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Exceptional Mobility of an Advancing Rhyolitic Obsidian Flow at CordÓN Caulle Volcano in Chile

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Exceptional Mobility of an Advancing Rhyolitic Obsidian Flow at CordÓN Caulle Volcano in Chile ARTICLE Received 7 Jun 2013 | Accepted 3 Oct 2013 | Published 1 Nov 2013 DOI: 10.1038/ncomms3709 Exceptional mobility of an advancing rhyolitic obsidian flow at Cordo´n Caulle volcano in Chile Hugh Tuffen1, Mike R. James1, Jonathan M. Castro2 & C. Ian Schipper3 The emplacement mechanisms of rhyolitic lava flows are enigmatic and, despite high lava viscosities and low inferred effusion rates, can result in remarkably, laterally extensive (430 km) flow fields. Here we present the first observations of an active, extensive rhyolitic lava flow field from the 2011–2012 eruption at Cordo´n Caulle, Chile. We combine high- resolution four-dimensional flow front models, created using automated photo reconstruction techniques, with sequential satellite imagery. Late-stage evolution greatly extended the compound lava flow field, with localized extrusion from stalled, B35 m-thick flow margins creating 480 breakout lobes. In January 2013, flow front advance continued B3.6 km from the vent, despite detectable lava supply ceasing 6–8 months earlier. This illustrates how efficient thermal insulation by the lava carapace promotes prolonged within-flow horizontal lava transport, boosting the extent of the flow. The unexpected similarities with compound basaltic lava flow fields point towards a unifying model of lava emplacement. 1 Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK. 2 University of Mainz, Institute of Geosciences, Becherweg 21, 55099 Mainz, Germany. 3 School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand. Correspondence and requests for materials should be addressed to H.T. (email [email protected]). NATURE COMMUNICATIONS | 4:2709 | DOI: 10.1038/ncomms3709 | www.nature.com/naturecommunications 1 & 2013 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms3709 ontrols on lava flow lengths and advance rates include lava observe the emplacement of rhyolitic lava, with both exogenous viscosity and yield strength, together with effusion rate and endogenous growth of a complex of domes and spines Cand topography1–3. As lava viscosity and yield strength between May 2008 and late 2009 (refs 17,18). The mean effusion 4 increase with melt silica content , high-silica lavas are generally rate of the crystal-poor, high-silica rhyolite (75 wt% SiO2) was considerably thicker, shorter and more slow-moving than basaltic 66 m3 s À 1 over the first 2 weeks and the total erupted lava lavas2,3,5,6, although crystal-poor rhyolitic lava may be volume was B0.8 km3. Notably, no extensive rhyolitic flow was significantly less viscous than crystal-rich andesite or dacite. generated, with lava extending o1 km from the vent18. Formation of an insulating crust reduces heat loss and Constraints on the evolution of extensive rhyolite lava flows significantly enhances lava mobility2,3. Crust formation is have been previously derived indirectly from analogue known to be important in basaltic lavas7, and extensive tube- experiments2, viscous flow models5,19 and thermal models13. fed lavas are commonly compound (consisting of multiple flow In contrast, the temporal evolution of frequently observed units8–9). Basaltic flow fields often advance through extrusion basaltic lava flow fields is well constrained7,10,20, and transitions from stalled flow fronts8,10. from simple to compound flow fields that consist of multiple Despite their high viscosity and inferred effusion rates of flow units are well documented8,9. In compound basaltic flows, o100 m3 s À 1, some rhyolitic lavas can flow for distances cessation of flow front advance triggers channel overflows and exceeding 30 km (ref. 11) and produce flows with volumes of breaches, or flow inflation and lava extrusion at flow fronts via up to 10–20 km3 (refs 12,13). Ogives indicate folding of B10 m- localized breakouts or squeeze-ups10. Long-term processes in thick surface crusts5, which may boost flow mobility by providing compound basaltic lava flow fields are therefore both vertical effective thermal insulation13. However, unlike basaltic flow (flow inflation and tumulus formation) and horizontal (creation models, existing models of rhyolitic flow emplacement focus on of breakouts). Some cross-compositional commonality in lava the inflation of single lava flow units once flow fronts have effusion and emplacement mechanisms has been identified, stalled14–16. including localized lava extrusion at dacitic lava flow margins21 Before the 2011–2012 eruption of Cordo´n Caulle, the 2008– that has a direct basaltic equivalent10,22. However, similarities 2009 eruption at Chaite´n had provided the only opportunity to between rhyolitic and basaltic emplacement are largely 72°14′ W 72°10′ W 72°06′ W N Cordón 1921–22 Caulle flow < 54 ka Cordón Caulle <173 ka 40°30′ S 1921–22 pumice 2011- 1960 flow 1960 pumice Puyehue 69-1 ka 40°34′ S Cordón Caulle 2011- lava Santiago Argentina Cordón Caulle 1960 Puyehue- Cordón Caulle 1921-22 Puyehue Cordón Chile Cordón Caulle <54 ka 314-96 ka 40° S Caulle Cordón Caulle <173 ka Puerto N Montt Puyehue 69-1 ka Puyehue 314-96 ka 1960 Atlantic Caldera margin Scarp 50° Ocean Pacific Ocean 70° 60° W Figure 1 | The Puyehue–Cordo´n Caulle volcanic complex. Highly simplified geological map of the Puyehue–Cordo´n Caulle volcanic complex, redrawn from Singer et al.24 and Lara et al.25 The Cordo´n Caulle volcanic system forms a 20-km-long and 4-km-wide ridge oriented NW-SE. The main fault scarps associated with the 1960 eruption25 are shown. Scale bar, 5 km in length. Inset: map indicating position of Cordo´n Caulle volcanic complex in southern Chile, redrawn from ref. 30. Scale bar, 100 km in length. 2 NATURE COMMUNICATIONS | 4:2709 | DOI: 10.1038/ncomms3709 | www.nature.com/naturecommunications & 2013 Macmillan Publishers Limited. All rights reserved. NATURE COMMUNICATIONS | DOI: 10.1038/ncomms3709 ARTICLE unquantified, and advance processes in rhyolitic lava flow fields and glass water contents are o0.2 wt% (J.M. Castro, manuscript are poorly understood. Our study addresses this issue by applying in preparation). quantitative three-dimensional (3D) imaging techniques23 to the Here we show that localized extrusion from the margins of the first extensive rhyolitic lava flow field to be observed in evolution, rhyolitic lava flow field at Cordo´n Caulle greatly extended the emplaced during the 2011–2012 eruption of Cordo´n Caulle, flow field during 18 months of flow evolution, and that this Chile. process continued for several months after the supply of lava at Puyehue–Cordo´n Caulle (40.5 °S) is a large basaltic-to-rhyolitic the vent ceased. Our results demonstrate how efficient thermal volcanic complex within the Andean Southern volcanic zone, insulation by the lava crust allows prolonged advance of 125 km northeast of Puerto Montt, Chile (Fig. 1). The 20-km- compound rhyolitic flow fields, and reveal unexpected common- long, NW-trending Cordo´n Caulle fissure complex (Fig. 1) has ality with processes at basaltic lava flow fields. produced B9km3 of rhyodacitic to rhyolitic lavas and pyroclastic deposits since 16.5 ka24. Cordo´n Caulle has produced two major historic eruptions, in 1921–1922; and 1960, in which 0.25– Results 0.3 km3 of rhyolitic magma (dense rock equivalent; 69.5–70.3 wt Ground-based imaging of the evolving lava flow field. Imaging 25 % SiO2) was erupted from r5.5 km-long fissures . of the northern lava flow field was conducted on 3–4 and An explosive eruption (0.2–0.4 km3 dense rock equivalent 10 January 2012. In 2012, vent activity was characterized by pyroclastic deposits) commenced on 4 June 2011, with a 27-h- semicontinuous ash jetting punctuated by Vulcanian-like blasts, long initial Plinian phase (r15 km plume height)26,27. Ash plume creating a 2-km-high ash plume32. Visual observations and digital heights had decreased to 2–5 km by January 2012, when our photographs for 3D reconstruction were collected during observations were collected, and ash emissions ended in June B1-km-long traverses of a ridge directly overlooking the 2012. A 50-m-wide, 150-m-long lava flow was first observed on northern flow margin (Fig. 2a). See Methods for details of the 20 June 2011 (ref. 28). Although lava outflow at the vent arguably automated photo reconstruction techniques employed. We noted ended on 15 March 2012, when tremors ceased29, the flow field structural and textural features typical of documented obsidian continued to evolve into January 2013, when we witnessed flows in the lava, such as ogives on the flow surface5,6,16,19 and rockfall at an advancing breakout. Lava flow field evolution was zones of variably vesicular glassy lava14–16, including coarsely captured30 by the Earth Observing-1 spacecraft (Fig. 2). The vesicular pumice. initial lava discharge rate was estimated31 to be 20–60 m3 s À 1 and On 4 January 2012, the lava flow front was characterized by the discharged lava volume was B0.4 km3 by April 2012 (C. Silva two dominant facies (Fig. 3). Predominant rubbly lava was B30– Parejas, personal communication). Lava whole-rock composition 40 m thick and mantled by unstable talus. Angular, rotated lava 26 is rhyolitic , with 69.8–70.1 wt% SiO2 and 7.8 wt% Na2O þ K2O, blocks ranged from tens of centimetres to several metres across. ab 3b Northern 3a flow field 4 Inactive 3 2 11 January 1 2013 Rio Nilahue 40°31′ S Flow features Breakout lobe 13/01/13 Ogive 01/11/12 N Vent Strike-slip 26/01/12 shear zone N 09/10/11 Active 11 January 2013 Active 40°32′ S 11 January Not visible in 2013 09/10/11 and 26/01/12 images Southern flow field 72°10′ W 72°09′ W 72°08′ W Figure 2 | Overview of lava flow field evolution.
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