Characterization of tephra deposits with limited exposure: the example of the two largest explosive eruptions at Nisyros volcano (Greece)

Abstract

Explosive eruptions associated with tephra deposits that are only exposed in proximal areas are difficult to characterize. In fact, the determination of physical parameters such as column height, mass eruption rate, erupted volume, and eruption duration is mainly based on empirical models and is therefore very sensitive to the quality of the field data collected. We have applied and compared different modeling approaches for the characterization of the two main tephra deposits, the Lower Pumice(LP) and Upper Pumice (UP) of Nisyros volcano, Greece, which are exposed only within 5 km of the probable vent. Isopach and isopleth maps were compiled for two possible vent locations (on the north and on the south rim of the caldera), and different models were applied to calculate the column height, the erupted volume, and the mass eruption rate. We found a column height of about 15 km above sea level and a mass eruption rate of about 2×10^7 kg/s for both eruptions regardless of the vent location considered. In contrast, the associated wind velocity for both UP and LP varied between 0 and 20 m/s for the north and south vent, respectively. The derived erupted volume for the south vent (considered as the best vent location) ranges between 2 and 27×10^8 m3 for the LP and between 1 and 5×10^8 m3 for the UP based on the application of four different methods (integration of exponential fit based on one isopach line, integration of exponential and power-law fit based on two isopach lines, and an inversion technique combined with an advection–diffusion model). The eruption that produced the UP could be classified as subplinian. Discrepancies associated with different vent locations are smaller than the discrepancies associated with the use of different models for the determination of erupted mass, plume height, and mass eruption rate. Proximal outcrops are predominantly coarse grained with ≥90 wt% of the clasts ranging between −6phi and 0phi. Theassociated total grainsize distribution is considered to result from a combination of turbulent fallout from both the plume margins and the umbrella region, and as a result, it is fines-depleted. Given that primary deposit thickness observed on Nisyros for both LP and UP is between 1 and 8 m, if an event of similar scale were to happen again, it would have a significant impact on the entire island with major damage to infrastructure, agriculture, and tourism. Neighboring islands and the continent could also be significantly affected

Inverse differentiation pathway by multiple mafic magma refilling in the last magmatic activity of Nisyros Volcano, Greece

“…Several papers have been recently published on the Nisyros geology and volcanological evolution (Davis 1967;Di Paola 1974;Vougioukalakis 1993;Lodise 1987;Gansecki 1991;Limburg and Varekamp 1991;Seymour and Vlassopoulos 1992;Francalanci et al 1995Francalanci et al , 2007Volentik et al 2002Volentik et al , 2005aBuettner et al 2005;Longchamp et al 2011) generally recognizing that the volcanic activity of Nisyros can be subdivided into two distinct phases, as firstly reported by Di Paola (1974): (1) pre-caldera activity, building up the edifice by lavas and pyroclastic products (ca. 100-55 ka) and ranging in composition from basaltic-andesites to rhyolites; (2) a second phase (between ca.…”

“…The second phase was characterized by two distinct and destructive events of Plinian and sub-Plinian eruption (Limburg and Varekamp 1991;Volentik et al 2002;Longchamp et al 2011) associated with caldera collapses and both followed by the emplacement of voluminous lava flows and domes. The first Plinian eruption formed the pyroclastic deposits of the Lower Pumice unit (andesitic and rhyolitic in composition) and a consequent caldera depression, which was partially refilled by the next rhyolitic Nikia lavas (with basaltic-andesite enclaves).…”

A mineral and cumulate perspective to magma differentiation at Nisyros volcano, Aegean arc

“…These porphyritic (rhyo)dacites are characterised by the conspicuous presence of mafic enclaves with a large range in phenocryst compositions and disequilibrium textures, which are indicative of magma mingling (Braschi et al 2012(Braschi et al , 2014Zouzias and St Seymour 2014). Lava flow 7 (LF7), underlying the Lies tuff cone, is the oldest studied enclave-bearing porphyritic dacite, followed by the Emborio domes (EMB) and the calderaforming Lower and Upper Pumice eruptions (LP and UP, respectively; Limburg and Varekamp 1991; Longchamp et al 2011). The latter are separated by the emplacement of a ca.…”

Vhub: a knowledge management system to facilitate online collaborative volcano modeling and research

“…It can be used for civil protection purposes, such as giving public warnings and planning mitigation measures (Connor et al 2001;Volentik et al 2009), as a research tool for studying eruptions past and present (Johnston et al 2012;Biass and Bonadonna 2011;Longchamp et al 2011;Connor and Connor 2006;Volentik et al 2010), or as an educational tool for volcanology, numerical modeling, or quantitative literacy (Courtland et al 2012).…”