Role of Water Film in Weathering of Porous Rhyolite under Water Unsaturated Condition

Abstract To study weathering behavior under water-unsaturated conditions, flow-through dissolution experiments using a porous rhyolite were performed under both saturated and unsaturated conditions. When water was passed into a dried rock core, water saturation rapidly increased to 0.3 in 2 hours, and then reached 0.4 in 6 days. The proportion of the reactive surface area under the unsaturated condition to that under the saturated condition, A uns/ A s, was 0.46 after 1 day and increased to 0.90 in 6 days. Because A uns/ A s was always greater than water saturation, the surfaces of air- filled pores seemed to be wetted with a water film and dissolved. The water film thickness was estimated to be 2–3 nm. The reason for A uns/ A s