Geology and Physiography of the Pribilof Islands
The Pribilof Islands are located approximately 250 miles (400 km) north of the Aleutian Arc on the southern edge of the Bering Sea shelf (57°N, 107°W). The islands formed via basaltic lava flows which erupted onto the Pribilof Ridge, a structural arch that trends north-northwest and parallels the shelf-break (Barth, 1956 ; Winer et al., 2004 ). The two largest, inhabited Pribilof islands include St. George and St. Paul.
The islands are considered part of the Bering Sea Basalt Province (BSBP), a group of ~ 15 late Cenozoic basaltic volcanic fields that are widely distributed in the Bering Sea region and along the western margins of mainland Alaska (Wirth et al., 2002 ; Winer et al., 2004 ). These types of volcanoes are commonly referred to as 'intraplate volcanoes' because they occur far from plate tectonic boundaries. In the case of the BSBP, volcanism occurs within the North American Plate, laterally distal from the boundary with the Pacific Plate to the south.
St. George Island is the older of the two principle Pribilof Islands. Radiometric dating of St. George lava flows yield ages of approximately 2.2—1.6 million years old (Cox et al., 1966 ). Lava flows on St. Paul Island are significantly younger and range in age from 540,000—3,230 years old (Winer et al., 2005 ). The ages of volcanism on Otter Island and Walrus Island, the two smallest, uninhabited Pribilof Islands, are currently unknown.
The topography of the islands ranges from smooth, sloping shield volcanoes like Bogoslof Hill (St. Paul Island) to steep, highly-eroded vertical cliffs like the High Bluffs (St. George Island).
To further investigate the geology and physiography of the Pribilof Islands, check out the links below:
Geology of the Pribilofs
Resources containing information about the geology of the Pribilof Islands, Alaska.
- Alaska Volcano Observatory. This website contains general information about the location and activity of volcanoes in Alaska, including St. Paul and St. George Islands. (more info)
- Geology and Petrology of the Pribilof Islands, Alaska. [Barth, 1956] This U.S. Geological Survey Bulletin paper discusses the general geology of the Pribilof Islands. Many figures accompany the text, including geologic maps and stratigraphic columns of St. Paul and St. George. (citation and description)
- Geomagnetic Polarity Epochs; Pribilof Islands, Alaska. [Cox et al., 1966] This paper compares geologic, radiometric, and paleomagnetic methods of dating and stratigraphic correlation in the Pribilof Islands, Alaska. Detailed information on radiometric dating of basalts is included. Many figures accompany the text, including a geologic map of St. George Island. (citation and description)
- Evidence for Fractionation of Quaternary Basalts on St. Paul Island, Alaska, with Implications for the Development of Shallow Magma Chambers beneath Bering Sea Volcanoes. [Feeley and Winer, 1999] This paper discusses the composition of igneous rocks on St. Paul Island. Detailed information is provided about the geochemistry of extrusive igneous rocks on St. Paul. (citation and description)
- Basaltic Volcanism in the Bering Sea: Geochronology and Volcanic Evolution of St. Paul Island, Pribilof Islands, Alaska. [Winer et al., 2004] This paper discusses the volcanic history and evolution of St. Paul Island. Geologic information is provided about the tectonic setting of the Pribilof Islands, structural geology, and the timing and nature of volcanic activity on St. Paul. Many figures accompany the text, including a detailed geologic map of St. Paul. (citation and description)
- Evolution of Crust and Mantle Beneath the Bering Sea Region; Evidence from Xenoliths and Late Cenozoic Basalts. [Wirth et al., 2002] This paper describes late Cenozoic volcanic centers located throughout the Bering Sea region of Alaska. A very detailed discussion of the geochemistry of mantle xenoliths is provided along with several tables of data accompanying the text. (citation and description)
Geologic Maps of The Pribilofs
Resources containing geologic map information for the Pribilof Islands, Alaska.
- Alaska Volcano Observatory Geologic Maps of the Pribilofs. This resource contains generalized geologic maps of St. Paul Island and St. George Island, Alaska. (more info)
- Geologic Map of Alaska. This resource contains a generalized geologic map of Alaska provided by the Alaska Department of Natural Resources. (more info)
Physiography of the Pribilofs
Resources containing information about the physiography of the Pribilof Islands, Alaska.
- Mapping Ecologically Sensitive Islands in the Bering Sea. This USGS article provides an overview of mapping in the Pribilof Islands. External links lead to information about the Pribilof Islands Restoration Project. (more info)