Fig. 3: Two-step dehydration.
From: Magma chamber decompression during explosive caldera-forming eruption of Aira caldera
a Distributions of water content along a 300-μm-long melt embayment calculated by the one-dimensional diffusion model. The decompression rate is assumed as 1 × 103 Pa s−1. The initial water content is 6.5 wt%. The distributions of water 12, 24, 36, and 48 h after the start of decompression are shown. The measured data of water contents shown in each panel are the same as those in Fig. 2a. The gray hatched area (~50 μm from the entrance of the embayment) is considered to be affected by the rapid dehydration in the second decompression step and/or post-eruption hydration. b Diffusion profiles formed in the embayment when the magma is decompressed to atmospheric pressure at different decompression rates, calculated by the one-dimensional diffusion model (red solid line). The numbers shown in the profiles indicate the decompression rate (×103 Pa s−1). The initial water content of sample 171129 C is 6.5 wt%, samples 181218B2 and 181218B3 are 6.0 wt%, 181218B4 is 5.0 wt%, and 140901F8 is 4.0%, decreasing with the progress of the eruption.
