Haleakalā is the massive shield volcano that forms the eastern portion of Maui, rising over 10,000 feet above sea level. While the volcano appears quiet, scientists classify it as dormant, meaning its eruptive cycle is not finished. Understanding the duration of this quiet period and the potential for future activity is an ongoing matter of public interest for residents and visitors.
The Last Known Eruption
The duration of Haleakalā’s dormancy is determined by the date of its most recent lava flow. Modern scientific analysis confirms the last eruption occurred sometime between 1480 and 1600 A.D. This means the volcano has been in its current quiet phase for over 400 years.
This final eruptive event occurred along the volcano’s Southwest Rift Zone, a prominent fracture system that extends from the summit region down to the coast. The eruption produced the flows known as the Kalua o Lapa flow, which formed the rugged, young landmasses around the Ahihi Kina`u and La Perouse Bay area in South Maui. The lava is a specific type called ankaramite, a dark, dense basalt rich in the mineral clinopyroxene.
The most recent eruption was previously believed to have occurred around 1790 A.D., based on early historical maps and local accounts. Detailed geological studies and modern dating techniques have since revised this timeline, establishing a significantly older age for the lava flows. The physical evidence remains fresh, contributing to its classification as a long-term hazard.
Defining Volcanic Status
Haleakalā is formally classified as a dormant volcano, a designation that sits between “active” and “extinct.” The United States Geological Survey (USGS) Hawaiian Volcano Observatory (HVO) defines an active volcano as one that has erupted in the last 10,000 years and is likely to erupt again. Haleakalā fits this description, having erupted at least ten times in the last 1,000 years.
A dormant volcano is not currently erupting but is expected to erupt again in the future. An extinct volcano is highly unlikely to erupt ever again because its magma supply has been completely cut off. Haleakalā is not extinct because its plumbing system remains intact and connected to the underlying hot spot that feeds the Hawaiian chain.
The volcano is currently monitored with a “NORMAL” alert level, which is the lowest status and indicates it is in a non-eruptive state. This status reflects the quiet period of centuries, but the potential for future activity remains a factor in hazard planning. The HVO considers Haleakalā a moderate-threat volcano based on its eruptive history and proximity to populated areas.
Methods Used to Date Eruption Events
The precise age of Haleakalā’s most recent flows was determined primarily through radiocarbon dating (Carbon-14 dating). This technique measures the decay of the radioactive isotope carbon-14 in organic materials, such as plants and trees, that were incinerated and sealed beneath the lava flows.
Scientists collect charcoal from beneath the lava flows, such as those near La Perouse Bay, to analyze the amount of remaining carbon-14. This process provides a reliable age for the plant material, which in turn dates the moment the lava flow was emplaced.
The revised timeline was also supported by paleomagnetic analysis, which studies the direction of the Earth’s magnetic field recorded in the cooling lava. The magnetic signature of the flows did not match the known magnetic pole position for 1790, but aligned with pole positions from older flows. This combination of radiometric and magnetic evidence provided the scientific certainty needed to update the eruption history.
Assessing the Probability of Future Activity
Although Haleakalā has been quiet for centuries, its long-term history indicates that the volcano will eventually erupt again. East Maui has seen at least ten separate eruptions over the past 1,000 years, establishing a clear pattern of intermittent activity. The typical recurrence interval for Haleakalā is estimated to be between 200 and 500 years.
The HVO uses a network of instruments to monitor the volcano for any signs of renewed magmatic movement. This network includes continuous GPS stations that detect subtle changes in ground elevation or shape, indicating magma movement beneath the surface. Seismometers also record seismic activity, looking for an increase in the number or strength of earthquakes that often precede an eruption.
A future eruption would most likely occur along the Southwest or East Rift Zones, following the pattern of past activity. Potential hazards include fast-moving lava flows that could impact coastal communities and infrastructure. Additionally, ashfall and volcanic gas, known as vog, could affect air quality and visibility across the island, even though shield volcano eruptions are generally non-explosive.