Volcano Watch: Where does Kīlauea tephra go? The answer is blowin’ in the wind
“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.
The spectacular series of Kīlauea eruptive episodes during the past 6 months has been remarkably safe for public viewing, but a simple change in wind or brief vent collapse could cause dramatic shift in the hazards produced by the volcano.
Recent “Volcano Watch” articles described the episodic nature of this eruption, with episodes of lava fountains separated by pauses. Other “Volcano Watch” articles described hazards associated with the lava fountaining.
The extent and severity of hazards associated with lava fountaining depend on three factors:
- Lava fountain height.
- Wind conditions.
- 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. Incredibly, these spectacular fountains are still shorter than the record 1,900-foot fountains of the 1959 Kīlauea Iki eruption.
Taller fountains mean more tephra — pieces of the lava fountain, which includes Pele’s hair — can be deposited further away, as the starting point from which tephra begins to fall to the ground is higher up.
The ongoing eruption has created a hill of tephra southwest of Halemaʻumaʻu Crater, 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 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 because of volcanic gas and vog — or volcanic smog — plus small amounts of Pele’s hair might 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 Volcano Golf Course to ʻŌhiʻa 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.
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 during strong persistent trade winds with speeds of 9 to 14 mph. Episode 24 fountains reached 1,200 feet during trades with speeds of 5 to 10 mph.
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.
The tephra deposit was visible for both in satellite imagery up to 2.5 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 toward the sky, water falls 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 at Kīlauea Iki and 1969 at Maunaulu after the cone partially collapsed into the vent during lava fountaining, causing 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 more than a mile away from the vents, they are not likely to be directly affected in the unlikely event of an inclined fountain.
Hawaiian Volcano Observatory continues to monitor Kīlauea’s summit eruption and its hazards, working closely with Hawaiʻi Volcanoes National Park and Hawaiʻi County Civil Defense.
The combination of an episodic lava fountain and hurricane season is rare, and its good to maintain an awareness of which way the wind is blowing.
Volcano Activity Updates
Kīlauea has been erupting episodically within the summit caldera since Dec. 23, 2024. Its U.S. Geological Survey Volcano Alert Level remains at Watch.
Episode 26 of the Kīlauea summit eruption in Halemaʻumaʻu Crater occurred June 20, with about 9 hours of sustained lava fountaining from the north and south vents. Summit region inflation since the end of Episode 26, along with persistent tremor, suggests another eruptive episode is possible and could start between June 29 and July 3.
Sulfur dioxide emission rates are elevated in the summit region during active eruption episodes. No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.
Mauna Loa is not erupting. Its U.S. Geological Survey Volcano Alert Level remains at Normal.
No earthquakes were reported felt in the Hawaiian Islands during the past week.
Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa.
Visit the observatory’s website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.
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