Tracking Formation of a Lava Lake From Ground and Space: Masaya Volcano (Nicaragua), 2014–2017

Abstract

A vigorously degassing lava lake appeared inside the Santiago pit crater of Masaya volcano (Nicaragua) in December 2015, after years of degassing with no (or minor) incandescence. Here we present an unprecedented‐long (3 years) and continuous volcanic gas record that instrumentally characterizes the (re)activation of the lava lake. Our results show that, before appearance of the lake, the volcanic gas plume composition became unusually CO2 rich, as testified by high CO2/SO2 ratios (mean: 12.2 ± 6.3) and low H2O/CO2 ratios (mean: 2.3 ± 1.3). The volcanic CO2 flux also peaked in November 2015 (mean: 81.3 ± 40.6 kg/s; maximum: 247 kg/s). Using results of magma degassing models and budgets, we interpret this elevated CO2 degassing as sourced by degassing of a volatile‐rich fast‐overturning (3.6–5.2 m3 s−1) magma, supplying CO2‐rich gas bubbles from minimum equivalent depths of 0.36–1.4 km. We propose this elevated gas bubble supply destabilized the shallow (<1 km) Masaya magma reservoir, leading to upward migration of vesicular (buoyant) resident magma, and ultimately to (re)formation of the lava lake. At onset of lava lake activity on 11 December 2015 (constrained by satellite‐based MODIS thermal observations), the gas emissions transitioned to more SO2‐rich composition, and the SO2 flux increased by a factor ∼40% (11.4 ± 5.2 kg/s) relative to background degassing (8.0 kg/s), confirming faster than normal (4.4 versus ∼3 m3 s−1) shallow magma convection. Based on thermal energy records, we estimate that only ∼0.8 of the 4.4 m3 s−1 of magma actually reached the surface to manifest into a convecting lava lake, suggesting inefficient transport of magma in the near‐surface plumbing system.

Satellite Geodesy Captures Offset Magma Supply Associated With Lava Lake Appearance at Masaya Volcano, Nicaragua

“…It is, however, important to note that our modeled volume changes are not necessarily the same as the "excess" magma volume modeled from the gas measurements; that is, the volume of magma intruded is a factor of compressibility of the chamber, the magma already in the chamber, and the exsolved gases (Johnson et al, 2000;Rivalta & Segall, 2008;Segall, 2010). The results from the gas and geodetic data sets, coupled with the emergence of the lava lake in 2015, support the hypothesis that Masaya has cycles of degassing crises every 10-20 years, with the most recent degassing crisis prior to 2015 starting in 1993 (Aiuppa et al, 2018;Murray et al, 2017;Rymer et al, 1998Rymer et al, , 2017.…”

“…The appearance of a new lava lake in 2015 in conjunction with the observed inflation suggests magma supply into the magma plumbing system at Masaya. This hypothesis is supported by the observation of a dramatic increase in the CO 2 levels in mid‐ to late‐November 2015, about 2 weeks prior to the lava appearance (Aiuppa et al, ). Our results suggest a volume increase of ∼0.0042 km 3 , which is lower than the ∼0.0072–0.0082 km 3 estimated “excess” magma volume degassed between November 2015 and February 2016 (Aiuppa et al, ).…”

“…This hypothesis is supported by the observation of a dramatic increase in the CO 2 levels in mid‐ to late‐November 2015, about 2 weeks prior to the lava appearance (Aiuppa et al, ). Our results suggest a volume increase of ∼0.0042 km 3 , which is lower than the ∼0.0072–0.0082 km 3 estimated “excess” magma volume degassed between November 2015 and February 2016 (Aiuppa et al, ). It is, however, important to note that our modeled volume changes are not necessarily the same as the “excess” magma volume modeled from the gas measurements; that is, the volume of magma intruded is a factor of compressibility of the chamber, the magma already in the chamber, and the exsolved gases (Johnson et al, ; Rivalta & Segall, ; Segall, ).…”

“…Seismic measurements were only made again from 18 December due to lightning destroying the transmission equipment and the seismic station digitizer on 27 September 2015 (INETER, ). Three years of continuous gas measurements (Aiuppa et al, ) show a sharp increase in the CO 2 /SO 2 ratio in mid‐November, followed by a drop between 26 and 27 November 2015. These gas observations can be explained by a new pulse of gas‐rich magma into the magma plumbing system about 2 weeks prior to visual observations of incandescence at Santiago (Aiuppa et al, ).…”

“…Three years of continuous gas measurements (Aiuppa et al, ) show a sharp increase in the CO 2 /SO 2 ratio in mid‐November, followed by a drop between 26 and 27 November 2015. These gas observations can be explained by a new pulse of gas‐rich magma into the magma plumbing system about 2 weeks prior to visual observations of incandescence at Santiago (Aiuppa et al, ). On 9 December, an earthquake of magnitude 3.0 occurred 2 km SE of Masaya caldera, near the city of Masaya (INETER, ).…”