The evidence of bodies of elemental sulfur (S ) beneath acid crater lakes at the summit of composite active volcanoes has been recognized several decades ago (Oppenheimer and Stevenson, 1989; Christenson and Woods, 1993). But S accumulation was already hypothesized a century ago at Kusatzu Shirane (Japan) based on the observation of sulfur spherules floating on its crater-lake (Ohashi, 1919). Since these pioneering works, other studies have focused on understanding key aspects of molten sulfur bodies, considered a feature unique of volcanic lakes. Instead, it is reasonable to assume that S bodies occur in several volcanic settings because a) several reactions may lead to S deposition from S-bearing gases, and b) crater-lakes, surface expressions of hydrothermal systems, are transient features. The scrubbing of several magmatic gases, some of which critical for volcano monitoring, has been attributed to ground/surface waters (Symonds et al. 2001). Nevertheless, gas scrubbing could reflect viscosity variations of impure S within hydrothermal systems. Industrial experiments indicated that impurities (organics, H2S, ammonia, HCl, HF, HBr, HI) hinder S polymerization at T ≥ 160ºC, allowing viscosity to remain low for a long time depending on the maximum T achieved and heating rates (Bacon and Fanelli, 1943). However, a prolonged heating destroys the viscosity-modifying substances (e.g. H2Sx formed by reactions with organics, H2S) and dramatic S viscosity increases occur after a certain number of heating and cooling cycles. A prolonged boiling of S with organics was observed to release H2S, following H2Sx disruption. Some gases (e.g. SO2) do not affect S viscosity. In volcanic environments, non-reactive species (e.g. SO2, CO2) could, therefore, escape under S low viscosity regimes. Also, halogens absence in gas emissions could be caused by their participation in reactions within S-layers causing its viscosity to remain low. More data are needed to validate the hypothesis stated above. References Bacon RF, Fanelli R, J Am Chem Soc 65, 639-648 (1943). Christenson, BW, Wood CP, Bull Volcan 55, 547-565 (1993). Ohashi R, J. Akita Min. Coll 1, 1-10 (1919) Oppenheimer C, Stevenson D, Nature 342, 790-793 (1989) Symonds RB, Gerlach TM, Reed MH, J. Volc Geot Res 108, 303-341 (2001)