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Brandon L. Browne

Publications and source records attributed to Brandon L. Browne.

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Geologic map of Mount Gareloi, Gareloi Island, Alaska

Gareloi Island (lat 51.7° N., long 178.8° W.) is located in the Delarof Islands group of the Aleutian Islands, approximately 2,000 km west-southwest of Anchorage and 150 km west of Adak, the westernmost town in Alaska. This small (~8- x 10-km diam), uninhabited island is constructed exclusively of eruptive products from Mount Gareloi volcano, a Pleistocene and Holocene, steep-sided, composite stratocone that rises 1,573 m (5,161 ft) above sea level (asl). Mount Gareloi has been one of the most active Aleutian volcanoes since its discovery by the Bering expedition in the 1740s, though, because of its remote location, detailed observations of eruptive activity have been scant. As part of an effort to both monitor and study all historically active volcanoes in Alaska, the Alaska Volcano Observatory (AVO) undertook a field program at Mount Gareloi in the summer of 2003. During a month-long period, seismic networks were installed at Mount Gareloi and the neighboring Tanaga volcanic cluster. During this time, we undertook the first geologic field study of the volcano since Robert Coats visited Gareloi Island for four days in 1946. Understanding the geology of this relatively small island is important from a hazards perspective, because Mount Gareloi lies beneath a heavily trafficked air route between North America and Asia and has frequently erupted airborne ash since 1760. At least two landslides from the island have deposited debris on the sea floor; thus, landslide-generated tsunamis are also a potential hazard. Since seismic instruments were installed in 2003, they have detected small but consistent seismic signals from beneath Mount Gareloi's edifice, suggesting an active hydrothermal system. Mount Gareloi is also important from the standpoint of understanding subduction-related volcanism, because it lies in the western portion of the volcanically active arc, where subduction is oblique to the arc front. Understanding the compositional evolution of Mount Gareloi fills a spatial gap in along-arc studies.

Alaska

Preliminary volcano-hazard assessment for the Tanaga volcanic cluster, Tanaga Island, Alaska

Summary of Volcano Hazards at Tanaga Volcanic Cluster The Tanaga volcanic cluster lies on the northwest part of Tanaga Island, about 100 kilometers west of Adak, Alaska, and 2,025 kilometers southwest of Anchorage, Alaska. The cluster consists of three volcanoes-from west to east, they are Sajaka, Tanaga, and Takawangha. All three volcanoes have erupted in the last 1,000 years, producing lava flows and tephra (ash) deposits. A much less frequent, but potentially more hazardous phenomenon, is volcanic edifice collapse into the sea, which likely happens only on a timescale of every few thousands of years, at most. Parts of the volcanic bedrock near Takawangha have been altered by hydrothermal activity and are prone to slope failure, but such events only present a local hazard. Given the volcanic cluster's remote location, the primary hazard from the Tanaga volcanoes is airborne ash that could affect aircraft. In this report, we summarize the major volcanic hazards associated with the Tanaga volcanic cluster.

Alaska