We use interferometric synthetic aperture radar (InSAR) to study deformation of the summit caldera at Kīlauea Volcano during 2000–2008, which spanned both an east rift zone eruptive event in 2007 and the start of the ongoing summit eruption in 2008. The data set consists of small baseline subset (SBAS) time series generated from 270 acquisitions on three separate beam modes from the Radarsat‐1 satellite. We identify 12 time periods with distinct patterns of displacement that we attribute until late 2003 to secular tectonic‐driven deformation and from 2004 to 2008 to four different sources in the summit area. We model the shallow magmatic system as a spherical reservoir at 1.9 ± 0.1 km depth below the surface to the northeast of Halemaumau (source 1) and three vertically stacked sills at greater depths in the southern caldera area (source 2 at the southern edge of the caldera at 2.9 ± 0.2 km depth, source 3 to the south‐southeast of the caldera at 3.4 ± 0.5 km depth, and source 4 south of the caldera at 3.6 ± 0.4 km depth). The sequence for filling of and withdrawal from these reservoirs reveals a top‐down process, with sequences of both inflation and deflation initiating in the shallowest source. Inflation of source 3 is coincident with elevated seismic activity in the upper east rift zone in February 2006 and May 2007. Source 4 is elongated toward the southwest rift zone and also shows elevated seismicity that extends toward the southwest rift zone.

Volcanoes are hazardous to local and global populations, but only a fraction are continuously monitored by ground-based sensors. For example, in Latin America, more than 60% of Holocene volcanoes are unmonitored, meaning long-term multiparameter data sets of volcanic activity are rare and sparse. We use satellite observations of degassing, thermal anomalies, and surface deformation spanning 17 years at 47 of the most active volcanoes in Latin America and compare these data sets to ground-based observations archived by the Global Volcanism Program. This first comparison of multisatellite time series on a regional scale provides information regarding volcanic behavior during, noneruptive, pre-eruptive, syneruptive, and posteruptive periods. For example, at Copahue volcano, deviations from background activity in all three types of satellite measurements were manifested months to years in advance of renewed eruptive activity in 2012. By quantifying the amount of degassing, thermal output, and deformation measured at each of these volcanoes, we test the classification of these volcanoes as open or closed volcanic systems. We find that~28% of the volcanoes do not fall into either classification, and the rest show elements of both, demonstrating a dynamic range of behavior that can change over time. Finally, we recommend how volcano monitoring could be improved through better coordination of available satellite-based capabilities and new instruments.

Wide-angle refl ections generated by fi ve controlled blasts and over 110 timed quarry blasts in the Southern Appalachians were used to test models for isostatic compensation of topog raphy. The profi les cross the Appa lachian gravity gradient and gravity low and sample the highest elevations within the orogen. Migration of P, SV, and SH refl ections suggests that crustal thickness varies from 35 to 39 km within the coastal plain and 37-39 km within the Carolina terrane. It increases northwestward from 40 to 45 km across the Inner Piedmont, and then thickens to 50-52 km along the southeastern fl ank of the Blue Ridge Mountains. Crustal thickness within the Blue Ridge Mountains ranges from 47 to 56 km. Receiver functions for broadband stations GOGA and MYNC show a similar pattern in crustal thickness. Assuming Airy compensation, the correlation between elevation and Moho depth suggests a range of 50-150 kg/m 3 for the density contrast between the crustal root and mantle. The greatest Moho depths are associated not with the tallest peaks, but rather with the broadest portions of the mountain chain. This observation is consistent with regional bending of the lithosphere. However, the planar basement surface suggests that the root either predates Alleghanian thrusting, and therefore is unrelated to the present topography, or formed in response to some other mechanism. Bounds on curvature of the basement surface suggest a lower bound of 30-40 km for the effective elastic thickness of the lithosphere. This is consistent with previous estimates for the southern Appalachians based on analysis of gravity data.

Analysis of microgravity and surface displacement data collected at the summit of Kīlauea Volcano, Hawaii (USA), between December 2009 and November 2012 suggests a net mass accumulation at 1.5 km depth beneath the northeast margin of Halema'uma'u Crater, within Kīlauea Caldera. Although residual gravity increases and decreases are accompanied by periods of uplift and subsidence of the surface, respectively, the volume change inferred from the modeling of interferometric synthetic aperture radar deformation data can account for only a small portion (as low as 8%) of the mass addition responsible for the gravity increase. We propose that since the opening of a new eruptive vent at the summit of Kīlauea in 2008, magma rising to the surface of the lava lake outgasses, becomes denser, and sinks to deeper levels, replacing less dense gas-rich magma stored in the Halema'uma'u magma reservoir. In fact, a relatively small density increase (<200 kg m À3) of a portion of the reservoir can produce the positive residual gravity change measured during the period with the largest mass increase, between March 2011 and November 2012. Other mechanisms may also play a role in the gravity increase without producing significant uplift of the surface, including compressibility of magma, formation of olivine cumulates, and filling of void space by magma. The rate of gravity increase, higher than during previous decades, varies through time and seems to be directly correlated with the volcanic activity occurring at both the summit and the east rift zone of the volcano.

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