Emplacing a Cooling-Limited Rhyolite Lava Flow: Similarities with Basaltic Lava Flows

Abstract

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.

Emplacement of the Rocche Rosse rhyolite lava flow (Lipari, Aeolian Islands)

“…Crusts influence lava flow growth (Griffiths and Fink 1992;Fink and Griffiths 1998), and thermally insulate the flow, facilitating prolonged mobility and advance (Swanson 1973;Manley 1992;Fink and Griffiths 1998;Keszthelyi and Self 1998;Harris and Rowland 2009;Tuffen et al 2013). This has been previously observed in dacitic lava flow emplacement at Santiaguito (Harris et al 2002(Harris et al , 2004, and active rhyolitic flow emplacement at Puyehue-Cordón Caulle Magnall et al 2017).…”

“…Pinkerton and Sparks 1978;Lipman and Banks 1987;Self et al 1997;Calvari and Pinkerton 1999;Cashman et al 1999;Kilburn 2000;Jerram 2002, Passey andBell 2007), such studies of more silicic lava flows are comparatively few (e.g. Fink 1983;de Silva et al 1994;Fujii and Nakada 1999;Uia et al 1999;Castro et al 2002;Harris et al 2002;Cioni and Funedda 2005;Tuffen et al 2013;Magnall et al 2016Magnall et al , 2017Latutrie et al 2017). This is due in part to a lack of observations of active flows.…”

“…Such structures are often evident and have been studied in viscous intermediate lava flows (e.g. Cerro Chao, ChileFink 1980b;de Silva et al 1994; Puy de Cliergue, France- Latutrie et al 2017;San Pietro, Sardinia-Cioni and Funedda 2005;Santiaguito, Guatemala-Harris et al 2002, and other rhyolitic lava flows worldwide (Fink 1980a(Fink , b 1983Manley and Fink 1987;Carn et al 2009;Lara 2009;Bernstein et al 2013;Pallister et al 2013;Tuffen et al 2013;Magnall et al 2017).…”

“…Since 2008, real-time observations of active rhyolitic flow and dome emplacement at the Chilean volcanoes of Chaitén (Carn et al 2009;Lara 2009;Bernstein et al 2013;Pallister et al 2013) and Puyehue-Cordón Caulle Schipper et al 2013;Tuffen et al 2013;Bertin et al 2015;Farquharson et al 2015;Magnall et al 2017) have further developed our knowledge of rhyolitic lava emplacement. The Cordón Caulle eruption is an example of a flow that moved away from the vent, while Chaitén was a domeforming eruption.…”

“…These resulted from multiple flow paths (flow directions of areas of active dome growth) within the lava dome, and different extrusion rates (Carn et al 2009;Lara 2009;Bernstein et al 2013;Pallister et al 2013). Morphological observations of the 2011-2012 Cordón Caulle eruption highlight the role of thermal insulation by a surface crust in prolonging flow-horizontal transport, channelled flow, surface crust formation, development of breakout lobes and flow frontal stalling Schipper et al 2013;Tuffen et al 2013;Bertin et al 2015;Magnall et al 2017). In these studies, comparisons are made to basaltic lava flow fields, with common controlling mechanisms that work towards a unified model of effusive eruptions Schipper et al 2013;Tuffen et al 2013;Bertin et al 2015;Magnall et al 2017).…”