The Hawaiian archipelago is a chain of islands formed by a fixed plume of heat, known as a hotspot, beneath the moving Pacific tectonic plate. This process continuously feeds magma to the surface, forming massive shield volcanoes. The Big Island of Hawaiʻi sits directly over the hotspot and is home to the most active volcanoes.
The Most Recent Significant Eruption
The last significant volcanic activity occurred at Kīlauea, the most active volcano in the chain, with a series of short, intense eruptions beginning on December 23, 2024. This activity was confined to the volcano’s summit caldera, specifically within the Halemaʻumaʻu crater in Hawaiʻi Volcanoes National Park. The eruption was characterized by episodic bursts of lava fountaining that would begin, last for several hours, and then pause before resuming.
The initial episode began on the evening of December 23, with sustained fountaining. The Hawaiian Volcano Observatory (HVO) reported that fountains from the south vent reached estimated heights of up to 1,400 feet (425 meters). This eruption style is typical of Kīlauea’s summit activity following magma recharge.
The last specific fountaining event, designated as Episode 39, concluded in the early hours of December 24, 2024. After the fountaining stopped, the eruption entered a pause, though continuous volcanic gas emissions confirmed that the system remained active.
The Active Volcanoes of the Islands
The Big Island of Hawaiʻi is built from five main volcanoes, with activity concentrated in the youngest three: Kīlauea, Mauna Loa, and Hualālai. These three are considered active, meaning they have erupted within the last 10,000 years and are likely to erupt again. Mauna Loa, the largest volcano on Earth by volume, last erupted in 2022 and is a shield volcano.
The remaining two volcanoes on the Big Island, Mauna Kea and Kohala, represent later stages in the island’s volcanic life cycle. Mauna Kea is classified as dormant, having last erupted about 4,500 years ago, but is still expected to become active again in the future. Kohala, the most northerly volcano, is considered extinct and is no longer expected to erupt.
The submarine volcano Kamaʻehuakanaloa (formerly Lōʻihi Seamount) is located off the Big Island’s south coast. This seamount is the youngest volcano in the Hawaiian chain and is currently considered active, despite its summit being about 3,280 feet (1,000 meters) below the ocean surface. Although it has not been directly observed erupting, earthquake swarms confirm that magma is moving within its structure. Kamaʻehuakanaloa is predicted to continue growing until it eventually breaks the ocean surface.
Monitoring and Forecasting Volcanic Activity
The Hawaiian Volcano Observatory (HVO), a branch of the U.S. Geological Survey, employs a sophisticated network of instruments to monitor the volcanoes, providing data that allows for forecasting future events. One primary tool is the use of seismometers to detect earthquakes and a distinct signal called “eruptive tremor,” which are caused by magma moving through the rock beneath the surface. An increase in the number and magnitude of earthquakes is a common precursor to an eruption.
Scientists also rely heavily on geodetic instruments like Global Positioning System (GPS) receivers and tiltmeters to measure ground deformation. As magma accumulates beneath the surface, it causes the ground to swell or “inflate.” This ground deformation is a direct indicator of pressure building within the volcano’s plumbing system.
Monitoring the release of volcanic gases, particularly sulfur dioxide (SO2), provides another method for tracking magma movement. Elevated gas emission rates often accompany an eruption or a period of magma intrusion near the surface. By combining data from these diverse instruments—seismic activity, ground inflation, and gas emissions—scientists can identify the measurable changes that precede an eruption, allowing them to issue warnings and forecast potential future activity.