Mauna Loa, the massive shield volcano that dominates the Big Island of Hawaii, is an active geological force. The question of whether this mountain is currently active requires looking at its behavior over different timescales, its structure, and the ongoing monitoring conducted by volcanologists. The simple answer is yes, Mauna Loa is classified as an active volcano, but understanding what that means involves exploring its recent history and the mechanics of its eruption cycles.
Defining an Active Volcano
In the context of volcanology, an active volcano is one that has erupted within the last 10,000 years. By this definition, Mauna Loa is unquestionably active, with its last eruption occurring in 1984. This places it firmly within the Holocene epoch of active volcanism. The designation also implies that the volcano possesses a magma chamber capable of generating molten rock and that it has the potential to erupt again in the future. While the 1984 event was relatively gentle, the long-term history of Mauna Loa is written in layers of fluid lava flows that have repeatedly reshaped the island.
Recent Eruptive History and Current Status
The 1984 Eruption
The most recent eruption of Mauna Loa occurred in March 1984, sending lava flows toward the city of Hilo. This event, while disruptive, provided scientists with a crucial opportunity to study the volcano’s mechanics in real-time. The eruption began with a series of fissures on the northeast rift zone, and although the lava flows stalled just short of Hilo, it marked a significant reminder of the volcano’s capability. Since then, the volcano has experienced periods of inflation and deflation, signaling the movement of magma beneath the surface without breaking the crust.
Current Monitoring and Unrest
Today, Mauna Loa is closely watched by the United States Geological Survey (USGS) and the Hawaiian Volcano Observatory. The volcano is currently in a state of heightened unrest, characterized by increased earthquake activity and ground swelling. These signs indicate that magma is accumulating in the subsurface, pressurizing the rock above. While this does not guarantee an imminent eruption, it keeps the scientific community alert. The monitoring network includes GPS stations, tiltmeters, and gas sensors, all working to detect the subtle shifts that precede an eruption.
The Geological Engine of Mauna Loa
Unlike explosive stratovolcanoes, Mauna Loa is a shield volcano, built by the steady accumulation of highly fluid basaltic lava. This low-viscosity magma allows gases to escape relatively easily, leading to less violent eruptions characterized by fire fountains and extensive lava flows. The source of this heat is the Hawaiian hotspot, a plume of magma rising from deep within the Earth's mantle. As the Pacific tectonic plate slowly moves over this fixed point, it creates the chain of islands and seamounts, with Mauna Loa being the most recent and largest structure to form.
Hazards and Preparedness
The primary hazard posed by Mauna Loa is the rapid advancement of its lava flows. Because the lava is thin and runny, it can travel long distances quickly, particularly when confined to established rift zones or valleys. While the current population centers are generally protected by topographical features, the potential for flows to reach infrastructure remains a serious concern. Emergency management agencies on the Big Island regularly conduct drills and maintain evacuation plans based on the volcano’s behavior. Understanding the difference between a summit eruption and a rift zone eruption is critical for predicting the path of any future lava.
