Volcano Watch: Handling the pressure; what gases trapped inside crystals tell us

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week’s article was written by Hawaiian Volcano Observatory post-doc researcher Heather Winslow.

Volcanic gases can give us critical information in the lead up to a hazardous eruption.

Hawaiian Volcano Observatory scientists use permanent and portable gas monitoring stations to measure gas concentrations and emission rates above the surface of our volcanoes.

But to look at gases below the surface, we turn to petrologists — a scientist who studies the origins of rocks and minerals — who can find gases trapped within volcanic rocks.

Gases within volcanic rocks can be measured to estimate gas compositions and magma storage depths before lava erupts on the surface.

In geology, we call gases below the surface volatiles, referring to the elemental composition of the gas, which can be a solid, liquid or vapor phase.

When referred to as a gas, it means a volatile transitioned into the vapor phase. The most common gases — or vapor phase volatiles — emitted at the surface are water, carbon dioxide and sulfur dioxide.

But how can we measure volatiles trapped within the magma before it erupts?

By analyzing tiny droplets that become trapped within crystals such as olivine. These tiny droplets, called inclusions, can contain different materials.

Melt inclusions contain the magma, in solid form, while fluid inclusions can contain drops of water, carbon dioxide and sulfur dioxide in the liquid or gas phase.

Once an inclusion is trapped, the surrounding crystal acts as a pressure-capsule and retains information about the magma at the time the inclusion was formed.

Fluid inclusions in volcanoes are dominantly composed of carbon dioxide. At magmatic temperatures — 2,192 degrees — the density of the carbon dioxide strongly depends on pressure, which is influenced by the depth of the magma at that point in time.

Thus, if we can measure the density of the carbon dioxide within a fluid inclusion, we can estimate the pressure at which that fluid inclusion was trapped in the growing crystal and infer the depth under the volcano where the magma was when that crystal grew.

Determining storage depths of crystals has large implications for how we understand volcanoes and how shallow or deep magmas reside below the surface before they rise to erupt.

Fluid inclusion density is measured by creating thin slices of the crystals that are analyzed using Raman Spectroscopy.

One challenge in this process, however, is that fluid inclusions are so very tiny they can be hard to identify!

They can range in size from about 0.0004 to 0.004 inches in diameter.

Hawaiian Volcano Observatory scientists in 2025 conducted and participated in a short workshop at University of Hawaiʻi at Hilo for undergraduate students and professors discussing fluid inclusion sample preparation and identification.

University of Hawaiʻi at Hilo students and staff learned laboratory techniques for identifying fluid inclusions and how to properly prepare the crystals for Raman Spectroscopy.

This process is a recently developed method, and results for magma storage depths can be attained very quickly after sample collection.

An undergraduate student in the University of Hawaiʻi at Hilo Geology Department helped initiate the fluid inclusion workshop because of their research interests in using this technique to estimate the depth magma was stored before recent Kīlauea eruptions.

The collaborative relationship between Hawaiian Volcano Observatory and University of Hawaiʻi at Hilo Geology Department has been strengthened through the years because of a cooperative agreement established in 1998.

University of Hawaiʻi at Hilo undergraduate students participate in eruption response and apply what they learn in the classroom directly to impactful work with Hawaiian Volcano Observatory.

During each new eruption at Kīlauea, this technique provides another important tool for Hawaiian Volcano Observatory scientists to understand hazards in Hawaiʻi’s frequent eruptions.

Preliminary results from episodes that span from mid-January 2025 to early July 2025 show that the magmas came from about 1 mile deep beneath the surface, which is the location of the shallow Halemaʻumaʻu magma chamber.

VOLCANO ACTIVITY UPDATES

KĪLAUEA

VOLCANO ALERT LEVEL: Watch

Kīlauea has been erupting episodically since Dec. 23, 2024, within its summit caldera. Episode 41 lava fountaining happened for just more than 8 hours on Jan. 24. No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

WHAT’S NEXT? Summit region inflation since the end of Episode 41 indicates another lava fountaining episode is possible and could occur between Feb. 13 and 17, with it mostly likely between Feb. 14 and 16.

MAUNA LOA

VOLCANO ALERT LEVEL: Normal.

Mauna Loa is not erupting. Read more about the volcano online in the monthly update by Hawaiian Volcano Observatory.

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

EARTHQUAKES

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

• MAGNITUDE-3.1 at 5:59 p.m. Feb. 7 located 6 miles east of Pāhala at a depth of 18 miles.
• MAGNITUDE-3.1 at 3:36 a.m. Feb. 7 located 4 miles north of Hala‘ula at a depth of 24 miles.

Visit the Hawaiian Volcano Observatory 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.