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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Hawaiian lava fountains form when gas-bearing magma rises, pressure falls, and gas bubbles expand fast enough to help propel a mixture of lava and gas into the air. Their height can change as magma supply, gas and bubble behavior, vent geometry, lava properties, and interactions with a lava pool or lake change. A taller fountain does not, by itself, prove that the magma contains more gas.
How a lava fountain forms
Magma beneath a volcano contains gases dissolved in the molten rock. As magma rises toward the surface, pressure decreases. Gas then separates from the melt and forms bubbles; as pressure continues to fall, those bubbles can expand. The expanding gas helps drive a mixture of gas and lava upward through the vent. If that mixture emerges forcefully, it forms a fountain.
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The sequence is easier to picture as rising magma, falling pressure, gas coming out of solution, bubble expansion, and an upward jet. The U.S. Geological Survey (USGS) Hawaiian Volcano Observatory’s March 6, 2025 explainer, “When have lava fountains formed on Kīlauea and what are their hazards?”, compares the gas expansion to what happens when a pressurized drink is opened. That is only an analogy: magma is a hot, complex mixture, and its behavior depends on conditions inside the volcano, not simply on a bottle-like release of pressure.
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Gas is an important part of the process, but a fountain is not just gas escaping from lava. It is a moving mixture whose height reflects how the magma, bubbles, vent, and erupted material interact. The same basic ingredients can produce different-looking fountains under different conditions.
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Why some Hawaiian fountains are episodic and others are sustained
Episodic summit fountains
At Kīlauea’s summit, some eruptions occur in episodes. In the account published by the Hawaiian Volcano Observatory in March 2025, incoming magma is associated with pressure building before an episode. When an episode begins, pressure falls as magma erupts. The repeated buildup and release help explain why summit fountaining can wax and wane rather than remain at one steady height.
Fountains at a moving flank vent
Not every Hawaiian fountain follows that summit pattern. The USGS distinguishes episodic summit activity from the 2018 lower East Rift Zone eruption, where fountains at fissure 8 were driven primarily by a pressure gradient as magma travelled from summit storage toward a lower-elevation vent. The distinction matters: “lava fountain” describes what observers see, but the conditions driving the flow can differ with eruption setting.
These examples are not a complete classification of Hawaiian eruptions. They show why an explanation based on a single pressure cycle should not automatically be applied to every vent or eruption.
What makes a fountain taller or shorter?
Several controls can act together. A change in height may reflect changing supply, gas release, flow through the vent, or the way erupted lava falls back and interacts with the jet. The available studies do not support treating any one of these factors as a universal height dial.
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- Magma supply and volume flux: The amount of magma moving through the vent per unit time affects the flow available to feed the fountain. A change in volume flux can change height even if magma water content is nearly constant, as the 1995 Puʻu ʻŌʻō analysis demonstrated.
- Gas content and bubble behavior: Gas expansion helps propel the mixture. How bubbles form, expand, and merge—or coalesce—can affect how efficiently that gas drives the flow.
- Conduit geometry: The shape and dimensions of the pathway feeding the vent influence how magma and gas move. HVO’s 2026 discussion identifies conduit geometry as one factor likely to affect summit fountain height.
- Viscosity: Lava’s resistance to flow can influence the movement of the erupting mixture. HVO also identifies viscosity as a likely influence, while examining whether chemistry contributes to observed height patterns.
- Re-entrainment and damping: Lava that falls back into a fountain can be drawn into the moving mixture again; this re-entrainment can affect the observed height. A lava pool or lake may also damp the jet. These effects make the visible column more complicated than a direct measure of gas expansion.
Why height is not a gas meter
A particularly useful caution comes from E.A. Parfitt, L. Wilson, and C.A. Neal’s peer-reviewed 1995 study of Puʻu ʻŌʻō fountains during 1983–1986, published in Bulletin of Volcanology 57(6), pages 440–450. The authors concluded that “variations in lava fountain height cannot be simply interpreted as variations in gas content.” Their analysis found that changing volume flux and lava re-entrainment could account for much of the observed height variability even when magma water content was near 0.32 weight percent.
The study also inferred an approximately 0.05 percentage-point decline in gas content across the last ten episodes it analyzed. The authors attributed that inferred decline to more extensive degassing before eruption as the feeder dike became shallower. This is a result from that particular set of Puʻu ʻŌʻō episodes, not a general rate or rule for Hawaiian eruptions.
