a visual representation of the change in global temperature from 1850 (top) to 2022 (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. 

Credit: Professor Ed Hawkins (University of Reading). Click here for more information about the #warmingstripes.

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