Volcanoes Erupt Stressed Quartz Crystals

• Published in: Geophysical research letters Vol. 46; no. 15; pp. 8791 - 8800
• Main Authors: Befus, K. S., Manga, M., Stan, C., Tamura, N.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.08.2019; American Geophysical Union; Wiley
• Subjects: Ascent; Bearing; Brittleness; Calderas; Cargo; Cargo handling; Crystal lattices; Crystals; Deformation; Deformation analysis; Density currents; diffraction; force chain; fragmentation; GEOSCIENCES; Hazards; In situ measurement; Lava; Magma; Magma chambers; Quartz; Quartz crystals; Residual stress; Storage conditions; supereruption; synchrotron; Volcanic activity; Volcanic eruptions; Volcanoes; Yellowstone; Long Valley
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL083619

Volcanic eruptions are energetic events driven by the imbalance of magmatic forces. The magnitudes of these forces remain poorly constrained because they operate in regions that are inaccessible, either underground or dangerous to approach. New techniques are needed to quantify the processes that drive eruptions and to probe magma storage conditions. Here we present X‐ray microdiffraction measurements of volcanic stress imparted as lattice distortions to the crystal cargo of magma from Yellowstone and Long Valley eruptions. Elevated residual stresses between 100 and 300 MPa are preserved in erupted quartz. Multiple volcanic forces could be culpable for the deformation so we analyzed crystals from pyroclastic falls, pyroclastic density currents, and effusive lavas. Stresses are preserved in all quartz but cannot be attributed to differences in eruption style. Instead, lattice deformation likely preserves an in situ measurement of the deviatoric stresses required for the brittle failure of viscous, crystal‐bearing glass during ascent. Plain Language Summary Because of inherent danger, volcano scientists have little direct understanding of the stresses active during volcanic eruptions. We propose that the crystal cargo carried by a volcanic eruption may preserve a record of those stresses. We used synchrotron X‐ray microdiffraction to measure crystal deformation in quartz from explosive and effusive eruptions from Yellowstone and Long Valley calderas. All the crystals were strained by stresses ranging from 100 to 300 MPa. These values are large but are not related to eruption style. The stresses may have been caused by crystal‐crystal impingements in the crystal‐rich magma chambers. More likely, we propose that the residual stresses record those required for brittle failure of the crystal‐bearing melt in the conduit during eruptive ascent. Key Points Explosive and effusive eruptions from volcanoes contain deformed quartz crystals with the same residual stresses Residual stresses are proposed to originate from the stresses required to fragment magma Residual stress may also originate from crystal‐crystal contacts in crystal‐rich magmatic mushes