Assoc. Professor Stephen Obrochta (Akita Univ. Japan)

Title: “Mt. Fuji Holocene eruption history reconstructed from proximal lake sediments and high-density radiocarbon dating using a new age-depth model”

Time & Location: 11:00 am, 26th Feb & Madsen Building F09, USYD.

Abstract: An 8000-year lacustrine sediment record from Lake Motosu (Fuji Five Lakes) records several eruptions, including potentially unreported events, of the active Mt. Fuji volcano, which receives approximately 47 million annual visitors. A high-fidelity age model is constructed from tephra ages and high-density radiocarbon dating of terrestrial macrofossil and bulk organic matter using a new, deterministic age model. Variability in lake reservoir age is constrained by modern lake water radiocarbon measurement and reverse calibration of tephra calendar ages. We present more accurate ages for known eruptions, detect a wider distribution of ejecta for several eruptions, including the most recent summit eruption, and potentially identify previously undetected flank eruptions. There are closely spaced scoria-fall layers that may be difficult to differentiate as separate events in land-based surveys. These results demonstrate the utility of lacustrine sediments as powerful tools for understanding characteristics of volcanic eruptions.

Bio: Undergrad at Eckerd College, Florida looking at hardbottom formation, erosion, origin in mixed carbonate-siliciclastic systems. Masters at University of South Florida, continuing looking at mixed carbonate-siliciclastic systems but in Australia with ODP 194 sediments attempting to indirectly constrain GBR timing. PhD at Duke University working on climate variability and ice sheet dynamics with IODP Exp. 303 material. Looking at the nature of millennial climate variability prior to the last glacial cycle and re-evaluating supposed periodicities in millennial climate change