Scientists studying Kīlauea’s ongoing summit eruption say changes in magma chemistry may provide clues about why lava fountain heights rise and fall, and whether another period of taller fountains could be developing.
The current summit eruption, which began Dec. 23, 2024, has produced 52 episodes of lava fountains, occurring an average of every 11 days. The fountains have ranged from about 130 feet to 1,770 feet in height.
Since the onset of the eruption, there have been three distinct cycles of fountain height growth followed by a drastic drop in fountain height: episodes 5-16, episodes 17-28 and episodes 29-43. We could be in a fourth growth period that started at episode 44.
While fountain heights are likely controlled by multiple factors such as conduit geometry, lava viscosity and magma supply rate, here we see if magma chemistry could play a role. To determine magma chemistry, we analyze tephra that rapidly cools upon eruption and preserves the pre-eruptive conditions of the magma.
As magma is cooling, moving or interacting with cold solid rock around it, its chemical makeup changes in a process known as magma differentiation. Understanding magma differentiation provides scientists with clues about how magma is behaving beneath the surface. For most of the ongoing eruption, there have not been any significant indicators of magma differentiation.
In Hawaii, one way we track differentiation is by analyzing magnesium oxide (MgO). Higher MgO relates to hotter, fresher magma, and lower MgO is a result of cooler magma. Another way is to analyze the forsterite content in olivine (the green mineral common in Hawaiian lavas), which is a proxy for the composition of the magma from which it crystallized. Olivine forsterite content (Fo) is the ratio between magnesium and iron in the crystal. Higher forsterite contents mean higher magnesium oxide, and thus hotter, fresher magma.
Most of the 52 episodes in the ongoing eruption have produced very similar olivine crystals, which means that enough new magma is being supplied to and erupted from the shallow magma chamber beneath Halemaʻumaʻu that it does not have time to cool or differentiate.
But recently, scientists from the Hawaiian Volcano Observatory recognized a new population of olivine with a slightly different chemistry that erupted in episode 44, and directly after the last abrupt drop in fountain height. These olivine have grown a rim that has a lower magnesium concentration, which means the magma had time to cool and differentiate to a different composition.
One explanation for the origin of the new olivine population could be a decrease in magma supply into the chamber beneath Halemaʻumaʻu. Less fresh, hot magma coming into the system means the existing magma has time to cool and differentiate.
Imagine a malasada as the magma chamber beneath Halemaʻumaʻu and your favorite filling as the magma. Injecting the filling really fast or injecting a high volume of filling is going to over-pressurize your malasada and likely lead to the filling bursting out on the other side (a high fountain episode), and a mess…
Slowly injecting the filling will likely lead to a slower ooze-out (lower fountains), and a cleaner snack. The rate of malasada filling (magma coming into Halemaʻumaʻu chamber) affects the intensity of filling blowout (lava fountain heights).
Tracking the changes in magma chemistry, which is related to the magma supply, could be useful in forecasting periods of fountain growth and decline. The early episodes of the eruption did not show any strong correlations between magma chemistry and fountain heights, but between episode 29 and 48, there has been a consistent correlation: when fountain heights increased, the magnesium oxide also increased. When fountain heights abruptly decreased with episode 44, so did the magnesium oxide and a new population of olivine crystals appeared.
Magnesium oxide and fountain heights have started to increase again in episodes 46 through 48. Given these correlations, it seems there may be a renewed increase in magma supply, and as a result Kīlauea could be entering another fountain growth period.
As the eruption continues, we will continue to test the connection between chemistry and fountain heights, providing potential insights for future episodes. Near-real-time chemical analyses are supported by our cooperative agreement with the University of Hawaiʻi at Hilo and collaboration with other U.S. volcano observatories.