Volcano Watch: Peering into a crystal ball — What tiny crystals can tell us about their trip through the magma chamber

“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-doctoral researcher Heather Winslow.

Like fortune tellers who peer into a crystal ball for insight, volcanologists at Hawaiian Volcano Observatory peer into the tiny crystals contained in lava flows to learn about magma’s journey before it erupted onto the surface.

When magma cools prior to eruption, crystals grow and develop chemical zones that record changes in the environment around them. Scientists study chemical differences in these zones, which can provide information about:

• How hot the magma was (thermometry).
• How deep it was stored (barometry).
• What the compositional makeup of the magma was (geochemistry).
• How long the magma was stored prior to an eruption (diffusion chronometry).

What is fascinating is that these micron-scale changes — measured to 0.00004 of an inch — in individual crystals can be used to derive understanding about volcanic systems as a whole.

To give some context, a human hair is about 100 microns (0.004 of an inch) thick. We are looking at chemical changes in crystals on the scale of 1 to 5 microns (0.00004 to 0.0002 of an inch), and those very small changes tell us what was happening to the magma prior to it erupting at the surface.

The most common mineral we study in Hawaiʻi is the green-colored olivine. We can use olivine as a “crystal clock” to determine the timing of magmatic events leading up to eruption, which was discussed in detail in a previous “Volcano Watch.”

Two other minerals we observe in Hawaiian eruptions are pyroxene and plagioclase.

While olivine is typically the first mineral to crystallize, pyroxene and plagioclase crystallize later and thrive in different magmatic environments at different temperatures and pressures.

An easy way to think about these crystals and how they record magmatic events is to envision yourself as a journalist outside a sporting event.

You need to know what happened at the game (the magmatic event) by interviewing different spectators (crystals). Some spectators show up early and witness the entire event. Some arrive late. Others are seated close to the action, and some roamed the stadium and forgot certain events even happened.

The analogy originated from observing the complexities and nuances in olivine alone, but it can be extended to apply to the variety of crystals in the magmatic system as well.

Different crystals are all observing the the magmatic event from different perspectives, thus we get to learn about the magmatic system from those same perspectives.

This method was applied to study the two most recent eruptions of Kīlauea in collaboration with the University of Hawaiʻi at Hilo Geology Department.

Kīlauea erupted Sept. 15-20 in and near Nāpau Crater on the middle East Rift Zone. During the opening phase of this eruption, we collected molten magama and spatter samples that were rapidly cooled by submerging them in water or quenched in the air, preserving the pre-eruptive chemistry.

We analyzed bulk chemistry from those samples, which showed compositional differences compared to typical lavas erupted at Kīlauea summit. While there was evidence for new magma intrusion into Nāpau Crater area through seismic and deformation data, the chemistry indicated previously stored magma was erupted from the rift zone.

Plagioclase crystals from the opening phases of the eruption had unique chemical zoning; the interior reflects growth in magma that was likely previously stored, while the outer zone has a different chemistry that was influenced by the new magma that intruded from the summit.

Kīlauea summit started erupting in Halemaʻumaʻu Crater on Dec. 23, 2024, and is now in its fourth eruptive episode.

Hawaiian Volcano Observatory staff collected molten samples of lava from the caldera floor and airfall samples from the lava fountain that fell on the crater rim.

Olivine crystals analyzed from the first episode of the eruption mostly show typical Kīlauea summit compositions; however, some minerals show differences between their cores and rims that could suggest magmatic transfer from multiple magma storage regions beneath the summit.

These differences in crystal compositions helps us understand what happened to the magmas beneath the surface.

If you’re interested in learning more about Hawaiʻi’s active volcanoes, see the Volcano Awareness Month schedule of events here.

Volcano Activity Updates

Kīlauea is erupting. Its U.S. Geological Survey Volcano Alert level is at Watch.

The eruption within Halemaʻumaʻu at the summit of Kīlauea resumed just after 9 a.m. Jan. 15, after being paused for nearly 12 days.

A small sluggish lava flow began at about 9:15 a.m. exiting the north vent and lava fountaining resumed at same vent by 10 a.m.

The south vent became active at about 11:40 a.m. Jan. 15, also with lava fountaining and associated lava flows.

Hawaiian Volcano Observatory reported Jan. 16 in its daily Kīlauea update that field crews observed lava fountain heights of 295 to 330 feet from the north vent and 130 to 160 feet from the south vent.

Both fountains were active overnight, with the north vent fountain consistently higher than the south.

Field crews reported lava fountain heights of 160 feet and 140 feet from north and south vents, respectively, the morning of Jan. 16.

Crews also reported that at about 8:25 a.m. Jan. 16 parts of the south vent collapsed, with an associated reduction of about half in south vent lava fountain height.

Lava flow activity has remained confined to the southwest crater floor area near the active vents.

Lava continued to fountain as of about 7:15 p.m. Jan. 16 as seen from the livestream of the summit.

The onset of episode 4 began toward the end of the time window, from Jan. 9-15, that Hawaiian Volcano Observatory identified when an eruption restart was most likely. The summit has steadily deflated as the newest episode continues.

No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

Sulfur dioxide emission rates are elevated in the summit region.

Earthquake rates in the Southwest Rift Zone and upper-to-middle East Rift Zone remained comparable to the previous week. Ground deformation rates outside of the summit region remained steady.

There were reports the morning of Jan. 16 of Pele’s hair falling on nearby communities, specifically the Volcano Golf Course subdivision.

Kīlauea updates are issued daily while eruptive activity continues, and contain the most recent eruption information.

Mauna Loa is not erupting. Its Volcano Alert Level is at Normal.

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

• Magnitude-2.9 at 10:44 a.m. Jan. 13 located 7 miles south-southeast of Fern Forest at a depth of 4 miles.
• Magnitude-3.1 at 11:27 a.m. Jan. 12 located 6 miles northeast of Pāhala at a depth of 20 miles.
• Magnitude-3.2 at 10:34 a.m. Jan. 10 located 11 miles north-northeast of Honoka‘a at a depth of 7 miles.
• Magnitude-3.1 at 9:31 a.m. Jan. 10 located 11 miles northeast of Kukuihaele at a depth of 3 miles.
• Magnitude-3.1 at 8:30 a.m. Jan. 9 located 8 miles south of Fern Forest at a depth of 4 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.