Japan Geoscience Union Meeting 2018

Presentation information

[EE] Evening Poster

S (Solid Earth Sciences) » S-VC Volcanology

[S-VC39] Pre-eruptive magmatic processes: petrologic analyses, experimental simulations and dynamics modeling

Thu. May 24, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Michihiko Nakamura(Division of Earth and Planetary Materials Science, Department of Earth Science, Graduate School of Science, Tohoku University), Akihiko Tomiya(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Shanaka L de Silva (共同), Fidel Costa(Earth Observatory of Singapore, Nanynag Technological University)

[SVC39-P15] Permeability measurements of heated and unheated ash erupted from Aso Volcano

*Atsuko Namiki1, Yukie Tanaka1, Tadashi Yokoyama1 (1.Graduate School of Integrated Arts and Sciences, Hiroshima University)

Keywords:Ash, reheating

The eruption of the Aso Volcano during 2014-2016 is mainly classified into ash eruption but Strombolian eruption, erupting scoriae rather than ash, is also observed (e.g., Yokoo and Miyabuchi, 2015). Such a transition may depend on the generation of ash and physical properties of the ash layer at shallow conduit. Ash once erupted out from the vent sometimes falls back. The reheated ash may stick together, that increases its strength and decreases its permeability. In order to characterize this process we heated the ash sampled from Aso Volcano sieved with a 53μm mesh at high temperature (950℃, 700℃, and 500℃) under normal stress of 26kPa. Only when the temperature is high enough (950℃), the ash stick together to be an ash plate. Next, we measured the permeability of this ash plate and unheated ash by using gas flow. The permeability of the ash plate is less than 2x10-13 m2, while that for ash is larger than 10-11m2; i.e., heating decreases the permeability of ash more than 2 orders of magnitude. Interestingly, the unheated ash particles can freely move in the container during the permeability measurements. This effect allows making pipe-like structures in the ash layer and increases its permeability with flow rate. Our measurements suggest that the sticking of ash can occur at 950℃ even under low normal stress, as low as 1m thickness of an ash layer. Once the sticking of ash particles occurs, that inhibits the movement of ash particles and restrict the gas flow in the ash layer.