The distinction is important when interpreting observations. A shorter fountain could be associated with a change in gas content, but it could also reflect changes in flow rate, re-entrainment, or other conditions. Conversely, similar gas content does not guarantee identical fountain heights. The 1995 study suggests that, when height is considered alongside flux and entrainment information, it can help constrain a minimum gas content; height alone cannot identify gas content uniquely.
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In an article dated August 6, 2026, HVO reported fountain heights ranging from 40 to 540 metres across summit eruption episodes 1–51. The observatory described three growth-and-drop periods through episode 43. These values and patterns refer to the episodes covered in that account; they are not a range for every Hawaiian fountain.
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HVO also discussed a relationship between fountain height and magma chemistry. From episode 29 in the third growth period, it reported a consistent positive correlation between MgO and fountain height. In episode 44, both height and MgO declined abruptly, at the same time that a new differentiated olivine population was identified. MgO and fountain heights then rose in episodes 46–48.
These observations make chemistry a clue worth considering, not a settled single-cause explanation. HVO’s account presents conduit geometry, lava viscosity, magma supply rate, and possible chemical effects as factors under consideration. A correlation between MgO and height, or a change coinciding with a new olivine population, does not alone establish that one chemical change caused the fountain pattern.
How scientists measure fountain height
Height estimates depend on defining what counts as the fountain. In its October 28, 2021 explanation, “How high is that lava fountain?”, USGS describes a field method that uses the observer’s distance from the fountain and the angles from eye level to its top and bottom. Trigonometry is used to calculate the upper and lower portions, which are added to obtain the total height.
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The top is the top of the main, continuous lava column—not necessarily the highest glowing particle visible. A gas plume can lift sparse particles tens to hundreds of metres above the continuous fountain. Counting those particles as part of the column would produce a different measurement. USGS’s May 20, 2018 media record also explains the height-measurement question.
Camera measurements at the summit
For the ongoing summit eruption, HVO has also used time-lapse cameras on the south rim. According to the USGS data release dated September 22, 2026, with data updated in August 2026, images were captured at intervals of 0.5–1.0 minute and analysts generally measured fountain height manually about once per minute. They measured the main body and disregarded sparse particles above the continuous fountain.
The release includes measured heights and associated images for episodes 1–50. HVO’s August 2026 article reported 54 episodes by that point, so the data release’s episode coverage and the article’s episode count are not identical. Later episode measurements may not be represented in that release. This is a practical reason to check a dataset’s coverage date and episode range before comparing it with a newer account.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How quickly fountain conditions can change
Historical observations show that a fountain can decline rapidly as vent and lava-lake conditions change. In its account of the 1959 Kīlauea Iki eruption, USGS records a fountain falling from about 210 metres to a few gas bubbles in less than 40 seconds. The lake had risen over the vent, and lava drainback occurred as fountaining ended.
That episode illustrates why a height change should be read in context. The falling fountain did not simply provide a stand-alone measurement of gas content: the relationship between the vent and the rising lake, followed by drainback, was part of the observed change. The historical example does not establish that every rapid decline has the same cause.
Putting a height observation in context
When comparing fountains, start by asking what was measured and where. A main-column height measured from a field observer or camera is not interchangeable with the highest particle carried above it. A summit episode and a flank fissure may have different pressure and flow conditions. A height range reported for a sequence of episodes is not a universal range for Hawaiian eruptions.
Then consider what else was changing: magma supply or volume flux, vent and conduit geometry, lava viscosity, bubble behavior, re-entrainment, and any available chemical observations. The 1995 Puʻu ʻŌʻō study shows why this context matters: changes in flux and re-entrainment explained much of the observed variability in its analysis, while the inferred gas-content decline applied only to the final ten episodes studied. The 2026 HVO discussion, in turn, reports an association between MgO and height over a specified recent episode sequence, while treating chemistry as one possible part of a more complex explanation.
For a historical scale reference, USGS identifies about 680 metres as the maximum historical Hawaiian fountain, during the 1959 Kīlauea Iki eruption. That figure is a reported historical maximum, not a prediction of what a current episode will reach. Read alongside the 40–540-metre range HVO reported for recent summit episodes 1–51, it shows that different eruptions and episode sequences should be kept distinct rather than collapsed into one expected height.
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