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Deformation of the ground surface at active volcanoes provides information about magma movements at depth. Improved seafloor deformation measurements between 2011 and 2015 documented a fourfold increase in magma supply and confirmed that Axial Seamount's eruptive behavior is inflation-predictable, probably triggered by a critical level of magmatic pressure. A 2015 eruption was successfully forecast on the basis of this deformation pattern and marked the first time that deflation and tilt were captured in real time by a new seafloor cabled observatory, revealing the timing, location, and volume of eruption-related magma movements. Improved modeling of the deformation suggests a steeply dipping prolate-spheroid pressure source beneath the eastern caldera that is consistent with the location of the zone of highest melt within the subcaldera magma reservoir determined from multichannel seismic results.

Axial Seamount is the best monitored submarine volcano in the world, providing an exceptional window into the dynamic interactions between magma storage, transport, and eruption processes in a mid‐ocean ridge setting. An eruption in April 2015 produced the largest volume of erupted lava since monitoring and mapping began in the mid‐1980s after the shortest repose time, due to a recent increase in magma supply. The higher rate of magma replenishment since 2011 resulted in the eruption of the most mafic lava in the last 500–600 years. Eruptive fissures at the volcano summit produced pyroclastic ash that was deposited over an area of at least 8 km2. A systematic spatial distribution of compositions is consistent with a single dike tapping different parts of a thermally and chemically zoned magma reservoir that can be directly related to previous multichannel seismic‐imaging results.

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[1] The Ganges, Brahmaputra, and Meghna rivers converge in Bangladesh with an annual discharge second to the Amazon. Most of the flow occurs during the summer monsoon causing widespread flooding. The impounded water represents a large surface load whose effects can be observed in Gravity Recovery and Climate Experiment (GRACE) and GPS data. Bangladesh is at the center of the second largest seasonal anomaly in the GRACE gravity field, reflecting water storage in Southeast Asia. Eighteen continuous GPS stations in Bangladesh record seasonal vertical motions up to 6 cm that inversely correlate to river level. We use 304 river gages to compute water height surfaces with a digital elevation model to separate surface water from groundwater. Porosity of 20% was used to estimate groundwater mass and calculate the water load. Results show ∼100 GT of water are stored in Bangladesh (7.5% of annual discharge) but can reach 150 GT during extreme events. The calculated water mass agrees with monthly GRACE water mass equivalents from Bangladesh within statistical limits. We compute the deformation due to this water load on an elastic half-space, and we vary Young's modulus to fit GPS data from our two most continuous records. The water loading can account for >50% of the variance in the GPS data. The best fitting Young's modulus is 117-124 GPa for DHAK and 133-135 GPa for SUST, although the upper bound is not well constrained. These estimates lie between sediment (30-75 GPa) and mantle (190 GPa) values, indicating that response to loading is sensitive to structure throughout the lithosphere and is not absorbed by the weak sediments.