1,1,4,5,5,6,8,10,11,- 1University of California, Berkeley, Berkeley, CA, USA
- 2Scripps Institution of Oceanography, University of California, San Diego, USA
- 3Earth and Environmental Sciences, Vanderbilt University, Nashville, USA
- 4Institute of Marine Geodynamics, Japan Agency for Marine Earth Science and Technology, Japan
- 5Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole MA, USA
- 6Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Athens, Greece
- 7Université Clermont-Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, Clermont-Ferrand, France
- 8GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
- 9Texas A&M University, College Station
- 10Institute of Geophysics, University of Hamburg, Germany
- 11Graduate School of Science, Kobe University, Japan
- *A full list of authors appears at the end of the abstract
We compare and contrast physical properties (density, P-wave velocity) of volcaniclastic sediments with other uncemented marine sediments. We study cores collected by International Ocean Discovery Program (IODP) Expedition 398, which recovered more than 2200 m of volcaniclastic deposits from 12 sites and 28 holes from Santorini Caldera, Greece, and the surrounding rift basins in the South Aegean Volcanic Arc. The grain density (mass of solids divided by their volume, including any isolated vesicles) of volcaniclastic deposits is typically lower than that of volcanic glass and crystals and is sometimes less than 2 g/cm3, indicating the preservation of isolated gas-filled vesicles in erupted and then deposited materials. To complement bulk measurements, we also measured the total and isolated porosity in individual lapilli-sized volcanic clasts from four different volcanic deposits. We use xray computed tomography to image isolated pore space. Collectively, these measurements confirm that volcaniclastic sediments can preserve vesicle textures and isolated porosity for hundreds of thousands of years and at depths >500 m below sea-level and > 100 m below the seafloor
Volcaniclastic deposits typically have higher P-wave velocities but lower bulk densities than oozes and other marine sediments. In volcaniclastic deposits, lapilli have higher P-wave velocities and lower bulk density than ash, the opposite trend of most sediment in which higher density is correlated with higher seismic velocity. We use granular physics models to show that the higher volcaniclastic P-wave velocity originates from two effects: 1) lower pore volume outside clasts that increases elastic moduli and P-wave velocity and 2) isolated gas vesicles in volcanic clasts that lower bulk density with proportionally less effect on elastic modulii. In volcaniclastic sediments there is relatively little change in physical properties to depths of several hundred meters below the seafloor, which we attribute to rough grain surfaces and lower intergranular (external) porosities that resist compaction and the decrease of intergranular pore space relative to background marine sediment. These trends lead to distinctive signatures of volcaniclastic sediments in reflection seismic images.
Sarah Beethe, Alexis Bernard, Carole Berthod, Hehe Chen, Acacia Clark, Susan DeBari, Tatiana Fernandez Perez, Ralf Gertisser, Raymond Johnston, Christopher Jones, K. Batuk Joshi, Gunther Kletetschka, Olga Koukousioura, Xiaohui Li, Molly McCanta, Anthony Morris, Katharina Pank, Ally Peccia, Paraskevi Polymenakou, Adam Woodhouse
How to cite: Manga, M., Wright, V., Cadena, T., Susman, I., Escogido, C., Ward, S., Kelly, L., Fauria, K., McIntosh, I., Preine, J., Tominaga, M., Nomikou, P., Druitt, T., Kutterolf, S., Ronge, T., Hübscher, C., Karstens, J., and Yamamoto, Y. and the IODP Expedition 398 Scientists: Contrasting seismic velocity and compaction of marine calcareous oozes and volcaniclastic deposits, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4113, https://doi.org/10.5194/egusphere-egu26-4113, 2026.
