Kilauea erupts because it sits directly over a hotspot, a plume of exceptionally hot rock rising from deep within Earth’s mantle that continuously feeds magma upward through the Pacific Plate. This process has been building the Hawaiian Islands for tens of millions of years, and Kilauea, positioned at the southeastern tip of the Big Island, is currently the most active outlet for that heat. The volcano’s current eruption began on December 23, 2024, and has produced dozens of eruptive episodes at the summit through 2025, with lava fountaining from two vents inside Halemaʻumaʻu crater.
The Hawaiian Hotspot
In the 1960s, geophysicist J. Tuzo Wilson proposed that the Hawaiian island chain formed as the Pacific Plate drifted northwest over a stationary source of intense heat deep beneath the surface. This hotspot partially melts the rock in the overriding plate, generating magma that is lighter than the surrounding solid rock. That buoyancy drives it upward through the mantle and crust until it reaches the surface, either on the ocean floor or through an existing volcano.
The entire Hawaiian chain, stretching over 6,000 kilometers to include submerged seamounts called the Emperor Seamounts, is a record of this process. The islands get progressively older as you move northwest. Kauai’s rocks are roughly five million years old. The Big Island’s oldest exposed rocks are less than 700,000 years old, and new volcanic rock forms constantly. Kilauea, on the island’s southeastern flank, sits squarely over the hotspot today, giving it a nearly unlimited supply of fresh magma from below.
How Pressure Triggers an Eruption
A hotspot provides a long-term magma source, but individual eruptions are triggered by something more immediate: pressure buildup. Magma accumulates in reservoirs beneath Kilauea’s summit and along its rift zones, the long fracture systems extending from the summit. As more magma flows in from the mantle, pressure inside these reservoirs rises. The ground above physically swells, something scientists measure with tiltmeters and GPS stations positioned around the volcano.
The 2018 eruption illustrates this clearly. Starting in March of that year, instruments recorded rapid uplift at Puʻuʻōʻō, a vent on the middle East Rift Zone, followed weeks later by inflation at the summit. Lava lakes at both locations rose to unusually high levels, producing the largest overflows at Halemaʻumaʻu in over a decade. According to the USGS Hawaiian Volcano Observatory, magma pressurization was the driving force: rising pressure reached a critical threshold, and the magma could no longer be contained. The pattern, gradual pressure buildup followed by a sudden release, has repeated across many of Kilauea’s eruptions.
Summit Eruptions vs. Rift Zone Eruptions
Kilauea erupts in two general locations: at the summit caldera and along its East Rift Zone, a crack system running roughly 50 kilometers to the east. Summit eruptions tend to produce lava lakes and fountaining contained within the caldera. Rift zone eruptions can send lava much farther, sometimes reaching populated areas near the coast.
The 2018 lower East Rift Zone eruption was the largest in at least 200 years and the most destructive Hawaiian eruption in that same period. It partially drained the summit magma reservoir, which caused sections of the caldera floor to collapse. One reason this eruption was so large: the 2018 vents opened more than 900 meters (about 3,000 feet) lower in elevation than the summit, allowing gravity to help pull magma down through the rift system and out at high volume.
Since December 2020, eruptive activity has returned to the summit, inside Halemaʻumaʻu crater. The current eruption, which started in late December 2024, has followed this pattern as well, with all activity confined to the summit area.
The Current Eruption Pattern
The eruption that began on December 23, 2024, has been episodic rather than continuous. Lava fountains from two vents (one on the north side, one on the south) erupt for hours or days, then pause before starting again. Early episodes lasted anywhere from 14 hours to 8.5 days. By mid-2025, episodes had settled into a rhythm of roughly 6 to 13 hours of activity separated by pauses of one to three weeks. Through all of 2025, the USGS has recorded 39 distinct eruptive episodes.
The episodes have been gradually spacing out. In January and February 2025, new episodes arrived every 4 to 10 days. By the fall, the gaps stretched to two or three weeks. Each episode involves lava fountaining that fills portions of the crater floor, then the activity dies down as pressure temporarily drops in the shallow reservoir beneath the summit. The USGS currently maintains a volcano alert level of WATCH and an aviation color code of ORANGE, indicating elevated activity with potential hazards.
Sulfur Dioxide and Vog
Every eruption at Kilauea releases sulfur dioxide gas, which reacts with moisture and sunlight in the atmosphere to form volcanic smog, locally called vog. The amount of gas varies enormously depending on the eruption’s intensity and location. During the 2018 lower East Rift Zone eruption, a single fissure was emitting more than 50,000 tons of sulfur dioxide per day, creating severe air quality problems across the island. When that eruption ended abruptly in August 2018, emissions from the same area dropped to less than 100 tons per day within two days.
Summit eruptions generally produce less gas than major rift zone events, but the numbers still fluctuate. In the years before 2018, Kilauea’s summit lava lake released around 5,000 tons of sulfur dioxide daily. During the episodic fountaining pattern seen in the current eruption, large amounts of gas (up to 30,000 tons) can be released over a single day of activity, but since episodes happen only once every week or two, the cumulative impact on air quality is less severe than a continuous eruption. Between episodes, emissions drop to a few hundred tons per day.
How Scientists Track What Comes Next
The USGS Hawaiian Volcano Observatory monitors Kilauea around the clock using a network of instruments. Electronic tiltmeters detect tiny changes in the angle of the ground surface, revealing when the magma reservoir beneath the summit is inflating or deflating. GPS stations on opposite sides of the caldera measure the distance between them. When that distance increases rapidly, it signals that the reservoir is swelling with fresh magma.
Seismometers track the small earthquakes that occur as magma forces its way through rock. Gas sensors measure sulfur dioxide output, which rises sharply when magma is close to the surface and actively degassing. Satellite radar (InSAR) provides a broader view of ground deformation across the entire volcano, detecting changes too gradual or widespread for ground-based instruments alone. Together, these tools give scientists a detailed picture of pressure changes underground, often providing hours to days of warning before a new eruptive episode begins.
Kilauea’s position over the Hawaiian hotspot means it will continue receiving magma from the mantle for thousands of years to come. Individual eruptions start and stop as pressure cycles through the shallow plumbing system, but the deeper engine driving it all, a column of hot rock rising from hundreds of kilometers below, shows no sign of shifting away from the Big Island anytime soon.