Bull Volcanol (2016) 78:57 DOI 10.1007/s00445-016-1053-0 RESEARCH ARTICLE Ash production and dispersal from sustained low-intensity Mono-Inyo eruptions Benjamin A. Black1,2, & Michael Manga1 & Benjamin Andrews3 Received: 23 January 2016 /Accepted: 18 July 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Recent rhyolitic volcanism has demonstrated that Introduction prolonged low-intensity ash venting may accompany effusive dome formation. We examine the possibility and some conse- The Mono-Inyo craters are a sickle-shaped chain of rhyolitic quences of episodes of extended, weak ash venting at the domes and craters that extends to the northwest of the Long rhyolitic Mono-Inyo chain in Eastern California. We describe Valley Caldera in California (Sieh and Bursik 1986;Bursik ash-filled cracks within one of the youngest domes, Panum and Sieh 1989;Hildreth2004). Eruptions have occurred in the Crater, which provide a textural record of ash venting during recent past, including eruptions along the Mono-Inyo chain dome effusion. We use synchrotron-based X-ray computed ∼700 years ago (Sieh and Bursik 1986) and at Paoha Island tomography to characterize the particles in these tuffisites. ∼200 years ago (Bailey 1989), and the majority of eruptions Particle sizes in well-sorted tuffisite layers agree well with have occurred within the past 20 ka. The total erupted volume grain size distributions observed during weak ash venting at of the Mono-Inyo craters is ∼5.8–9.3 km3 (Miller 1985;Sieh Soufrière Hills Volcano, Montserrat, and yield approximate and Bursik 1986;Hildreth2004). Their recent activity—com- upper and lower bounds on gas velocity and mass flux during bined with their location (∼40 km east of Yosemite, CA, and the formation of those layers. We simulate ash dispersal with ∼370 km northwest of Las Vegas, NV), rhyolitic composition, Ash3d to assess the consequences of long-lived Mono-Inyo and propensity for explosive eruptions (Sieh and Bursik ash venting for ash deposition and the accompanying volcanic 1986)—renders the Mono-Inyo craters one of the most potent hazards. Our results highlight the sensitivity of large-scale volcanic hazards in CA, USA (Hill et al. 1997). outcomes of volcanic eruptions to small-scale processes. The Chaitén eruption of 2008–2009 and the Cordón Caulle eruption of 2011 in Chile presented the first opportunities to employ modern geological and geophysical tools to observe a Keywords Mono-Inyo eruptions . Rhyolitic volcanism . Ash rhyolitic effusive eruption in progress (Lara 2009;Wattetal. venting . X-ray computed tomography . Ash3d 2009; Alfano et al. 2011; Bernstein et al. 2013; Pallister et al. 2013; Tuffen et al. 2013; Castro et al. 2013;Castroetal.2014; Schipper et al. 2013). One of the most surprising aspects of the Editorial responsibility: C. Bonadonna Chaitén eruption was the sustained, low-intensity ash produc- tion that followed the initial Plinian phase (Lara 2009;Carn * Benjamin A. Black et al. 2009). After partial dome collapse on February 19, 2009, ash [email protected] production and low-altitude injection continued until the end of the eruption in late 2009 and coincided with gradual dome 1 Department of Earth and Planetary Science, University of California, growth (Lara 2009;Carnetal.2009; Pallister et al. 2013). Berkeley, CA 94720, USA During the June 2011 eruption at Cordón Caulle, the initial 2 Department of Earth and Atmospheric Science, City College, City climactic phase similarly transitioned to weeks of lower- University of New York, New York, NY, USA intensity ash venting accompanied by a weak plume 3 Department of Mineral Sciences, Smithsonian Institution, (Bonadonna et al. 2015a; Pistolesi et al. 2015). Ash-filled Washington, DC, USA cracks (called tuffisite) are abundant within blocks and bombs 57 Page 2 of 13 Bull Volcanol (2016) 78:57 at Chaitén and at Cordón Caulle and have been interpreted as (Miller 1985; Sieh and Bursik 1986). Even younger volcanism evidence of shear fracturing and as pathways for degassing may have taken place in the past 200 years at Paoha Island in during dominantly effusive phases (Castro et al. 2012; Mono Lake (Bailey 1989). Because the Mono-Inyo crater Schipper et al. 2013;Castroetal.2014;Saubinetal.2016; chain is outside the ring-fault zone of Long Valley Caldera, Kendrick et al. 2016). and because eruption rates and seismic tomography suggest In this work, we document the distribution of tuffisite-filled that the main Long Valley magma chamber may be moribund, cracks at Panum Crater that contain ash produced during the Hildreth (2004) has argued that the Mono-Inyo craters origi- North Mono eruptions <700 years ago (Sieh and Bursik 1986). nate from a separate magmatic system that largely does not tap We characterize the tuffisite using thin sections and X-ray the chamber that formed the Bishop Tuff. Thus, while a uni- computed tomography (XRCT). We suggest that, like the fied set of processes