Volcano Watch: All in a day’s work; determining magma storage depths at Kīlauea

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. Today’s article is by postdoctoral scholar Charlotte L. Devitre and assistant professor Penny E. Wieser with University of California, Berkeley.

Consider a can of soda.

When the can is closed, or pressurized, the soda contains dissolved carbon dioxide. When you open the can, the pressure drops, bubbles form and rise.

Molten rock, or magm, beneath the Earth’s surface behaves similarly, and we can learn from the gas trapped in tiny bubbles preserved in crystals from the rock after it’s erupted on the surface as lava.

As magma rises from 67 miles deep beneath the surface, the pressure drops and bubbles form. When trapped within growing crystals, these bubbles — smaller than the width of a human hair — are called fluid inclusions.

At volcanoes such as Kīlauea, the bubbles are primarily carbon dioxide, the density of which in a fluid inclusion is sensitive to the pressure the magma was under when the gas was trapped in a crystal.

The greater the depth — and pressure — the magma was below the surface, the higher the carbon dioxide density, providing a precise record of magma storage depths.

By measuring carbon dioxide densities in lots of fluid inclusions, scientists can determine the depth at which the gas became trapped in crystals, and hence the depth of magma storage before eruption.

In September 2023, Kīlauea erupted within Kaluapele, the summit caldera, and a team of scientists from University of California, Berkeley partnered with scientists from Hawaiian Volcano Observatory to carry out a rapid response exercise.

They wanted to determine whether fluid inclusions could be analyzed in near real time to provide information about magma storage depths during an eruption.

Typically, this type of information is not easy to obtain quickly. If the team could demonstrate a fast and successful technique obtaining it, that technique could complement monitoring efforts at many volcanoes.

Hawaiian Volcano Observatory scientists collected tephra samples and mailed them to University of California, Berkeley. Upon receipt, University of California, Berkeley scientists began their laboratory work around 9 a.m. Pacific Standard Time.

They crushed the samples, picked out and polished olivine crystals to find the fluid inclusions and measured their carbon dioxide densities using a Raman spectrometer.

By the end of the day, about 7 p.m. Pacific Standard Time, data from 16 crystals was collected and analyzed. The data, which was shared with Hawaiian Volcano Observatory, showed that the erupted magmas were stored in Kīlauea’s shallowest magmatic reservoir at a depth of 0.6 to 1.2 miles prior to eruption.

This depth is relatively typical of small summit eruptions; whereas, larger eruptions such as the 2018 lower East Rift Zone eruption often sample magmas coming from depths of 2 to 3 miles.

In the 2 days that followed, University of California, Berkeley scientists continued to collect data to determine whether the results were biased by the small number of analyses.

However, the outcome remained the same, indicating the results obtained the first day provided a good insight into the storage depth of magma supplying the September 2023 summit eruption of Kīlauea.

This method works well in Hawaiʻi because the magma in our volcanoes contains very little dissolved water, a key to the success of the fluid inclusion work. Many other volcanoes around the world have magmas with far more water, at which the fluid inclusion work would not work.

To determine whether this technique could be applied to other volcanoes besides Kīlauea, University of California, Berkeley scientists compiled a large database of analyses of melt inclusions from other frequently erupting volcanic systems in the world including Iceland, Galápagos Islands, East African Rift, Réunion, Canary Islands, Azores and Cabo Verde.

Volcanoes in these places are sufficiently “dry” for the fluid inclusion method to be successful.

Ultimately, the study demonstrated this technique can successfully be applied to provide information about the source depth of the magma erupting at the surface in near real time during eruptive events at many different volcanoes globally.

Understanding the depth that bubbles were trapped in the crystals, along with other monitoring datasets, can co-inform estimates of the size of an eruption and be used to draw analogues with past eruptions.

For instance, in future events at Kīlauea, identifying the contribution of deeper-stored magmas in near real time — retrospectively found for the 2018 lower East Rift Zone eruption of Kīlauea — could potentially be helpful to inform the possibility of the eruption developing into a larger event.

Volcano Activity Updates

Kīlauea has been erupting episodically within its summit caldera since Dec. 23, 2024. Its U.S. Geological Survey Volcano Alert Level is at Watch.

The eruption continued during the past week, with one eruptive episode. Episode 13 was active from the morning of March 11 until later that same afternoon. Kīlauea summit has been inflating since Episode 13 ended, suggesting another eruptive episode is possible.

Sulfur dioxide emission rates are elevated in the summit region during active eruption episodes. No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

Mauna Loa is not erupting. Its U.S. Geological Survey Volcano Alert Level is at Normal.

Four earthquakes were reported felt in the Hawaiian Islands during the past week:

• Magnitude-3.7 at 11:33 p.m. March 11 at 19 miles southeast of Pāhala and depth of 20 miles.
• Magnitude-3.4 at 12:46 a.m. March 11 at 10 miles southeast of Pāhala and depth of 20 miles.
• Magnitude-3.4 at 4:08 p.m. March 10 at 3 miles west of Puakō and depth of 21 miles.
• Magnitude-3 at 10:33 p.m. March 8 at 8 miles east of Pāhala and depth of 17 miles.

Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa.

Visit the volcano observatory’s website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.