Where does Kīlauea tephra go? The answer is blowin' in the wind — USGS Volcano Watch

The spectacular series of Kīlauea eruption episodes over the past six months has been remarkably safe for public viewing, but a simple change in the wind or brief vent collapse could cause dramatic changes in the hazards the volcano presents.

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This animated GIF shows a timelapse sequence consisting of one image every several days between December 25, 2024, and June 20, 2025. The photos were taken from the northern rim of the caldera, near Uēkahuna overlook and the view is south towards the ongoing eruption site in Halemaʻumaʻu. The sequence shows the dramatic development of a tephra cone on the rim of Halema‘uma‘u during the twenty-six episodes of lava fountaining that have occurred between December 23, 2024, and June 20, 2025. USGS images.

Recent Volcano Watches have described the episodic nature of this eruption, with episodes of lava fountains separated by pauses. Other Volcano Watches have described hazards associated with lava fountaining.

The extent and severity of hazards associated with lava fountaining depend on three factors: (1) lava fountain height, (2) wind conditions, and (3) lava fountain angle.

Overall, lava fountains during this eruption have been getting higher. This pattern is not guaranteed to continue, but the four most recent episodes have erupted the highest lava fountains—all taller than 1,000 feet (300 meters). Incredibly, these spectacular fountains are still shorter than the record 1,900-foot (580 meter) fountains of the 1959 Kīlauea Iki eruption.

Taller fountains means that more tephra (pieces of the lava fountain, which includes Pele’s hair) can be deposited further away, as the starting point from which tephra starts to fall to the ground is higher up. The ongoing eruption has created a hill of tephra southwest of Halemaʻumaʻu—similar to how tephra fallout from the 1959 Kīlauea Iki fountains formed Puʻupuaʻi. During the last four episodes the hill has grown by as much as 30 feet (10 meters) in a single episode! The growing hill hasn’t posed a hazard to the public as it is within a closed area of Hawaiʻi Volcanoes National Park—but this brings us to wind.

Dominant trade wind conditions generally send tephra and volcanic gas southwest over the remote Kaʻū Desert. Eruption viewing areas within the national park are unaffected, but there can be decreased air quality in communities downwind of Kīlauea due to volcanic gas, vog (“volcanic smog”), and small amounts of Pele’s hair may fall.

Future episodes could occur during less favorable conditions, or during wind patterns affected by hurricanes. This already happened: episodes 15 and 16 occurred during low and variable winds, and Pele’s hair fell on nearby communities—from the Volcano Golf Course to Ohia Estates and beyond. During episode 15, tephra also fell at Uēkahuna and Kīlauea overlooks, resulting in the temporary closure of these popular viewing areas, while during episode 16, tephra fell on Highway 11.

Sources/Usage: Public Domain.

These maps show lava flow and tephra accumulation at Kīlauea volcano associated with episodes 23 (left) and 24 (right) of the ongoing eruption in Halemaʻumaʻu that started on December 23, 2024, using data recorded by the Italian Space Agency's (ASI) COSMO-SkyMed Second Generation satellite constellation. These maps combine cross-polarized radar amplitude images taken on two different dates, along with interferometric coherence from the time between those dates. In the maps, unchanged barren areas are represented in blue/purple, vegetated areas appear in yellow/light green, and new deposits over barren land are shown in either dark or bright green. Large yellow dots show measured tephra deposit thickness, and the dotted circle encompasses distances within 1.3 miles (2.1 kilometers) of the eruptive vents. Public viewing areas within Hawaiʻi Volcanoes National Park are indicated with white squares; these can be temporarily closed for public safety.

What if an episode occurs during Kona winds (the opposite direction from trade winds)? Recent episodes provide a guide. Episode 23 fountains reached 1,150 feet (350 meters) during strong persistent trade winds with speeds of 9–14 miles/hour, and episode 24 fountains reached 1,200 feet (365 meters) during trade winds with speeds of 5–10 miles/hour. Both times, tephra deposits were up to 2 feet thick a mile directly downwind—about the same distance as from the vents to Kīlauea overlook. For both, the tephra deposit was visible in satellite imagery up to 2½ miles away—slightly less than the distance from the vents to Volcano House. This corresponds to an inch or less of tephra.

What about lava fountain angle? Imagine a garden hose blasting water. If the nozzle is pointed straight towards the sky, water will fall back down on the ground nearby—although wind can send the water downwind. This is the default behavior of lava fountains. An “inclined fountain” happens when the nozzle is angled away from the sky (a change in vent geometry) or if there is a partial blockage.

Inclined fountains happened briefly and suddenly in 1959 (Kīlauea Iki) and 1969 (Maunaulu) after the cone partially collapsed into the vent during lava fountaining (a partial blockage). It took up to 20 minutes for the blockages to clear and the fountain to straighten itself. As the nearest viewing areas of the current eruption are over a mile away from the vents, they are not likely to be directly affected in the unlikely event of an inclined fountain.

The USGS Hawaiian Volcano Observatory (HVO) will continue to monitor Kīlauea's summit eruption and its hazards, working closely with Hawaiʻi Volcanoes National Park and the Hawaiʻi County Civil Defense Agency. The combination of an episodic lava fountain and hurricane season is rare and it's good to maintain an awareness of which way the wind is blowing.

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.