Volcano Watch: What tiny crystals can tell us about their trip through the magma chamber

Volcano Watch is a weekly article and activity update written by US Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week’s article was written by HVO post-doctoral researcher Heather Winslow. 

Like fortune tellers who peer into a crystal ball for insight, volcanologists at the USGS Hawaiian Volcano Observatory peer into the tiny crystals contained in lava flows to learn about the magma’s journey before it was 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 on how hot the magma was (thermometry), how deep it was stored (barometry), what the compositional makeup of the magma was (geochemistry), and how long the magma was stored prior to an eruption (diffusion chronometry).

What is fascinating is that these micron-scale (0.00004 inches) changes 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 inches) thick. We are looking at chemical changes in crystals on the scale of 1-5 microns (0.00004–0.0002 inches), and those very small changes tell us what was happening to the magma prior to it erupting at the surface.

In Hawaii, the most common mineral we study 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 here. 

Two other minerals that 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 of a sporting event, and you need to know what happened at the game by interviewing different spectators (crystals). Some spectators show up early and witness the entire event, some arrive late, some are seated close to the action, and some roamed the stadium and forgot certain events even happened. Different crystals are the different fans that are all observing the game (or magmatic event) with a different perspective. 

This analogy originated out of observing the complexities and nuances in olivine alone, but it can be extended to apply to the variety of crystals in magmatic system as well. Thus, by studying the range of crystals, we get to learn about the magmatic system from a multitude of 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. From September 15-20, 2024, Kīlauea erupted in and near Nāpau Crater on the middle East Rift Zone. During the opening phase of this eruption, we collected molten and spatter samples that were rapidly cooled by submerging the samples in water or quenched in the air. This preserves the pre-eruptive chemistry. 

From those samples, we analyzed bulk chemistry, 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 that previously stored magma had been 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 erupted at Halemaʻumaʻu from December 23, 2024, to January 3, 2025, in three distinct episodes. HVO 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 of Kīlauea. 

These differences in crystal compositions helps us understand what happened to the magmas beneath the surface.  If you’re interested in learning more about Hawaii’s active volcanoes, see the Volcano Awareness Month schedule of events here.

Volcano Activity Updates

Kīlauea is erupting. Its USGS Volcano Alert level is WATCH.

The eruption within Halemaʻumaʻu at the summit of Kīlauea resumed just after 9 a.m. on Wednesday, Jan. 15, after being paused for nearly 12 days. Small fountains began at about 5:40 a.m. followed by lava flows just after 9 a.m. and the resumption of fountaining from the northern vent by 10 a.m. The onset of episode 4 began toward the end of the time window (January 9-15) that HVO had identified where an eruption restart was most likely. Kīlauea summit has been steadily deflating as episode 4 of the eruption 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. 

Maunaloa is not erupting. Its USGS Volcano Alert Level is at NORMAL.

Five earthquakes were reported felt in the Hawaiian Islands during the past week: a M2.9 earthquake 12 km (7 mi) SSE of Fern Forest at 7 km (4 mi) depth on January 13 at 10:44 a.m. HST, a M3.1 earthquake 10 km (6 mi) NE of Pāhala at 33 km (20 mi) depth on January 12 at 11:27 a.m. HST, a M3.2 earthquake 19 km (11 mi) NNE of Honoka‘a at 11 km (7 mi) depth on January 10 at 10:34 a.m. HST, a M3.1 earthquake 19 km (11 mi) NE of Kukuihaele at 5 km (3 mi) depth on January 10 at 9:31 a.m. HST, and a M3.1 earthquake 14 km (8 mi) S of Fern Forest at 7 km (4 mi) depth on January 9 at 8:30 a.m. HST.

HVO continues to closely monitor Kīlauea and Maunaloa.

Visit HVO’s website for past Volcano Watch articles, Kīlauea and Maunaloa updates, volcano photos, maps, recent earthquake information, and more. Email questions to askHVO@usgs.gov.