## 6 Conclusions  
InSAR has revealed several deformation events at Pacaya Volcano, Guatema, after eruptions on the 27 and 28 of May 2010. Three meters of co-eruptive displacement of the southwest flank is followed by several months of material consolidation, giving a rare glimpse of flank stabilization processes. The rapid initiation and cessation of flank displacement is unique from other measurements of volcanic flank movement, which have typically been attributed to gravitational creep. Localized deformation near the summit likely reflects the subsidence of historic lava flows deposited to the north of the cone, although the complicated signal makes it difficult to discern specific flows. Alternatively, this feature may indicate slow crystallization and cooling of newly intruded magma, which implies a complex conduit system. Interferograms also reveal the emplacement and subsequent subsidence of a 5.4-km long lava flow, which is the first historic flow to erupt outside of the ancestral collapse scarp. We attribute its eruption location to both the local transstensional stress regime and the structurally weak zone as a result of southwest flank displacement. The recurrence of these high-volume lava flows erupting from flank vents additionally suggests a cyclical pattern of high-level magma systems draining into lower vents. The existence of shallow magma within the cone has serious implications for the already unstable volcano. This is particularly true given the repeated pattern of magma intrusion along a NNW-orientation, perpendicular to the flank displacement. The utility of InSAR for measuring the complex geophysical signals at Pacaya is evident given the variety of deformation measurements revealing both eruptive and non-eruptive behavior. In particular, the high spatial resolution of aerial  
Figure 7: Eruptive trends at Pacaya. (**a**) A continued NNW-oriented pattern of vents and cracks is seen post-2010 eruption. Intrusions along this weakness zone could have provided the push to induce slope displacement during the May 2010 eruption. Cracks were mapped using Google Earth aerial images (inset image taken in December 2010, courtesy of Google 2015 DigitalGlobe); (**b**) High volume lava flows tend to erupt from lower flank vents such as in 1961, 1975, 2010, and 2014, suggesting a cyclical draining of a shallow magma system in the cone. Outlines for the 1961 and 1975 lava flows from [21]. UAVSAR has proven to be an excellent compliment to satellite data, particularly when it comes to constraining motion components. Although direct measurement comparisons between the two sensors is limited due to the lack of temporal overlap, future ALOS-2 missions could benefit from UAVSAR acquisitions. The deformation detected at Pacaya promotes the future use of InSAR at this and other potentially unstable volcanoes. [PERSON] acknowledges support provided by the NASA Earth and Space Science Fellowship Program (NNX13 AO50H) and the AEG (Association of Environmental and Engineering Geologists) Foundation. [PERSON] acknowledges support from the NASA Earth Surface and Interior Program (NNX14 AQ95G) and the Shuler-Foscue Endowment at Southern Methodist University (Dallas, TX, USA). ALOS-1 (Advanced Land Observing Satellite) data were acquired from the Japan Aerospace Exploration Agency via the Alaska Satellite Facility through the WInSAR (Western North America Interferometric Synthetic Aperture Radar) Consortium, and were processed using Gamma software ([[http://www.gamma-rs.ch/](http://www.gamma-rs.ch/)]([http://www.gamma-rs.ch/](http://www.gamma-rs.ch/))). UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar) interferograms were courtesy of the NASA Jet Propulsion Laboratory-California Institute of Technology. The authors wish to thank three anonymous reviewers for helping to improve this manuscript. [PERSON], [PERSON], and [PERSON] conceptualized the manuscript and provided revision throughout the study. [PERSON] drafted the manuscript. [PERSON] and [PERSON] processed InSAR data.