How Hawaiian Lava Fountains Form & Why Heights Change

Updated 5 November 2026 · Standard formula, shown below

This guide explains how Hawaiian lava fountains form and why their heights vary, from a few meters to over 500 meters. You’ll learn the geological processes behind them, the factors that control their intensity, and how to interpret what you see. No special equipment is neededâ€”just an interest in volcanoes.

What You’ll Need

Basic understanding of volcanic processes (magma, gas, eruption)
Access to eruption data (e.g., USGS volcano observatory reports) if you want to compare real examples
A notebook to jot down observations (optional)

Step-by-Step

Understand the source: magma rising from depth. Hawaiian volcanoes are fed by a mantle plume that supplies hot, basaltic magma. As magma rises, pressure decreases, allowing dissolved gases (mainly water vapor, carbon dioxide, and sulfur dioxide) to form bubbles. This is the fundamental driver of fountaining.
Recognize the role of gas exsolution. When magma reaches shallow depths (a few kilometers), the drop in pressure causes gases to exsolve rapidlyâ€”like opening a shaken soda bottle. The bubbles expand and accelerate upward, carrying magma with them. This mixture of gas and molten rock is what erupts as a fountain.
Identify the vent geometry. The shape and size of the volcanic vent control the jet. A narrow, cylindrical vent focuses the gas-magma mixture into a vertical jet, producing a tall fountain. A wide or irregular vent allows gas to escape more diffusely, resulting in lower, less coherent fountains.
Monitor gas content and magma supply. The height of a lava fountain is directly proportional to the gas content of the magma and the rate at which magma is supplied. Higher gas content and faster supply produce taller fountains. Conversely, degassed magma or a reduced supply leads to shorter fountains or effusive lava flows.
Watch for changes in magma viscosity. Hawaiian magmas are basaltic and low in silica, making them relatively fluid. However, even small changes in temperature, crystal content, or bubble nucleation can alter viscosity. More viscous magma traps gas, leading to more explosive fountaining, while less viscous magma allows gas to escape more easily, reducing fountain height.
Observe the eruption style over time. Many Hawaiian eruptions begin with a vigorous fountaining phase, which may last hours to days. As the eruption continues, gas content and magma supply often decrease, causing fountain heights to decline. The system may also pulse, with fountains rising and falling in cycles.
Consider external factors. Tidal stresses, earthquakes, or changes in the magma plumbing system can temporarily affect gas release and fountain height. These are secondary but can cause noticeable variations.

Common Mistakes

Assuming fountain height equals eruption intensity. A tall fountain does not always mean a large volume of lava; it can be due to high gas content with relatively low magma output.
Ignoring the effect of wind. Strong trade winds can bend a lava fountain, making it appear shorter than it is. Always measure vertical height, not the length of the tilted jet.
Confusing lava fountains with lava lakes. A lava lake is a persistent pool of molten lava in a crater, while a fountain is a transient jet. They can coexist, but they are different phenomena.
Overlooking the role of degassing before eruption. If magma sits in a shallow chamber and degasses slowly, the eruption may be less fountaining and more effusive. The gas content at the moment of eruption is what matters.

Tips

To estimate fountain height, use a known reference (e.g., a crater rim or a tall tree) and compare. For precise measurements, use a theodolite or photogrammetry.
Check real-time data from volcano observatories (like USGS) to see how fountain heights correlate with seismic tremor and gas emissions.
Remember that fountains can be intermittent; a single observation may not represent the average behavior. Watch for several minutes to get a sense of the pattern.
If you are near an eruption, always follow safety guidelinesâ€”stay far away, wear a respirator for volcanic gases, and heed evacuation orders.

Troubleshooting

If you expected a tall fountain but see only lava flows: The magma may have already degassed before reaching the surface. Check if the eruption is occurring from a vent that has been open for a while, allowing gas to escape continuously.
If fountain heights are erratic: This could indicate a changing gas supply or a partially blocked vent. Listen for rhythmic tremor patterns, which often correspond to pulsing fountains.
If the fountain suddenly stops: This may be due to a drop in magma supply or a vent collapse. Watch for subsequent changes in the vent shape or the onset of explosive activity.
If you are comparing fountain heights from different eruptions: Be sure to account for differences in vent size, magma composition, and measurement methods. Direct comparisons can be misleading.

Frequently Asked Questions

What is the tallest recorded Hawaiian lava fountain?

The tallest recorded fountain in HawaiÊ»i reached about 580 meters during the 1959 KÄ«lauea Iki eruption. Most fountains are much shorter, typically under 100 meters.

Why do some eruptions produce fountains while others just flow?

The key is gas content. If magma contains abundant dissolved gases that exsolve rapidly at the vent, it will fountain. If the magma has already degassed (e.g., by sitting in a shallow chamber), it will flow out as a lava flow.

Can lava fountains occur under water?

Yes, submarine eruptions can produce fountains, but the water pressure suppresses gas expansion, so they are usually less vigorous than subaerial fountains. The water also rapidly quenches the lava into pillow lavas.

How long do lava fountains typically last?

Individual fountains can last from minutes to hours. A fountaining episode may continue for days or weeks, but often with fluctuating intensity. For example, the 1969â€“1974 Mauna Ulu eruption had many episodes of fountaining, each lasting hours to days.

Is lava fountain height related to earthquake activity?

Yes, there is often a correlation. The rise of magma and gas causes seismic tremor. High tremor usually corresponds to more vigorous fountaining, while a lull in tremor may precede a decrease in fountain height.

Can lava fountains be predicted?

Scientists can forecast the likelihood and general intensity of fountaining based on monitoring gas emissions, ground deformation, and seismicity. However, exact heights and timing are not predictable with precision.

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.