Abstract
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 cooling limited basaltic lavas, but has not been described in established models of rhyolite emplacement. Using data from the 2011–2012 rhyolite eruption of Puyehue-Cordon 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 Cordon 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 Cordon 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.
Highlights
Studies of hazards from silicic volcanic eruptions usually focus on explosive activity partly because effusive silicic eruptions are rare events
Our multiscale data analysis of breakouts and the main lava flow brings together satellite imagery, digital elevation models (DEMs), 3-D photogrammetry models, as well as scanning electron microscopy (SEM) and synchrotron X-ray computed tomography (CT) imaging of samples collected in the field
Earth Observing 1 (EO-1) and Landsat data are available from the U.S Geological Survey, and ASTER data are distributed by the Land Processes Distributed Active Archive Center (LP DAAC), located at the U.S Geological Survey Earth Resources Observation and Science Center (USGS/EROS), Sioux Falls, South Dakota, USA
Summary
Studies of hazards from silicic volcanic eruptions usually focus on explosive activity partly because effusive silicic eruptions are rare events. The emplacement of rhyolite lava flows has been previously associated with hazards such as explosions from their surface (Jensen, 1993; Castro et al, 2002), lava flow front collapse (Fink and Manley, 1987; Baum et al, 1989), and the potential generation of pyroclastic density currents (Fink and Kieffer, 1993) Of six such effusive eruptions in the 20th and 21st century (Katsui and Katz, 1967; Reynolds et al, 1980; Fierstein and Hildreth, 1992; Singer et al, 2008; Bernstein et al, 2013; Tuffen et al, 2013), three occurred at PuyehueCordón Caulle, southern Chile (in 1921–1922, 1960, and 2011–2012; Katsui and Katz, 1967; Lara et al, 2004; Singer et al, 2008; Tuffen et al, 2013). Throughout this study we consider a breakout to be a new, morphologically distinct region of lava flow advance, formed from the core of an otherwise stopped or slowed portion of the lava flow Such breakouts extend or widen the inundated area and uncertainties in where they will occur pose a challenge for forecasting lava inundation hazard. We present the first conceptual model for their formation and consider the processes involved
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
