Geologic map of Mount Gareloi, Gareloi Island, Alaska

Scientific Investigations Map 3145
By: , and 



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.

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Geologic map of Mount Gareloi, Gareloi Island, Alaska
Series title Scientific Investigations Map
Series number 3145
DOI 10.3133/sim3145
Year Published 2012
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Alaska Volcano Observatory, Volcano Hazards Program
Description Pamphlet: ii, 18 p.; Appendix Download; Sheet: 30.93 x 29.64 inches; GIS Data Download
Country United States
State Alaska
Other Geospatial Mount Gareloi;Gareloi Island
Datum North American Datum of 1983
Projection Universal Transverse Mercator, Zone 1 North
Scale 24000
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details