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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteKīlauea’s summit fountains come in episodes because the volcano releases pressure in bursts. According to U.S. Geological Survey (USGS) tilt observations, the summit swells as pressure builds, fountaining begins as that pressure is released through the north and south vents, and the summit sinks once the release is underway. Each cycle then starts again. That repeating sequence is the most useful answer to why the eruption switches on and off, and it explains much of what a viewer sees: a fountain, a pause, and then another fountain.
How the pressure cycle works
The USGS describes the summit eruption as a cycle with three stages. Watching the summit’s tilt, which is a sensitive measure of how the ground is bending, makes each stage visible.
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Inflation: pressure builds before an episode
Between episodes the summit rises as magma and gas accumulate in the chambers beneath it. The ground’s gradual swelling is the signal that pressure is rising toward the level needed to force material out of the vents.
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When the episode begins, the north and south vents release the pressure that has accumulated in the summit magma chambers. Fountaining is the visible result. Because each release relieves only part of the accumulated pressure, the system can settle and build again.
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Deflation: the summit sinks as pressure drops
Once the episode is under way, the summit switches from inflating to deflating. The tilt record therefore shows a rise, a sharp reversal, and a fall for each cycle. That pattern is the strongest observational basis for the on-and-off behavior.
What the cycle does not fully explain
The pressure cycle accounts for the timing of episodes, but it does not settle every detail of how each fountain behaves. Explanations that attribute the whole process to one gas-bubble mechanism go beyond what the monitoring record shows. Treat any single-mechanism account of an individual fountain’s height or duration as an open question.
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From one fountain to a longer eruption
The current summit eruption is a series of episodes, not one continuous fountain. The USGS episode timeline records the following events. Its most recent entries run through September 16, 2026, so later activity may have occurred after that date.
| Date | Event | Recorded by |
|---|---|---|
| December 23, 2024 | The current summit eruption begins. | USGS episode timeline |
| August 25, 2026 | Episode 54, the most recent fountain episode in the timeline. It lasted nine hours and reached 150 feet. | USGS episode table |
| September 14–16, 2026 | Six new vents open in and near the northwest wall of Halemaʻumaʻu and produce lava flows without fountaining. | USGS timeline |
The September 14–16 event is a separate lava-flow episode, not a fountain episode. Counting it as a fountain would overstate the number of fountains in the record.
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Why fountain heights vary so much
The headline height is a maximum, and maxima are easy to misread. The table below separates the highest reported figure from a single documented episode.
| Measure | Value | How to read it |
|---|---|---|
| Highest fountain height reported | 1,570 feet (479 meters) above the vents | An observed maximum reported by the USGS in 2026. It is not a typical height. |
| Episode 54 (August 25, 2026) | 150 feet; nine hours | One documented episode, shown in the USGS episode table. |
The USGS episode table records height, duration, the vents that were active, and the interval since the previous episode. Comparing episodes on those four measures gives a more accurate picture than the single highest figure. An episode’s height and duration can differ widely from the next one, so a spectacular episode should not be taken as the norm.
What the fountain throws into the air
The USGS uses the term tephra for the material a fountain launches. In its words:
“Tephra is a word for any volcanic material that is erupted and travels through the air before landing on the ground.” — U.S. Geological Survey, Kīlauea eruption information, 2026
Tephra covers several kinds of material:
- Ash: the finest fragments.
- Reticulite: light, frothy volcanic glass. Gas-rich lava can cool quickly into this texture.
- Scoria: denser, vesicular volcanic rock fragments.
- Volcanic bombs: larger fragments that are thrown out and land near the vents.
- Pele’s hair: fine strands of volcanic glass.
Fountain height and wind decide where the material lands. Most of it has fallen southwest of the vents, within a closed area of Hawaiʻi Volcanoes National Park, but the USGS documents occasional impacts farther away. Pele’s hair and other glassy fragments can irritate skin and eyes, and they can contaminate catchment water. Visitors should handle any glassy fragments with care and avoid collecting them near active areas.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.The gases that come with the fountains
Fountains release volcanic gases, mainly water vapor, carbon dioxide, and sulfur dioxide. The USGS reports sulfur dioxide emission rates that differ sharply between episodes and pauses:
| Condition | Sulfur dioxide emission rate | Qualification |
|---|---|---|
| During fountaining episodes | Up to 75,000 tonnes per day | USGS, 2026. The USGS cautions that some episode rates may be higher than the measurements it captured. |
| When fountains are inactive | About 1,200–1,500 tonnes per day | USGS, 2026. |
The gas figures show that the pauses between episodes are not periods of silence. Sulfur dioxide continues to leave the summit between fountains, although at a much lower rate.
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Checking current status before you rely on this
Activity at Kīlauea can change within days, so verify the current situation before planning around it:
- Open the USGS Kīlauea eruption updates and read the most recent entry in the episode table.
- Compare that entry’s date with September 16, 2026. If the latest entry is later, the episode count, heights, and gas figures in this article are out of date.
- Check Hawaiʻi Volcanoes National Park for current closures and designated viewing locations. The active crater floor is closed to the public.
What Kīlauea does and does not show about other volcanoes
The pressure cycle described here comes from observations of Kīlauea’s summit during the current eruption. It is a clear example of episodic release at one volcano. The evidence in this article does not establish how other volcanoes fountain, so the title’s broader comparison should be read as an analogy rather than a general rule.
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