have likely encouraged mantle melting tuffisites from Chaitén and Cordón Caulle, these features and basaltic intrusion beneath the Long Valley region, these may record past low-intensity ash production during dome basaltic melts have focused in several distinct loci, most re- effusion in the Mono-Inyo region. Estimates of mass flux cently beneath the Mono-Inyo chain (Hildreth 2004). Crustal from grain size distribution are consistent with protracted, melting probably feeds the dominantly rhyolitic Mono-Inyo unsteady venting. We use Ash3d (Schwaiger et al. 2012; eruptions, while range-front faulting controls the distribution Mastin et al. 2013) to simulate the transport and deposition of volcanism (Bursik and Sieh 1989). of ash from a small, sustained, rhyolitic Mono-Inyo eruption. During the period of activity in the fourteenth century, The goal of these simulations is to assess the consequences of within a span of several years, a series of eruptions took place ash venting for the Long Valley region and to explore quali- at both the northern and southern extremities of the Mono- tative differences between ash dispersal during sustained low- Inyo chain (Miller 1985;SiehandBursik1986). At the south- intensity venting versus more explosive eruptions. We show ern end of the chain, the Inyo dike triggered formation of that for a given total eruption volume, as the eruption duration multiple phreatic craters and rhyolitic vents (Miller 1985; increases and column heights decrease, the ash dispersal pro- Mastin and Pollard 1988;Mastin1991; Nawotniak and cess is increasingly sensitive to topography and also samples a Bursik 2010). At the northern end of the chain, an initial larger range of wind directions (diminishing the spatial unpre- sub-Plinian phase gave way to pyroclastic flows and surges, dictability of cumulative ashfall). The patterns of ash dispersal followed by extrusive formation of lava flows and domes from sustained, weak ash venting are fundamentally different (with a total extrusive volume of ∼0.44 km3 dense rock equiv- from dispersal from short-lived, vigorous eruption columns. alent; Sieh and Bursik 1986). These results agree with observations and modeling of weak, While several vents contributed to this activity, Panum wind-affected plumes during eruptions at Mt. Etna, Cordón Crater has been described in particular detail. Panum Crater Caulle, and elsewhere (Scollo et al. 2007;Barsottietal.2010; (Fig. 1) is situated near the southern edge of Mono Lake; the Scollo et al. 2013; Bonadonna et al. 2015a; Bonadonna et al. crater is surrounded by a tephra ring (with angular ash, lapilli, 2015b; Pistolesi et al. 2015). and rare small blocks), and within the crater, there are several small rhyolitic plugs known as North Dome, South Dome, East Dome, and Southwest Dome (Sieh and Bursik 1986). Geologic background The excavation of the crater postdates the North Mono Plinian ashfalls and was accompanied by a series of pyroclas- The Long Valley region is situated at the boundary between tic flows and surges and at least one block-and-ash flow (Sieh the Sierra Nevada and the Basin and Range Province (Fig. 1) and Bursik 1986). Radiocarbon dates from charred wood frag- and has hosted a rich history of magmatism. Beginning ments within Panum deposits yield a weighted average date of ∼4.5 Ma, Basin and Range extension promoted decompres- 1324–1365 A.D. (Sieh and Bursik 1986). sion melting in the underlying mantle (Hildreth 2004). The The thickest ashfall deposits from Mono-Inyo eruptions are ensuing magmatism included mafic and dacitic eruptions that often locally well preserved and have been described by Sieh ultimately gave way to the 2.2–1.4 Ma Glass Mountain rhyo- and Bursik (1986), Nawotniak and Bursik (2010), and Bursik lites (Metz and Mahood 1985;Bailey1989;Bailey2004). The et al. (2014). As described by these authors, many past explo- eruption of the 600 km3 Bishop Tuff 767.1 ± 0.9 ka (Crowley sive episodes have produced Plinian or sub-Plinian columns et al. 2007) spanned only ∼6 days (Wilson and Hildreth 1997) that exceed the column heights of 1–7.7 km we consider here. and formed the Long Valley Caldera. Following the eruption The durations of these explosive events may be only hours to of the Bishop Tuff and the emplacement of the postcaldera days (e.g., Nawotniak and Bursik 2010), and some deposits Early Rhyolite (Bailey 2004), the pace of magmatism in the are highly elongated (e.g., Bursik et al. 2009). Short-lived Long Valley region declined markedly (Hildreth 2004). plumes may have reached up to 20 km altitude (Nawotniak Mono-Inyo volcanism initiated ∼50 ka, and the most recent and Bursik 2010). The premise of the present work is that in Mono-Inyo eruptions occurred in the fourteenth century addition to these explosive episodes, low-intensity ash Bull Volcanol (2016) 78:57 Page 3 of 13 57 Fig. 1 a Map of Panum Crater, simplified from Sieh and Bursik (1986) numbers.