Fringes and fractures for episode 30 — USGS Volcano Watch
The past eight months have provided the Island of Hawaiʻi with spectacles of lava fountains at Kīlauea’s summit. These historic episodes began on December 23, 2024, consistently offering locals and visitors a stunning display of lava fountaining nearly weekly. With the 30th episode, came one of the most significant changes since the eruption started—a new fissure in the caldera wall.
COSMO-SkyMed Second Generation (CSG) interferogram for the period from August 2 to August 10, 2025, covering Kīlauea volcano’s summit region. Each color fringe represents 1.55 centimeters (0.61 inches) of ground movement in the direction between the satellite and the ground (range change). The symbol in the upper left indicates the satellite's orbit direction (arrow) and look direction (bar). Earthquakes are marked with circles with the size proportional to their magnitude. The lava flows covering the crater floor are represented by the pink polygon, the two vents (circles) and the new fissure (line) are marked in light pink.
While monitoring data has shown some changes during and between lava episodes, much of this eruption has displayed consistent patterns overall. Two eruptive vents, the north and south, in the southwest part of Halemaʻumaʻu crater have erupted lava fountains feeding lava flows onto the crater floor. These vents have sometimes alternately or simultaneously erupted, with changes in their geometries over time such as growth of the cones around the vents. Nonetheless, the deformation pattern at the summit has been consistent, with inflationary deformation leading up to a fountaining episode, followed by pressure release and deflation during the fountaining itself.
The dominant seismic signal has been tremor, a signal associated with fluid movement (such as magma or gas). Tremor has been weak and occurs along with low-frequency thumping between episodes, then transitions to high-intensity eruptive tremor during the fountaining. Notably, volcano-tectonic earthquakes (brittle fracture) have been infrequent around Kaluapele (Kīlauea’s modern caldera) during this eruption, resulting in overall low earthquake counts.
Episode 30 marked the most significant change in the current eruption. It began, as usual, with lava overflowing from the north vent just before 1 a.m. HST on August 6. However, instead of transitioning to a roaring eruptive tremor and a steady deflationary signal, earthquakes began occurring south of the vents, near the southern caldera walls. These earthquakes were accompanied by a brief 30-minute crack opening signal observed by a tiltmeter station directly to the south, at a location known as Sandhill (SDH).
This pulse of earthquakes was short-lived but clearly indicated shallow rock fracturing, along with nearly two microradians of tilt. These signals preceded the opening of a new fissure to the south against the caldera wall about fifteen minutes later.
Following the opening of the new southern fissure, tiltmeters transitioned to showing deflationary motion typical of fountaining episodes and consistent with the rest of the Kīlauea sensors. The earthquakes then subsided, with only a few events occurring in that region over the next couple of days.
On the south rim of Halemaʻumaʻu, new sink holes in ash that blankets the ground in this area were observed following episode 30 of the Kīlauea summit eruption on August 6. The sinkholes formed due to underlying cracks that opened as a result of the new fissure in the south wall of the caldera. USGS photo by M. Patrick.
A radar interferogram spanning episode 30 shows permanent ground movement near the new eruptive fissure and the area where the earthquakes took place. The ground moved southwest (toward the satellite, during its south-to-north flight) on one side of the fissure, and to the northeast (away from the satellite) on the other. This is shown by repeating color cycles called fringes (see this December 2024 Volcano Watch). The abrupt termination of some of the fringes suggests the ground moved along existing caldera ring faults and ground observations confirmed that new cracks were also created, extending well beyond the new fissure onto the rim of the crater. These observations indicate that the new fissure was fed by a shallow magma (less than half a mile or 1 km deep) that intersected the surface at and near the southern wall of Kaluapele.
Episode 30 behavioral changes serve as an important reminder that while the current eruption has appeared consistent and repetitive, volcanic systems can evolve rapidly, potentially leading to new hazards in areas surrounding the eruption site. At Kīlauea summit, new fissures and cracks may form, and large, fractured cliffs may become unstable and suddenly fall into the caldera. This underscores the hazardous nature of the closed area west of Halemaʻumaʻu, in Hawaiʻi Volcanoes National Park. While residents and visitors enjoy the beautiful spectacle that this eruption has provided, safety should always be a priority and visitors should heed National Park Service guidance.
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Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.
