Mauna Kea is a colossal shield volcano rising 13,803 feet above sea level on the northern half of Hawai‘i Island. It is one of the five volcanoes forming the landmass and is internationally recognized as a premier site for astronomical observation. Understanding Mauna Kea’s eruptive history provides geological context for its current state and its potential for future activity.
Pinpointing the Last Eruption
The most recent activity on Mauna Kea occurred approximately 4,500 to 4,600 years ago, placing its last known eruption around 2600 BCE. This event marked the final phase of the volcano’s post-shield stage, producing flows and cinder cones known as the Laupāhoehoe Volcanics. This eruptive episode involved multiple outbreaks at various locations on the volcano’s flanks rather than being confined to a single vent.
Geologists determined this age using radiocarbon dating of organic material found buried beneath the most recent lava flows. Analyzing dated material, such as charcoal from the Humu‘ula soil layer, provided a minimum age for the overlying lava. This pinpointed the timing of the final eruptions, which created flows extending down the southern flank, including the Pu‘u Kole and Pu‘u Loa Loa lava fields.
Mauna Kea’s Current Volcanic Classification
Mauna Kea is formally classified as a dormant volcano, distinguishing it from the continuously erupting Kīlauea and the frequently active Mauna Loa. In Hawai‘i, a volcano is considered active if it has erupted in historical times, while an extinct volcano, like Kohala, is not expected to erupt again. Mauna Kea’s dormant classification reflects its extensive repose period while acknowledging its potential for renewed activity.
The volcano’s current status requires continuous, though less intensive, monitoring by the Hawaiian Volcano Observatory (HVO). Surveillance includes a network of instruments, such as GPS stations and seismometers, placed on the volcano and its surroundings. This equipment tracks ground deformation and seismic activity, which remain at low, background levels, indicating no immediate magmatic unrest. This low activity contrasts sharply with the frequent seismic swarms and ground inflation seen at the island’s more active volcanoes.
The Potential for Future Activity
Despite the extended period of quiet, Mauna Kea is expected to erupt again in the future. The volcano remains connected to the mantle plume and has entered a phase of deep repose typical of post-shield-stage Hawaiian volcanoes. The geological record indicates that Mauna Kea has a long history of lapsed activity, with breaks far longer than those seen at its younger neighbors.
Over the last 10,000 years, the volcano has exhibited an average recurrence interval of approximately 1,000 years between eruptive episodes. These events have been episodic rather than strictly periodic, meaning the volcano is not considered “overdue” for an eruption. When activity resumes, scientists predict it will likely occur on the upper flanks and produce long, slow-moving ‘a‘ā lava flows. These flows could potentially travel 9 to 16 miles from the vent, which is why the volcano retains the dormant classification.