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We conducted gravity surveys of the summit area of Kilauea Volcano, HawaiModified Letter Turned Commai, in November 2018 and March 2019, with the goal of determining whether there was any mass change at depth following the volcano's May-August 2018 caldera collapse. Surface deformation between the two surveys was minimal, but we measured a gravity increase (maximum 44 mu Gal) centered on the caldera that can be modeled as mass accumulation in a region similar to 1 km beneath the surface. We interpret this mass increase to be mostly magma accumulation in void space that was created during the summit collapse. Caldera uplift was evident by April 2019, indicating that the magma volume had reached a point where pressurization could be sustained. Modeled gravity change suggests a maximum magma storage rate at Kilauea's summit during November 2018 to March 2019 that is much less than the pre-2018 magma supply rate to the volcano.

Plain Language Summary Measuring changes in gravity over time at a volcano provides an indication of mass variation beneath the surface, which can offer evidence of whether or not magma is accumulating in, or draining from, subsurface reservoirs. After the 2018 collapse of Kilauea Volcano, Hawai.i, there was uncertainty over the status of subsurface magmatic activity. We found that an increase in gravity occurred between November 2018 and March 2019. The gravity increase was not accompanied by uplift of the surface, which implies that mass, probably magma, was accumulating in void space created during the collapse. The rate of magma accumulation was much less than the pre-2018-collapse magma supply rate. By April 2019 Kilauea was inflating, indicating that the magma reservoir beneath the summit had filled to the point that pressure could be sustained.