A brief but spectacular eruption at the summit of Kīlauea early on October 1, 2025, sent fountains of lava soaring to extraordinary heights, with the tallest jets reaching an estimated 1,300 feet. The intense event, which lasted just over six hours, originated from two distinct vents within Halemaʻumaʻu crater, adding another dramatic chapter to the volcano’s ongoing eruptive sequence that began in late 2024. All activity was contained within Hawaiʻi Volcanoes National Park and posed no immediate threat to nearby communities.
The powerful outburst, designated Episode 34 of the current summit eruption, began shortly before 1 a.m. Hawaii Standard Time and ended abruptly just after 7 a.m. Scientists at the Hawaiian Volcano Observatory (HVO) reported that the event expelled approximately 8.9 million cubic yards of molten rock onto the crater floor. The eruption was characterized by the simultaneous activity of two vents behaving in different ways, providing a remarkable display of volcanic dynamics and showcasing the complex plumbing system beneath one of the world’s most active volcanoes.
An Eruption of Two Vents
The eruptive episode unfolded in stages, starting with precursory activity the night before. Low lava fountains, about 30 feet high, began bubbling from a north vent at 11:43 p.m. on September 30. This activity intensified until 12:53 a.m. on October 1, marking the official start of Episode 34. Throughout the eruption, the north vent produced fountains that reached heights of up to 330 feet, which were notably inclined toward the northeast.
A second, more powerful vent to the south joined the eruption at approximately 1:45 a.m. This southern vent quickly became the dominant feature of the episode. Unlike the angled spray from its northern counterpart, the south vent ejected lava in a nearly perfect vertical column. It was this vent that produced the towering 1,300-foot fountains, a height that rivals many skyscrapers. This powerful fountaining continued for most of the eruption’s six-hour duration before activity at both vents ceased within minutes of each other. The south vent stopped at 7:00 a.m., followed by the north vent at 7:03 a.m.
Geophysical Signals of the Outburst
Volcanologists closely tracked the underground changes that precipitated and accompanied the eruption. The onset of the high fountains was linked to a distinct shift in ground deformation at Kīlauea’s summit. Before the event, instruments recorded a steady inflation of the summit magma chamber, with tiltmeters registering about 18 microradians of upward tilt since the previous episode. This indicated that magma was accumulating and pressurizing the system.
At 12:53 a.m., precisely as the main fountaining phase began, the summit rapidly began to deflate. This sudden reversal signaled that magma was no longer pushing the ground up but was instead rushing to the surface. During the six-hour eruption, the Uēkahuna tiltmeter recorded approximately 26 microradians of deflationary tilt, a direct measurement of the volume of magma that had just been discharged. The end of the episode was marked by an equally swift halt to the deflation and a decrease in seismic tremors, with the summit beginning to inflate once more as the magma chamber started to repressurize.
Volume and Flow Characteristics
In its short duration, Episode 34 was remarkably voluminous, erupting about 2.5 billion gallons of lava. The erupted material contributed to the ever-changing landscape on the floor of Halemaʻumaʻu crater, which has been steadily filling since the current eruptive period began in December 2024. The lava flows from this episode were contained entirely within the southern part of the caldera, a deep, bowl-shaped depression at the volcano’s summit.
Even after the fountaining stopped, HVO scientists noted that the newly emplaced lava flows would continue to exhibit slow movement and incandescence for several days as they cooled and solidified. The eruption did not affect Kīlauea’s East Rift Zone or Southwest Rift Zone, indicating the event was confined to the summit’s magmatic system. Due to the northeasterly trade winds, the National Weather Service issued a statement warning of possible ashfall in the Kaʻū district, southwest of the volcano. Other airborne hazards included elevated levels of sulfur dioxide gas and Pele’s hair, which are thin, sharp fibers of volcanic glass that can be carried downwind.
Monitoring and Public Safety
The U.S. Geological Survey’s Hawaiian Volcano Observatory continuously monitors Kīlauea with a dense network of scientific instruments. Despite a concurrent federal government shutdown that limited some public communications, the agency maintained its core monitoring duties and issued necessary alerts. Essential updates, including volcanic activity notices for aviation, were distributed even as the agency’s social media channels remained silent.
The volcano’s alert level remained at WATCH, with an aviation color code of ORANGE, reflecting the ongoing potential for eruptive activity without threatening populated areas. All eruptive activity occurred within a section of Hawaiʻi Volcanoes National Park that has been closed to the public since 2007 due to persistent hazards such as unstable cliff walls and toxic volcanic gases. Park officials continued to manage safe viewing areas for the public, who gathered to witness the dramatic, though distant, lava display.
Historical Volcanic Context
Kīlauea is one of the most active volcanoes on Earth, with a history of both effusive lava flows and more explosive, powerful eruptions. The towering fountains of Episode 34 are among the most vigorous observed in the current eruption sequence. They draw comparisons to past events, notably the 1959 eruption in the nearby Kīlauea Iki crater, which produced lava fountains reaching heights of 1,050 feet.
The current activity at the summit is part of a longer eruptive phase that began on December 23, 2024, characterized by these episodic bursts of high fountaining. This pattern of cyclic inflation and deflation, followed by rapid lava release, is a hallmark of the volcano’s modern behavior, which scientists can now track with high precision using sensitive tiltmeters and GPS stations. This episode is another reminder of the dynamic and powerful forces at work beneath the surface of Hawaiʻi’s Big Island.
