Kīlauea’s explosive magma may have waited years without a final boost

Crystal records from a 900 C.E. eruption point to storage times of less than a year to 12.6 years, with no sign of short-term magma mixing before the blast.

Editorial illustration — not from the study.

A study of crystals from Kīlauea’s largest known summit eruption found that the magma may have remained stored for up to about 13 years. The crystals showed no evidence that a fresh injection of magma mixed in shortly before the eruption.

The findings come from olivine crystals in the Kulanaokuaiki Tephra Unit 3, deposited in an explosive eruption around 900 C.E. The researchers suggest that gas building up as crystals formed in the magma reservoir may have helped drive the eruption, but they present this as a hypothesis.

What the crystals recorded

The researchers studied olivine crystals from the Kulanaokuaiki Tephra Unit 3, the largest known eruption at Kīlauea’s summit. They analyzed 200 crystals: 55% had normal changes in forsterite, a magnesium-rich component of olivine, while 45% showed no such zoning. Among 96 larger zoned crystals, the average composition changed from Fo 89 in the cores to Fo 81 at the rims. Fourteen smaller crystals changed from Fo 85 cores to Fo 82 rims.

Models based on the spread of iron and magnesium in the crystals produced storage times from less than one year to 12.6 years, with a median of three years. Lithium maps from 32 zoned crystals showed several types of lithium patterns. Most were attributed to crystal growth rather than later chemical diffusion, and 17 profiles were linked to phosphorus in the crystals’ outer 100 micrometers, preventing their use for diffusion estimates.

Taken together, the olivine records showed no evidence of magma mixing shortly before the eruption. This differs from earlier findings for Kīlauea’s 1650 C.E. Keanakāko‘i Tephra Unit E eruption. The researchers hypothesize that pressure from gases being squeezed out as small and large crystals formed in the stored magma helped make the Unit 3 eruption explosive.

Why the finding matters

The study challenges the idea that Kīlauea’s explosive eruptions necessarily require a last-minute injection of fresh magma. If the interpretation applies beyond this eruption, explosive magma may remain stored for considerably longer than expected and become hazardous without clear evidence of immediate priming. The result improves understanding of how past explosive activity at Kīlauea may begin, but it does not by itself predict future eruptions.

Evidence and caveats

The study inferred magma storage times from iron-magnesium and lithium patterns in olivine crystals from the 900 C.E. eruption. It assessed 200 crystals, including lithium maps from 32 forsterite-zoned crystals. The modeled timescales range from less than one year to 12.6 years, with a median of three years. These are indirect, model-based estimates from one historic eruption, and the study does not establish how common this storage pattern is at Kīlauea or other volcanoes. The proposed role of gas-driven filter pressing is a hypothesis about how crystallization may have contributed to the eruption’s explosivity.

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