Mauna Loa

Geography & Climate

Mauna Loa is located in United States, within the Hawaiian-Emperor Hotspot Volcano Group of the broader Eastern Pacific Volcanic Regions. Situated at 19.48° N, 155.61° W in the Northern Hemisphere, the volcano lies within a tropical climate zone. Standing at 4,170 meters above sea level, Mauna Loa towers above the alpine zone, where vegetation gives way to bare rock, snow, and ice for much of the year. The high elevation means the upper slopes experience significantly colder temperatures than surrounding lowlands. The volcanic landform is characterized as a shield, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Mauna Loa is an intraplate volcano, meaning it formed away from any plate boundary. These volcanoes are often powered by hotspots — plumes of abnormally hot mantle material rising from deep within the Earth. Hotspot volcanoes like Mauna Loa tend to produce effusive eruptions with lava flows that can be relatively predictable, giving nearby communities in United States more time to prepare. However, they can also produce explosive phases, particularly when magma interacts with groundwater. 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

Mauna Loa has 111 recorded eruptions in the geological database, spanning from 8050 BCE to 2022 CE. The most powerful recorded event was an explosive event producing ash plumes up to several kilometers in 1868 CE, reaching VEI 2 on the Volcanic Explosivity Index. With an average interval of roughly 91 years between eruptions over a span of 10,072 years, this is one of the more frequently active volcanoes in the database. This persistent activity suggests a robust and well-supplied magma system beneath the volcano. With eruptive activity as recently as 2022 CE, Mauna Loa remains an actively monitored volcano.

Significance

Its 111 recorded eruptions make it one of the most prolific volcanoes in the entire global volcanic record, reflecting an exceptionally persistent magma supply system that has sustained near-continuous eruptive activity over millennia. Given its recent activity, Mauna Loa is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

Massive Mauna Loa is a basaltic shield volcano that rises almost 9 km from the ocean floor to form the world's largest Holocene volcano. Flank eruptions typically occur from the lengthy NE and SW rift zones, and from the Moku'aweoweo summit is caldera, which is within an older and larger 6 x 8 km caldera. Two of the youngest large debris avalanches documented in Hawaii traveled nearly 100 km from Mauna Loa; the second of the Alika avalanches was emplaced about 105,000 years ago (Moore et al., 1989). Almost 90% of the surface of the volcano is covered by lavas less than 4,000 years old (Lockwood and Lipman, 1987). Beginning about 1,500 years ago, a series of voluminous overflows from a summit lava lake covered about 25% of the volcano's surface. Over the last 750 years, from shortly after the formation of Moku'aweoweo caldera until the present, an additional 25% of the volcano has been covered with lava flows, mainly from summit and NW rift zone vents.

— Smithsonian Institution, Global Volcanism Program