Maug Islands

Geography & Climate

Maug Islands is located in United States, within the Mariana Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 20.02° N, 145.22° E in the Northern Hemisphere, the volcano lies within a tropical climate zone. At just 227 meters above sea level, Maug Islands is a relatively low-elevation volcanic feature. Despite its modest height, it remains an active geological formation with the same underlying magmatic processes as its taller counterparts. 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

Maug Islands 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 Maug Islands, 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.

GVP Reference Summary

The three small elongated Maug Islands, the largest ~2.3 km long, represent the rim of a 2.5-km-wide caldera on a submarine edifice more than 20 km in diameter. The caldera has an average submarine depth of about 200 m and contains a central lava dome that rises to within about 20 m of the ocean surface. The truncated inner walls of the caldera on all three islands expose lava flows and pyroclastic deposits that are cut by radial dikes; bedded ash deposits overlie the outer flanks of the islands. No eruptions are known since the islands were documented by Espinosa in 1522 CE. The presence of poorly developed coral reefs and coral on the central lava dome suggests a long period of general quiescence, although it does not exclude mild eruptions (Corwin, 1971). A 2003 NOAA expedition detected possible evidence of submarine geothermal activity.

— Smithsonian Institution, Global Volcanism Program