Gareloi

Geography & Climate

Gareloi is located in United States, within the Aleutian Ridge Volcanic Arc of the broader North America Volcanic Regions. Situated at 51.79° N, 178.79° W in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 1,573 meters above sea level, Gareloi is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Gareloi sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in United States near Gareloi, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is basalt / picro-basalt, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Gareloi has 16 recorded eruptions in the geological database, spanning from 1760 CE to 1996 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1982 CE, reaching VEI 3 on the Volcanic Explosivity Index. Notable eruptions include 1982 CE (VEI 3), 1980 CE (VEI 3), 1929 CE (VEI 3). This level of eruptive frequency indicates a persistently active volcanic system that warrants ongoing monitoring. The most recent eruption in 1996 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 3, Gareloi has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel. With 16 recorded eruptions, Gareloi has a substantial eruptive history that provides valuable data for understanding volcanic behavior and assessing future hazards in the North America Volcanic Regions region. Given its recent activity, Gareloi is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

The 8 x 10 km Gareloi Island, the northernmost volcano of the Delarof Group at the western end of the Andreanof Islands, consists of a stratovolcano with two summits and a prominent SE-trending fissure. The fissure was formed during an eruption in 1929 and extends from the southern summit to the sea. Steep sea cliffs that are cut into rocks of an older, eroded center are found on the SW coast, and submarine deposits of three debris avalanches produced by edifice collapse are found offshore. Young lava flows cover the older volcano from the summit to the coast along three broad axes trending NW, ENE, and S. The 1929 eruption originated from 13 craters along a 4-km-long fissure. Phreatic explosions were followed by the ejection of glassy pumice, lapilli, scoria, and older blocks, as well as by the emission of four short, steep lava flows, one of which reached the SE coast.

— Smithsonian Institution, Global Volcanism Program