Under Construction: Rebuilding Kīlauea's Shallow Magma Storage System After Caldera Collapse

Draining of Kīlauea's upper level magma reservoir system in ~1500 CE led to a N-S elongate, roughly circular structural caldera ~6.5 km in diameter surrounding a prominent topographic caldera (TC) 4 x 3 km in diameter. The TC was probably at least 600 m deep with a volume of ~4-6 km3. The reservoir system has been rebuilding since then, mostly during the past 200 y of relatively high magma supply. Current reservoir locations are well defined geodetically (Poland et al., 2014) but do not match the presumed configuration of magma storage before the caldera collapse, if the common assumption holds that collapse width equals reservoir width. For example, magma does not underlie the northern 1-2 km of the TC, as judged by relatively high P-wave velocities (Dawson et al., 1999) and lack of deformation related to magma storage. The northernmost reservoir, near Halemaumau, is within the TC, but an order of magnitude more magma fills the south caldera reservoir south of the TC (Poland et al., 2014). Currently, the Halemaumau reservoir is shallower than the south caldera reservoir (1-2 km vs. 3-4 km), but in the 1960s magma was likely stored 3-3.5 km deep near Halemaumau (Wright and Klein, 2014). Many deformation centers are south of the TC and have an E-W spread of ~4 km. These observations suggest an evolving storage system that, if drained today, would not form a caldera of the size or location of the TC. Yet the TC is at the summit of the volcano, the site of an older caldera (Holcomb, 1987) and a positive Bouguer gravity anomaly (Kauahikaua et al., 2000), and is apparently the preferred location of reservoir draining and caldera collapse. We think the reservoir system will continue to evolve, expanding and centering itself below the topographic caldera, which will likely be where the next collapse takes place. Dawson et al., 1999, GRL. Holcomb, 1987, USGS PP 1350. Kauahikaua et al., 2000, Geology. Poland et al., 2014, USGS PP 1801. Wright and Klein, 2014, USGS PP 1806.