Magmatic gas percolation through the old lava dome of El Misti volcano

Abstract

The proximity of the major city of Arequipa to El Misti has focused attention on the hazards posed by the active volcano. Since its last major eruption in the fifteenth century, El Misti has experienced a series of modest phreatic eruptions and fluctuating fumarolic activity. Here, we present the first measurements of the compositions of gas emitted from the lava dome in the summit crater. The gas composition is found to be fairly dry with a H 2 O/SO 2 molar ratio of 32 ± 3, a CO 2 / SO 2 molar ratio of 2.7 ± 0.2, a H 2 S/SO 2 molar ratio of 0.23 ± 0.02 and a H 2 /SO 2 molar ratio of 0.012 ± 0.002. This magmatic gas signature with minimal evidence of hydrothermal or wall rock interaction points to a shallow magma source that is efficiently outgassing through a permeable conduit and lava dome. Field and satellite observations show no evolution of the lava dome over the last decade, indicating sustained outgassing through an established fracture network. This stability could be disrupted if dome permeability were to be reduced by annealing or occlusion of outgassing pathways. Continued monitoring of gas composition and flux at El Misti will be essential to determine the evolution of hazard potential at this dangerous volcano.

Spatio-Temporal Relationships between Fumarolic Activity, Hydrothermal Fluid Circulation and Geophysical Signals at an Arc Volcano in Degassing Unrest: La Soufrière of Guadeloupe (French West Indies)

“…Each instrument also includes a relative humidity sensor (Galltec, range: 0-100% Rh, accuracy: ± 2%), coupled with a temperature sensor (range: −30-70 • C, resolution: 0.01 • C) and atmospheric pressure (P atm ) sensor, all fixed externally, that permit to determine the concentration of water vapor (ppmv). The latter was obtained by combining the sensor readings of Rh% and P atm following the procedure described in Moussallam et al [47]. H 2 O determination with these external sensors allowed us to circumvent the potential influence of steam condensation in the MultiGAS inlet tubing and, therefore, to avoid underestimating the measured water/gas ratios.…”

Volcanic gas emissions and degassing dynamics at Ubinas and Sabancaya volcanoes; implications for the volatile budget of the central volcanic zone

“…Similar systems have now been successfully deployed at many volcanoes (e.g. Aiuppa et al, 2011Aiuppa et al, , 2012Aiuppa et al, , 2014Aiuppa et al, , 2015Moussallam et al, 2012Moussallam et al, , 2014Moussallam et al, , 2016Moussallam et al, , 2017 and the system used here is the same as Moussallam et al (2016). All sensors were calibrated in the laboratory in late October 2015 with target gases of known amount.…”

Insights into the recurrent energetic eruptions on Awu, one of the deadliest volcano on earth

“…Assuming the above results are representative then H2O, CO2, H2S, and H2 emission rates would be 5800 t/d, 2600 t/d, 340 t/d and 0.1 t/d respectively. The gas equilibrium temperature obtained by resolving together the SO2/H2S vs. H2/H2O redox equilibria (see methodology in Aiuppa et al, 2011;Moussallam et al, 2017) is circa 380 °C (Bani et al, submitted) Thermal infrared recording from the rim highlights two main heated surfaces in Awu's crater, but both are located to the northern part of the lower crater wall, next to the lava dome (IR2, IR3, Fig.3). It is also evident from these thermal results that the lower crater wall around the dome is much hotter than the lava dome itself.…”

“…The current lava dome on Awu has developed 16 years ago, just after the 2004 eruption. T he prevalence of H2S over SO2, the low SO2 emission budget of 13 t/d and the low equilibrium temperature of circa 380 °C obtained by resolving together the SO2/H2S vs. H2/H2O redox equilibria (see methodology in Aiuppa et al, 2011;Moussallam et al, 2017) indicate that the current activity on Awu is sustained by a degassed magma. Hence, assuming that the processes that lead to vigorous eruption will repeat themselves then the subsurface volcanic system has to develop more than 3.1 MPa of pressure (Pressure (Pa) = F/Area (m 2 ); F (N) = masse (kg) x 9.8 (m/s 2 ); density of 2700 kg/m 3 ) to destabilized the 3.5x10 10 kg of lava dome.…”