Mauna Kea is the highest peak in the Hawaiian archipelago and one of the five shield volcanoes that form the Island of Hawaiʻi. Rising over 13,800 feet above sea level, it is not currently erupting, which often leads to questions about its status. Geologists definitively classify Mauna Kea as a dormant volcano. While its long period of quiet activity means it is not active in the immediate sense, its geological history confirms it is not extinct.
How Geologists Classify Volcanoes
Volcanologists utilize three primary terms to categorize a volcano’s activity level: active, dormant, and extinct. The Global Volcanism Program considers a volcano “active” if it has erupted within the last 10,000 years, which defines the Holocene epoch. This definition focuses on a geological timescale, acknowledging that a volcano can be quiet for centuries and still be capable of eruption.
A volcano is classified as “dormant” when it is not currently erupting but is expected to erupt again in the future. This classification applies to systems that retain a magma supply, even if thousands of years have passed since their last surface activity. The term “extinct” is reserved for volcanoes scientists believe will never erupt again, typically because their magma supply has solidified completely.
Mauna Kea’s History and Current Classification
Mauna Kea began its life approximately one million years ago, building the majority of its bulk during the shield stage. During this period, frequent eruptions produced low-viscosity basalt lava, creating a broad, gently sloping shield shape. The volcano transitioned into its quieter post-shield stage around 250,000 to 200,000 years ago as the magma supply rate from the underlying hotspot decreased.
The post-shield stage is characterized by lower eruption rates, a change in lava chemistry, and the formation of a steeper, more irregular topography. The lava produced during this phase is more viscous and contains more gas, leading to the creation of cinder cones and rubbly flows. This change in eruptive style signals an aging Hawaiian volcano moving past its rapid growth phase.
The most recent eruption of Mauna Kea occurred approximately 4,600 years ago. This event, which generated lava flows and cinder cones, falls within the 10,000-year window of the Holocene epoch. Because of this relatively recent activity in geological time, the volcano cannot be considered extinct.
Due to the long period of repose since that last event, scientists classify Mauna Kea as dormant. Its history shows an estimated recurrence interval of about 1,000 years over the last 10,000 years. This pattern indicates that future eruptions are possible, which is why the dormant status is maintained rather than being deemed extinct, a fate reserved for its neighbor, Kohala.
Current Monitoring and Reawakening Potential
The Hawaiian Volcano Observatory (HVO) monitors Mauna Kea to detect any subtle shifts in its subterranean activity. Although the volcano is currently quiet, HVO maintains a network of instruments to track its status, which is currently set to a “NORMAL” alert level. This ongoing surveillance is designed to identify early warning signs that would precede a reawakening.
Monitoring techniques include seismometers to track earthquake activity, which provides the most immediate indication of magma movement. Mauna Kea’s seismic activity is typically very low, characterized by small magnitude earthquakes representing background levels. A significant increase in the number or size of earthquakes, particularly those occurring in swarms or at shallow depths, would signal magma rising into the volcanic plumbing system.
Ground deformation is another measurement, monitored using Global Positioning System (GPS) receivers and tiltmeters. These instruments are sensitive enough to measure minute changes in the volcano’s shape, such as ground inflation caused by the pressurization of a subsurface magma chamber. Mauna Kea is monitored by a continuous GPS instrument and three seismometers directly on the volcano, supplemented by equipment on adjacent volcanoes.
While Mauna Kea’s risk is currently low, a clear signal of potential reawakening would be a simultaneous change across multiple data sets. For instance, ground inflation detected by GPS coinciding with an increase in seismic swarms would prompt scientists to raise the alert level. These combined signals indicate that new magma is recharging the system and moving toward the surface, making the prediction of a future eruption possible.