Presenter(s): Eamonn Needham − Earth Sciences
Faculty Mentor(s): Jim Watkins, Thomas Giachetti
Poster 4
Research Area: Earth Sciences (Geology)
Funding: UROP mini grant
The Mono Craters, California eruptions of 1340 C.E. were a series of eruptions that produced relatively texturally homogeneous deposits, with the exception of the first bed. The initial eruptive deposits differ from later deposits in
the relative abundance of obsidian pyroclasts (quenched magma), volatiles (H2O and CO2), and microlites (minerals <100μm). These textural differences between Bed 1 and the other beds remain unexplained, but may be due to changes in decompression rates. To test the decompression rate hypothesis, a sample of synthetic Mono obsidian was run in a cold seal pressure vessel at eruptive conditions. The sample was kept at 850°C and 60 MPa for 2.5 days, and then was decompressed isothermally at a rate of 0.001 MPa/s until it reached 5 MPa. Following rapid quench, bubble number density and microlite number density were determined from scanning electron microscope images. In the future, more of these experiments will be run at different decompression rates, to see which decompression rate best match the textures of the Bed 1 samples. The calculated decompression rate will be compared to decompression rates of later deposits which were calculated in other studies using volatile concentrations. If Bed 1 has a different decompression rate than the later beds, this could explain the textural differences, and can be used to look at how the eruption initiated and progressed. This research could have implications for the ongoing debate of eruptive style transitions from explosive to effusive, which in turn will inform hazard mitigation for volcanoes exhibiting this behavior.