Fortification Bluff, Kamishak Bay

Fortification Bluff, Kamishak Bay

by | Feb 3, 2022

Fortification Bluff is a sea cliff over 3 miles (4.8 km) long that rises almost vertically to 1,200 feet (366 m), on the south face of Step Mountain in Kamishak Bay, about 125 miles (201 km) northwest of Kodiak and 82 miles (132 km) west-southwest of Homer, Alaska. The bluffs were named in 1914 by the U.S. Coast and Geodetic Survey for the imposing fortress-like appearance of the rock cliffs. Kamishak Bay is 30 miles (48 km) wide and situated on the southwest shore of Cook Inlet. The name is a transliteration from the Alutiiq by early Russians and was first published in 1826 as ‘Kamyshatskaya Bay’ by Gavril Sarychev. The rock of Fortification Bluff is mostly sandstone and siltstone of the Jurassic Naknek Formation. Alaska is a collage of imported rocks called terranes, which are pieces of the earth’s crust that were transported on different tectonic plates and accreted to the North American Plate. Most of Alaska consists of pieces of terranes that arrived from elsewhere. For example, the Alaska Peninsula is underlain by the Peninsular terrane, which is thought to have originated far south in the Pacific Ocean. The Bruin Bay Fault uplifted the rocks of this terrane, which were subsequently eroded and deposited into an adjacent basin, and then eventually lithified forming the Naknek Formation. The Naknek Formation consists of 30 different member units, mostly of sandstone, conglomerate, and siltstone. The rock belt extends from the southwest end of the Alaska Peninsula to southcentral Alaska. The combined thickness exceeds 9,842 feet (3,000 m), although the average thickness of the formation is more typically 5,577-6,562 feet(1,700-2,000 m). The member unit exposed at Fortification Bluff is called the Snug Harbor Siltstone, which consists mostly of dark-gray to black siltstone. The fine sediments of this unit were deposited in moderately deep ocean water, deeper than the base of wave oscillations and shallower than the carbonate compensation depth, in a basin having restricted circulation. Since the Last Glacial Maximum, the cliffs have retreated against the erosive forces of Cook Inlet waves. Intensive storms in lower Cook Inlet create large waves that impact the cliffs with enough force to cause significant erosion. Wave-cut platforms form when destructive waves hit a cliff face causing an undercut or wave-cut notch between the high and low watermarks, mainly as a result of abrasion, corrosion, and hydraulic action. Waves undermine the cliff until the overhanging weight causes a collapse, resulting in the cliff retreating landward. The base of the cliff forms a wave-cut platform as attrition causes the collapsed material to be broken down into smaller pieces, while some cliff material may be washed into the sea. These extensive platforms make an ideal habitat for marine plants and invertebrates and the predators that consume them.

During the late prehistoric and historic periods, Dena’ina, Alutiiq, and Yup’ik people used Kamishak Bay to access several traditional portage routes connecting Iliamna Lake to Cook Inlet. Kamishak Bay was also an important hunting region for the Dena’ina. In 1794, Captain George Vancouver explored the area when navigation charts of that time showed ‘Bourdieus Bay’, but Vancouver never mentioned the name in his journals of the voyage, so the name may have originated with Captain George Dixon. Dixon and Vancouver both served on Captain James Cook’s third voyage in 1778 on the HMS Resolution. Dixon realized the commercial possibilities along the northwest coast of America and later became a partner in King George’s Sound Company to develop fur trade in British Columbia and Alaska. In September 1785, Dixon and fellow trader Nathaniel Portlock departed England with two ships on a three-year voyage. In the summers of 1786 and 1787, Dixon explored the shores of present-day British Columbia and the Gulf of Alaska coast including the Dixon Entrance of Cook Inlet and Kamishak Bay. In 1818, after Alexander A. Baranov of the Russian-American Company retired, the Russian post at Aleksandrovsk, at present-day Nanwalek, was downgraded to a one-man station and most of the structure was moved to the Nushagak River on Bristol Bay. In 1867, the Alaska Purchase transferred the territory from Russia to the U.S., and the Alaska Commercial Company took over the Russian trading posts. During the 1880s and 1890s, Yup’ik hunters from Bristol Bay migrated each spring to Kamishak Bay to hunt sea otters for the Alaska Commercial Company agent John W. Clark at Nushagak. Many otter hunting camps were spread out along the shores of Kamishak Bay from Augustine Island south to Cape Douglas. The hunters took the seal and otter pelts to the Alaska Commercial Company warehouse in Kachemak Bay at Seldovia.

The sea otter is the smallest marine mammal and the largest member of the weasel family. Sea otters forage in relatively shallow coastal waters, diving to the bottom to catch their prey and surface to eat their food. The dives generally last 1-2 minutes with a maximum of 5 minutes and can reach 250 feet (76 m). When surfacing with their prey, otters will roll onto their back and place the food on their chests. They eat using their front paws and will use tools, such as rocks to crack open shells. Their main prey includes sea urchins, crabs, clams, mussels, octopus, fish, and other marine invertebrates. Sea otters are keystone predators known for structuring nearshore marine ecosystems based on their prey selection. About 90 percent of the world’s sea otters live in coastal Alaska. Sea otters were hunted nearly to extinction in the late 1700s and 1800s for the maritime fur trade. Once commercial harvest ceased, sea otter numbers rebounded and they re-colonized much of their former range. The history of sea otters in Kamishak Bay is vague. Based on surveys, it appears that a small remnant population of sea otters remained in Kamishak Bay in the early 1900s. Because this population was centered around Augustine Island, most surveys of the area included only the shoreline of Augustine Island and perhaps Shaw Island and Cape Douglas. This population probably grew throughout the 1940s and 1950s, and by 1965, some range expansion to the south had occurred. Counts made between 1969 and 1971 indicated that there may have been an increase in numbers around Augustine Island and the waters immediately to the north and west and that there had been a substantial movement from around Cape Douglas to the south in the vicinity of Shakun Rocks. Most likely, densities in Kamishak Bay increased steadily through the 1960s then stabilized or declined slightly as animals emigrated to the southwest and possibly to the east across Cook Inlet to Kachemak Bay. By the 1990s, the population range extended from northern Kamishak Bay to Cape Nukshak in Shelikof Strait. Sea otters inhabiting the Alaska Peninsula coast between Cape Douglas and Cape Chiniak are probably part of the original Kamishak Bay population. Otters further south are probably part of the large population that is centered near Kujulik and Amber Bays in Aniakchak National Monument and Preserve. Today the southwest Alaska stock of sea otters extends more than 1,553 miles (2,500 km) from Cook Inlet to Attu Island in the western Aleutian Archipelago; however, this population declined substantially, perhaps as much as 90 percent, between about 1990 and 2015. The Marine Mammal Protection Act prohibits the commercial harvest of sea otters but allows Alaska Natives to hunt sea otters for subsistence and traditional crafts. Read more here and here. Explore more of Fortification Bluff and Kamishak Bay 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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