Volcano Watch: Tracking magma movement using olivine crystal ‘clocks’

Images of olivine from Hawaiian volcanoes. In olivine the abundance of magnesium (Mg) is expressed as the forsterite content (Fo) — which is a ratio of how much Mg there is compared to the iron (Fe). Left: Green olivine from Mauna Loa’s 1852 eruption, viewed under a microscope. Middle: Zoomed in electron image of the inside of an olivine from Kilauea’s December 2020 eruption, where grayscale indicates the relative abundance of iron (Fe). The darker core (black inside) of the olivine is higher in Mg (and a higher Fo content) than the lighter rim (gray outside). This crystal is approximately 800 microns (0.3 inches) across. Right: Another electron image of olivine from 29 September 2021 that also has changes in Fo content between the core and rim. This crystal is smaller, only 400 microns (0.15 inches) across. (Photos courtesy, left to right, USGS photo by K. Lynn and University of Hawaii at Manoa electron microprobe/Special to West Hawaii Today)

Lavas and their minerals erupted from Hawaiian volcanoes provide clues to the history of the magmas that are eventually erupted. Kilauea’s recent summit eruptions allow us “a glimpse inside” the volcano and the chance to learn more about where the magma erupted in Halema‘uma‘u crater came from and how quickly it moved to the surface.