Determining the world’s largest active volcano is complex because volcanic structures often have the majority of their bulk hidden beneath the ocean surface. Measuring only the elevation above sea level fails to capture the true scale of these giants. Determining the true size requires a holistic approach that accounts for the volcano’s entire mass and footprint. The agreed-upon winner is a massive structure whose size is best appreciated by considering its full geological volume and basal area.
Identifying the World’s Largest Active Volcano
The largest active volcano on Earth, measured by volume and area, is Mauna Loa, located on the Island of Hawaiʻi. Its name, meaning “Long Mountain” in Hawaiian, describes the immense size of this geological feature. Mauna Loa comprises over half of the surface area of the island, which is the largest landmass in the Hawaiian archipelago.
The designation of “active” means the volcano has erupted in the Holocene epoch, spanning the last 10,000 years, or shows signs of unrest. Mauna Loa’s last eruption in late 2022 confirmed its status as a currently restless volcano. This recent activity, combined with its physical dimensions, solidifies its position as the largest active volcano globally.
How Volcano Size is Measured
Volcanologists employ several distinct metrics to quantify a volcano’s size, which accounts for why different volcanoes may be cited as the largest. The most straightforward measurement is elevation above sea level, which quantifies the height of the summit from the nearest ocean surface. While this metric is easy to measure, it fails to capture the true scale of volcanoes that originate on the ocean floor.
A more comprehensive and geologically significant measure is total volume, which calculates the entire mass of the volcanic edifice from its base on the seafloor to its summit. This measurement is often expressed in cubic kilometers and provides an assessment of the amount of material erupted over the volcano’s lifetime. For volcanoes like those in Hawaii, this volume includes the vast, unseen portion resting on the ocean crust.
The third important metric is the basal area, or footprint, which measures the total area covered by the volcano at its base. This is a measure of the volcano’s horizontal extent. When volume and basal area are considered together, they provide the most accurate representation of a volcano’s magnitude and bulk.
The Unique Characteristics of this Giant
Mauna Loa is classified as a shield volcano, a type characterized by its broad, gently sloping profile resembling a warrior’s shield lying on the ground. This shape is a direct result of the composition and viscosity of the lava it erupts. The volcano is formed by hot, fluid, basaltic lava that flows easily and extensively before cooling, which builds up a wide, low-angle cone over millions of years.
The volcano is estimated to contain a volume of approximately 75,000 cubic kilometers of rock, establishing it as the most voluminous single mountain on Earth. Its true height rises about 9,170 meters (30,085 feet) from the seafloor to its summit. This measurement is considerably greater than the height of Mount Everest when measured from its base to its peak.
The structure formed above a stationary deep-mantle plume, known as the Hawaiian hotspot, which continuously supplies magma as the Pacific tectonic plate slowly drifts over it. This sustained, non-explosive, effusive eruptive style is responsible for the volcano’s immense size and gentle slopes. The low-viscosity lava flows can travel great distances from the summit or the volcano’s rift zones, contributing to its massive basal area. Its summit caldera, known as Mokuʻāweoweo, is a depression measuring approximately 3 by 5 kilometers across.
Eruption Cycles and Monitoring
Mauna Loa has a history of frequent activity, having erupted 34 times since written records began in 1843. Historically, the volcano has erupted on average once every five years, although the interval between eruptions has been highly irregular. Following the eruption of 1984, the volcano entered a period of quiescence that lasted nearly four decades, its longest stretch of inactivity on record.
The quiet period concluded with a summit eruption in late November 2022, which lasted for about two weeks before migrating to the Northeast Rift Zone. These eruptions are primarily characterized by rapid, high-volume lava flows that pose the main hazard to downslope communities. Unlike explosive stratovolcanoes, Mauna Loa’s hazards are not typically related to ash clouds or pyroclastic flows, but rather the speed and reach of its fluid lava.
The U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) maintains a robust monitoring network to watch for signs of unrest. This includes a dense array of seismometers that detect small earthquakes caused by magma movement beneath the surface. Scientists also use GPS and tiltmeters to measure ground deformation, which tracks the inflation of the volcano as magma accumulates in the shallow reservoir. Gas emissions, particularly sulfur dioxide, are also measured as an indicator of magma rising toward the surface, providing a multilayered approach to forecasting the giant’s next period of activity.