The sulfur flow fields of the Fossa di Vulcano

Abstract

Sulfur flow deposits at the Fossa di Vulcano fumarole field (Italy) are dominated by thermal erosion features. These are characteristic of sulfur flows at this location, where most flows are emplaced in a combusting mode such that all flow sulfur is melted and consumed during the emplacement event. Further, thermal erosion during emplacement results in pits and channels that mark the passage of the combusting flow. These thermal erosion pits and channels are typically littered with noncombusted silicate blocks, show overhanging rims and an absence of sulfur. If activity remains confined to a source fumarole basin, then sulfur lake activity will result. Combustion of such a feature leaves thermally eroded pits, typically a few tens of centimeters to a few meters wide and long, and a few tens of centimeters deep. However, the increase in sulfur volume during melting and erosion of pit walls mean that overflow and breaching is common. This leads to capture of new sulfur encrusted fumarole basins and flow extension. Flow extension away from the lake results in thermal erosion channels as much as 1.7 m wide, 0.6 m deep and 23.5 m long. Flow direction is dictated by slope, cinder ejection and sources of new sulfur, thus flows are capable of moving down, across and/or up slope if that is the dominant source of new sulfur. We estimate that sulfur flow activity has combusted 2,000-5,000 m 3 , or 4,000-10,000 tons, of sulfur at Vulcano. Only one noncombusted unit could be found during seven fumarole-fieldwide surveys during 1998-2003; this was 7.3 m long and 0.3 m wide, and had a viscosity of 0.1-40 Pa s. This viscosity is consistent with emplacement temperatures of 165-180C, which are lower than sulfur's combustion temperature. At Vulcano the commonality of thermal erosion features over noncombusted sulfur flow units indicates that combusting emplacement has been the main mode of flow emplacement at this volcano. The common occurrence of combustion is also evident from reference to the same phenomenon by DØodat de Dolomieu in 1783.

Sulfur Impurities: The Overlooked Process in Volcanic Hazard Assessment

“…S flows have been reported at several volcanoes where no crater lakes are present; among these is Vulcano, in Italy [66] (Figure 1), where the explosive Breccia di Commenda attests to an eruption of anomalously high amounts of S occurring ~1000-1200 CE [67].…”

Recognizing and tracking volcanic hazards related to non-magmatic unrest: a review

“…If a fumarolic system is heated to >116°C preexisting sulfur deposits in vugs and vents can be remobilized, manifested as a sulfur flow at the surface (Naranjo 1985;Oppenheimer 1992;Harris et al 2004). This feature is a clear sign of heating of a previously colder system, and thus often the onset of a state of non-magmatic unrest.…”

Physical and chemical characteristics of active sulfur flows observed at Lastarria volcano (northern Chile) in January 2019

“…Native sulfur is a common constituent of Earth's volcanoes and is found in the solid phase within fumarolic deposits in response to persistent fumarolic activity. Although native sulfur is highly abundant in fumarolic deposits, few volcanoes have evidence of molten sulfur, being a very "exotic" feature and, consuently, a target of interest for several studies (e.g., Wanatabe and Shimotomai, 1937;Oppenheimer and Stevenson, 1989;Greeley et al, 1990;Oppenheimer, 1992;Harris et al, 2004). Sulfur is the element with the largest number of allotropes (at least 30 different crystal structures in the solid phase), forming rings and unbranched chains of stable or metastable sulfur according to the temperature-pressure cooling conditions (Meyer, 1976;Steudel and Eckert, 2003).…”