Mount Westdahl, Unimak Island

Mount Westdahl, Unimak Island

by | Jan 10, 2022

Mount Westdahl, also known as Westdahl Peak, is a relatively young glacier-capped volcano with a summit elevation of 5,118 feet (1,560 m), located at the southwest end of Unimak Island in the eastern Aleutian Islands, about 527 miles (848 km) southwest of Kodiak and 87 miles (140 km) northeast of Dutch Harbor, Alaska. The volcano was named by O.H. Tittmann in 1902 for Ferdinand Westdahl of the U.S. Coast and Geodetic Survey, who determined its geographic position in 1901. Westdahl Peak is one of four summit peaks including Faris Peak, Pogromni, and Pogromni’s Sister. Pogromni is the highest with a summit elevation of 6,531 feet (1991 m), and there are five unnamed cinder cones nearby. The name comes from the Russian word meaning ‘violent outbreak’. The most active summit peak is Westdahl, located on a gently sloping plateau that may represent the surface of a truncated ancestral cone, composed of a thick sequence of basalt lava flows of Pleistocene age or older. The northeast-facing slopes are steeper, and the entire ancestral cone has been extensively dissected by erosion created by over 50 streams that radiate from the summit. The base of the cone has a diameter of 11 miles (18 km) and the size makes this one of the largest volcanoes in the Aleutian Islands, resulting in some volcanologists classifying Westdahl as a shield volcano. However, stratovolcanos are more common at subduction zones such as the adjacent Aleutian Trench, forming chains and clusters along plate tectonic boundaries where oceanic crust is drawn under continental crust. The magma forming stratovolcanoes rises when water trapped both in hydrated minerals and in the porous basalt rock of the upper oceanic crust is released into mantle rock above the sinking oceanic slab. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions. The lava flowing from stratovolcanoes typically cools and hardens before spreading far due to high viscosity.

Documented eruptions at or near Westdahl Peak occurred in 1795, 1796, 1820, and 1827–1830, but during that historical period, other eruptions might have gone undetected, given the volcano’s remote location and persistent cloud cover. Ivan Popov-Veniaminov described an eruption in 1795 on the southwest end of Unimak Island, which most likely occurred at Westdahl. Four eruptions in the late 18th century and early 19th century were attributed to Pogromni, but later studies have indicated that Pogromni has not been active in the historical period, and the observed eruptions should probably be assigned to Westdahl. Westdahl was frequently active during the latter half of the 20th century, with documented eruptions in 1964–1965, 1978–1979, and 1991–1992. The volcanic explosivity index of these last three eruptions corresponds to a ‘moderate’ or ‘moderate-large’ explosive event with 13-1300 million cubic yards (10–1,000 million cubic meters) of erupted material. In March–April 1964, a fissure eruption produced lava flows on the east flank of Westdahl Peak. In 1978, a vulcanian eruption through glacier ice lasted about six days and produced a crater with a diameter of 0.9 miles (1.5 km) and a depth of 0.3 miles (0.5 km) near the 1964 vent. The eruption column reached a height of 6 miles (10 km) and an ash deposit of 7 inches (18 cm) thickness was observed 9 miles (15 km) southwest of the vent. Ash reputedly fell on a ship 621 miles (1,000 km) southeast of the volcano. The eruption also produced a lahar down the southwest flank of Westdahl Peak that reached the sea. In 1979, an eruption cloud from Westdahl over 5 miles (8 km) high and 31 miles (50 km) wide was captured by a satellite image; however, no activity was reported from the U.S. Coast Guard lighthouse station at Cape Sarichef less than 16 miles (25 km) from Westdahl, although that was the year the station was automated. In November 1991, pilots reported the beginning of a fissure eruption through the ice at Westdahl resulting in a lava flow approximately 1.9 miles (3 km) wide, 16-33 feet (5-10 m) thick, and about 5 miles (8 km) long extending down the northeast flank. Dramatic lava fountaining and phreatic activity produced ash plumes that rose 4 miles (7 km) in altitude, prompting the Federal Aviation Administration to divert air traffic. Most of the ash was narrowly confined and remained at lower altitudes, dissipating harmlessly over the Bering Sea, however, light ashfalls occurred on Unimak Island including the village of False Pass, located 55 miles (88 km) northeast of the vent.

The volcanos namesake, Ferdinand N. Westdahl, spent 52 years in U.S. Coast and Geodetic Survey on the Pacific Coast and Alaska, many of them in command of survey ships. He was born in 1843 in Visby, a medieval city on the island of Gotland, Sweden. In 1865, he had immigrated to the United States and was employed by the Western Union Telegraph in an effort to build the Russian-American Telegraph, also known as the Collins Overland Telegraph, a wired communication line from San Francisco, California through Canada and Russian America, to Moscow, Russia. Western Union Telegraph funded Perry M. Collins to survey and build the line. The Smithsonian Institution and the Chicago Academy of Sciences funded Robert Kennicott to explore the flora and fauna of Alaska for the first time, and who along with hundreds of men and highly qualified naturalists and botanists embarked on March 21, 1865 from San Francisco to Alaska on the barkentine Golden Gate under the command of Captain Charles M. Scammon. Ferdinand Westdahl, was the first officer of the Golden Gate. In the spring of 1866, because of his knowledge of astronomy and surveying, Westdahl was assigned to work under Captain William Ennis at Unalakleet. West­dahl prepared a journal that was sent to his father in Sweden and from which extracts were published serially in a local Visby community newspaper. Notes written by Westdahl describe the difficulty of the survey work. Kennicott died in the field in 1866 and was replaced by William Healey Dall. In 1867, a transatlantic cable was successfully completed leading to the abandonment of the trans-Russian effort. In spite of this economic failure, many regard aspects of the effort a success given the benefits of the exploration brought to the regions that were traversed. Westdahl was soon employed by the U.S. Coast and Geodetic Survey and eventually become the Assistant Superintendent, and commanded the steamer McArthur, engaged in surveying along the coast of Alaska from the south coast of Unimak Island and the Sanak Islands east to Montague Island and Prince William Sound. His accounts were published in the U.S. Coast and Geodetic Survey Annual Reports for 1901, 1902, and 1903, and the results were incorporated on Coast and Geodetic Survey Charts. A World War II Liberty ship built by Kaiser Permanente shipyards was named SS Ferdinand Westdahl, as well as a hydrographic survey ship. Read more here and here. Explore more of Westdahl 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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