Accurate forecasts of lava flow length rely on estimates of eruption and magma properties and, potentially more challengingly, on an understanding of the relative influence of characteristics such as the apparent viscosity, the yield strength of the flow core, or the strength of the lava's surface crust. For basaltic lavas, the relatively high frequency of eruptions has resulted in numerous opportunities to test emplacement models on such low silica lava flows. However, the flow of high silica lava is much less well understood due to the paucity of contemporary events and, if observations of flow length change are used to constrain straightforward models of lava advance, remaining uncertainties can limit the insight gained. Here, for the first time, we incorporate morphological observations from during and after flow field evolution to improve model constraints and reduce uncertainties. After demonstrating the approach on a basaltic lava flow (Mt. Etna 2001), we apply it to the 2011-2012 Cordón Caulle rhyolite lava flow, where unprecedented observations and syn-emplacement satellite imagery of an advancing silica-rich lava flow have indicated an important influence from the lava flow's crust on flow emplacement. Our results show that an initial phase of viscosity-controlled advance at Cordón Caulle was followed by later crustal control, accompanied by formation of flow surface folds and large-scale crustal fractures. Where the lava was unconstrained by topography, the cooled crust ultimately halted advance of the main flow and led to the formation of breakouts from the flow front and margins, influencing the footprint of the lava, its advance rate, and the duration of flow advance. Highly similar behavior occurred in the 2001 Etna basaltic lava flow. In our comparison of these two cases, we find close similarities between the processes controlling the advance of a crystal-poor rhyolite and a basaltic lava flow, suggesting common controlling mechanisms that transcend the profound rheological and compositional differences of the lavas.

Understanding lava flow processes is important for interpreting existing lavas and for hazard assessments. Although substantial progress has been made for basaltic lavas our understanding of silicic lava flows has seen limited recent advance. In particular, the formation of lava flow breakouts, which represent a characteristic process in coolinglimited basaltic lavas, but has not been described in established models of rhyolite emplacement. Using data from the 2011-2012 rhyolite eruption of Puyehue-Cordón Caulle, Chile, we develop the first conceptual framework to classify breakout types in silicic lavas, and to describe the processes involved in their progressive growth, inflation, and morphological change. By integrating multiscale satellite, field, and textural data from Cordón Caulle, we interpret breakout formation to be driven by a combination of pressure increase (from local vesiculation in the lava flow core, as well as from continued supply via extended thermally preferential pathways) and a weakening of the surface crust through lateral spreading and fracturing. Small breakouts, potentially resulting more from local vesiculation than from continued magma supply, show a domed morphology, developing into petaloid as inflation increasingly fractures the surface crust. Continued growth and fracturing results in a rubbly morphology, with the most inflated breakouts developing into a cleft-split morphology, reminiscent of tumulus inflation structures seen in basalts. These distinct morphological classes result from the evolving relative contributions of continued breakout advance and inflation. The extended nature of some breakouts highlights the role of lava supply under a stationary crust, a process ubiquitous in inflating basalt lava flows that reflects the presence of thermally preferential pathways. Textural analyses of the Cordón Caulle breakouts also emphasize the importance of late-stage volatile exsolution and vesiculation within the lava flow. Although breakouts occur across the compositional spectrum of lava flows, the greater magma viscosity is likely to make late-stage vesiculation much more important for breakout development in silicic lavas than in basalts. Such late-stage vesiculation has direct implications for hazards previously recognized from silicic lava flows, enhancing the likelihood of flow front collapse, and explosive decompression of the lava core.

Slope instability at mine sites is a hazard that may persist long after closure. Stewards of such assets can monitor and assess the associated risks by examining ground displacement over time. Mapping ground displacement through satellite Interferometric Synthetic Aperture Radar (InSAR) is an increasingly common tool for mine site monitoring. The satellite returns image acquisitions at regular time intervals, which are compared to each other to measure displacement.InSAR is a remote sensing technique that can provide wide-area, high-precision data coverage, regardless of cloud cover. However, for InSAR to provide coverage, the radar reflectivity of the ground needs to stay consistent throughout the analysis period. This consistency is hindered by changes on the ground surface, such as construction, excavation, snow or water inundation, and the type, thickness, and seasonal variation of vegetation. These can be challenging variables across active sites, due to ongoing mining activities, and at closed sites, due to deconstruction of infrastructure, revegetation and any other process that alters the ground surface. These challenges are present at one such site, which has been anonymised in this article, where closure activities make conventional InSAR workflows challenging. At this site, to be able to provide critical ground displacement data, more than 100 artificial radar corner reflectors (CRs) were deployed. These are metal structures carefully located and positioned to provide a strong, consistent radar response across desired assets.The use of CRs for InSAR is not new, but they have not been widely adopted for mining applications, especially in large numbers. Our results demonstrate the benefits of using CRs for such applications, including improved precision and enhanced data coverage over key assets, such as the tailings storage facility. The success of the project highlights the importance of a collaborative approach in planning an InSAR monitoring program. Further, this study discusses challenges of InSAR and CR use for closed mine sites and provides alternative InSAR technologies to CRs that could be used for the application of mine closure.

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