Loki is the most powerful volcano in the Solar System. It has been observed to be in continuous though variable activity since 1979. Synthesis of more than a decade of groundbased data suggests that Loki eruptions are cyclic, with a 540 day period. Application of a simple lava cooling model to temperatures in Loki Patera, and eruption start and end times, implies that brightenings are due to a resurfacing wave propagating across the patera. The data are most consistent with lava lake overturn, but resurfacing by lava flows cannot be ruled out. A porosity gradient in the lake crust could cause lava lake overturn to occur periodically on the timescale observed.
Lunar pyroclastic beads are interpreted to represent primitive magmas derived from great depths and rapidly erupted to the surface in explosive events. However, a detailed mechanism for gas generation at great depth and rapid magma transport to the surface has not yet been described. Furthermore, the pyroclastic beads are not petrogenetically related to basalts erupted near the sampling sites. We propose a model in which these conundrums are resolved through gas build‐up in a low‐pressure micro‐environment near the tip of a magma‐filled crack (dike) propagating rapidly from the magma source depth to the surface. The gas rich region consists of a free gas cavity overlying a foam extending vertically for ∼20 km. Eruption of the foam results in the widespread emplacement of unfractionated pyroclastic beads. Subsequent ascent of the underlying gas‐free picritic magma is unlikely to occur, perhaps accounting for the lack of sampled eruptive equivalents.
[1] Volcanic plumes deposit magmatic pyroclasts and SO2 frost on the surface of Io. We model the plume activity detected by Galileo at the Pillan and Pele sites from 1996 to 1997 assuming that magmatic eruptions incorporate liquid SO2 from near-surface aquifers intersecting the conduit system and that the SO2 eventually forms a solid condensate on the ground. The temperature and pressure at which deposition of solid SO2 commences in the Ionian environment and the radial distance from the volcanic vent at which this process appears to occur on the surface are used together with observed vertical heights of plumes to constrain eruption conditions. The temperature, pressure, and density of the gas–magma mixtures are related to distance from the vent using continuity and conservation of energy. Similar eruption mass fluxes of order 5 × 107 kg s−1 are found for both the Pillan and the Pele plumes. The Pele plume requires a larger amount of incorporated SO2 (29–34 mass %) than the Pillan plume (up to ∼6 mass %). Implied vent diameters range from ∼90 m at Pillan to ∼500 m at Pele. The radial extents of the optically dense, isothermal, incandescent parts of the eruption plumes immediately above the vents are ∼100 m at Pillan and ∼1300 m at Pele. Gas pressures in the vents are ∼20 kPa at Pillan and ∼2 kPa at Pele and the eruption conditions appear to be supersonic in both cases, though only just so at Pele.
Plinian air-fall deposits and ignimbrites are the principal products of explosive eruptions of high viscosity magma. In this paper, the flow of gas/pyroclast dispersions and high viscosity magma through various magma chamber/conduit/vent geometries is considered. It is argued that after the first few minutes of an eruption magma fragmentation occurs at a shallow depth within the conduit system. Gas pressures at the fragmentation level are related to exsolved gas contents by consideration of the exsolution mechanism.
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