Thermal signature, eruption style, and eruption evolution at Pele and Pillan on Io

Abstract

It has proved possible to track thermal emission from a number of volcanic centers over several orbits to enable individual eruptions to be observed as they start, build, and wane. This has yielded new information about the magma temperature, eruption style, and evolution of these volcanic centers. We show how, with sufficient temporal and wavelength coverage, it is possible to constrain style of eruption from the evolution of thermal emission spectra at two different hot spots, initially using a two-temperature fit to NIMS data to determine temperatures, areas, and total thermal output. Using a silicate cooling model [Davies, 1996], we show that it is possible to constrain magma temperature from the combined NIMS-SSI data and to determine rates of areal coverage. Finally, the eruption styles are compared with their terrestrial counterparts. 2.Galileo NIMS and SSI Observations of Io

Photochemistry of a Volcanically Driven Atmosphere on Io: Sulfur and Oxygen Species from a Pele-Type Eruption

“…Their model can represent the true state of the volcanic gases erupting at Pele if the vapor can be assumed to be in thermochemical equilibrium in a high-temperature volcanic conduit and/or lava lake before eruption and if the gas chemistry is quenched rapidly in the vicinity of the vent during the eruption (e.g., Zolotov and Fegley 1998a. The Pele magma temperature of ∼1440 K derived by Zolotov and Fegley (2000a) is consistent with the temperatures inferred from Galileo infrared and visible observations of the Pele hot spot (e.g., McEwen et al 1998b, Lopes-Gautier et al 1999, Davies et al 1999. When combined with information on the S 2 /SO 2 ratio in the Pele plume , the vent pressures can also be constrained; Zolotov and Fegley (2000a) determine that vent pressures at Pele lie within the range (0.4-2) × 10 −5 bars.…”

“…If photochemical processing of the plume vapors occurs on very short time scales relative to the lifetime of fresh volcanic gas that is being supplied to the plume, then the above assumption will be incorrect, and the magma temperature or vent pressure derived for the Pele volcanic region from the thermochemical equilibrium calculations could be suspect. Note, however, that based on the observed plume abundances and thermochemical equilibrium calculations, Zolotov and Fegley (2000a) derive a magma temperature (∼1440 K) that is consistent with independent Galileo infrared and visible observations of minimum temperatures of ∼1280-1400 K for the hottest component observed in the Pele region (McEwen et al 1998bDavies et al 1999Davies et al , 2000a, and both the temperature and oxygen fugacity (3.3 log f O 2 units below the Ni-NiO buffer) derived by Zolotov and Fegley (2000a) are consistent with the possible presence of Mg-rich silicates (orthopyroxene) in pyroclastic deposits around Pele (Geissler et al 1999a(Geissler et al , 2000.…”

Silicate Cooling Model Fits to Galileo NIMS Data of Volcanism on Io

“…The shapes of the G1 hot spot spectra do not exhibit the thermal emission at short wavelengths (less than 2 µm) that would be expected from a large, turbulently emplaced flow. Post-G1 observations of Pele and Pillan (see Davies et al 1999) show extensive emission at short wavelengths and are not well-fitted with a "single-lobe" model. These data are indicative of a more complex and different style of emplacement from that implied by G1INNSPEC01 analysis.…”

“…Constraints can be applied. We have seen that a two-temperature fit to Zamama data implies a magma temperature of at least 1350 K. Post-G1 SSI dual-filter observations yielded best-fit single temperatures from 940 to 1675 K for the hottest components of hot spots seen in eclipse (McEwen et al 1998a,b), and fitting the silicate cooling model (using a range of initial magma liquidus temperatures) to a combined NIMS-SSI Pillan dataset from orbit C9 produced an implied magma temperature of at least 1870 K (Davies et al 1999), too high a temperature for basalt. Unfortunately, such dual-filter data were not available for the NIMS G1 hot spots.…”

“…The criteria for selecting a hot spot as being "major" were given in Lopes-Gautier et al as: (1) a positive slope of the spectrum between 3.5 and 5 µm and (2) an emission at local maximum greater than that of all surrounding pixels. Since the analysis of the G1 data, and in light of subsequent observations (especially in orbit C9), the first condition has had to be modified slightly to take into account other hot spots, most notably at Pele and Pillan, that had spectra with a negative slope between 3.5 and 5 µm due to the peak of thermal emission shifting to shorter wavelengths than that seen in G1 data (Davies et al, 1999). Table I lists the hot spots analyzed, together with their positions and emission angles as measured from the local planetary normal.…”