Consider a can of soda. When the can is closed (pressurized), the soda contains dissolved carbon dioxide (CO2). When you open the can, the pressure drops, bubbles form and rise. Molten rock (magma) 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 magma rises from 100 km (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 like Kilauea, the bubbles are primarily CO2. The density of CO2 in a fluid inclusion is sensitive to the pressure the magma was under when the CO2 was trapped in a crystal. The greater the depth (and pressure) the magma was below the surface, the higher the CO2 density, providing a precise record of magma storage depths.
By measuring CO2 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 Sept. 2023, Kilauea erupted within Kaluapele (the summit caldera), and a team of scientists from University of California Berkeley (UCB) teamed up with scientists from the USGS Hawaiian Volcano Observatory (HVO) to carry out a rapid response exercise.
They wanted to determine whether fluid inclusions could be analyzed in near-real-time to provide information on magma storage depths during an eruption. Typically, this type of information is not easy to obtain quickly. If the team of scientists could demonstrate a fast and successful technique for getting this information, it could complement monitoring efforts at many volcanoes.
HVO scientists collected tephra samples and mailed them to UCB. Upon sample receipt, the UCB scientists began their laboratory work around 9 a.m. Pacific Standard Time (PST). They crushed the samples, picked out and polished olivine crystals to find the fluid inclusions, and measured their CO2 densities using a Raman spectrometer.
By the end of the day, around 7 p.m. PST, data from 16 crystals had been collected and analyzed. The data, which was shared with HVO, showed that the erupted magmas had been stored in Kilauea’s shallowest magmatic reservoir at 1-2 km (0.6-1.2 miles) depth prior to eruption. This depth is relatively typical of small summit eruptions whereas larger eruptions, like the 2018 lower East Rift Zone eruption, often sample magmas coming from 3-5 km (2-3 miles) depth.
In the following two days, UCB scientists continued to collect data to determine whether the results had been biased by the small number of analyses. However, the outcome remained the same, indicating that the results obtained the first day provided a good insight into the storage depth of magma supplying the September 2023 summit eruption of Kilauea.
This method works well in Hawaii 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 Kilauea, UCB scientists compiled a large database of analyses of melt inclusions from other frequently erupting volcanic systems in the world, including Iceland, the Island of Hawai‘i, 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 that this technique can successfully be applied to provide information on 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 Kilauea, identifying the contribution of deeper-stored magmas in near-real-time—retrospectively found for the 2018 lower East Rift Zone eruption of Kilauea—could potentially be helpful to inform the possibility of the eruption developing into a larger event.
Volcano activity updates
Kilauea has been erupting episodically within the summit caldera since December 23, 2024. Its USGS Volcano Alert level is WATCH.
The summit eruption at Kilauea volcano that began in Halem‘uma‘u crater on December 23 continued over the past week, with one eruptive episode. Episode 13 was active from the morning of March 11 until later that same afternoon. Kilauea summit has been inflating since episode 13 ended, suggesting that 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 Kilauea’s East Rift Zone or Southwest Rift Zone.
Mauna Loa is not erupting. Its USGS Volcano Alert Level is at NORMAL.
Four earthquakes were reported felt in the Hawaiian Islands during the past week: a M3.7 earthquake 19 km (11 mi) SE of Pahala at 33 km (20 mi) depth on March 11 at 11:33 p.m., a M3.4 earthquake 17 km (10 mi) SE of Pahala at 33 km (20 mi) depth on March 11 at 12:46 a.m., a M3.4 earthquake 6 km (3 mi) W of Puako at 34 km (21 mi) depth on March 10 at 4:08 p.m., and a M3.0 earthquake 13 km (8 mi) E of Pahala at 27 km (17 mi) depth on March 8 at 10:33 p.m.
Please visit HVO’s website for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake information, and more. Email questions to askHVO@usgs.gov.
Charlotte L. Devitre is a postdoctoral scholar and Penny E. Wieser is an assistant professor at the University of California at Berkeley.
