Remote determination of SiF₄ in volcanic plumes: A new tool for volcano monitoring

Abstract

SiF4 is probably a common trace component of fumarole gases on volcanoes, arising from interactions between magmatic HF and wall rocks. It is not distinguished from HF in conventional analyses. A strong absorption band at 1032 cm−1 makes SiF4 well suited to remote open‐path FTIR spectroscopic techniques. We report the first measurements of SiF4 in volcanic gases at Etna and Vulcano (Sicily). SiF4 concentrations were low at Etna, but higher at Vulcano, where the SO2: SiF4 ratio was consistently around 1.7×10−2: 1. Thermodynamic considerations show that the HF : SiF4 ratio increases sharply with increasing temperature. Thus, remote measurements of SiF4 may offer a qualitative way of constraining fumarole temperatures. We use our FTIR measurements of HCl: SiF4 in combination with conventional measurements of HCl: HF to infer an HF :SiF4 ratio for Vulcano of ∼10:1, consistent with gas temperatures in the range 200–450°C.

High SiF4/HF ratio detected in Satsuma-Iwojima volcano’s plume by remote FT-IR observation

“…Figure 4 shows a typical observed absorbance spectrum between 950 and 1250 cm −1 with the MCT detector. It may be compared with figure 1 of Francis et al (1996), which was obtained at Vulcano, Italy. The observed absorbance spectrum clearly shows absorption features of SO 2 (ν 1 band) and SiF 4 .…”

“…The average SiF 4 /HF molar ratio in the plume of Satsuma-Iwojima is obtained as 0.57 using the OHO results with the uncertainty of about Francis et al (1996); Popocatépetl, Love et al (1998)). …”

“…So far seven species, SO 2 , HCl, SiF 4 , CO, COS, HF and CO 2 , in volcanic gases were measured by this technique (Mori et al, Copy right c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. , 1995Mori and Notsu, 1997;Francis et al, 1996Francis et al, , 1998Love et al, 1998;Oppenheimer et al, 1998). The techniques for field measurements are well documented in Oppenheimer et al (1998).…”

Airborne volcanic plume measurements using a FTIR spectrometer, Kilauea Volcano, Hawaii

“…The prototype closed-path FrlR system described here, built by MIDAC Corporation to USGS specifications, has step-selectable resolution from 32 cm -j to 0.5 cm -1 and contains a plane mirror Michelson interferometer consisting of a beamsplitter, fixed mirror, and moving mirror (McGee, 1996). The broadband light source is a 1660 K silicon carbide air-cooled globar.…”

Remote CO, COS, CO2, SO2, HCl detection and temperature estimation of volcanic gas

“…This method has been successfully applied for measurements of SO• and HC1 at Unzen (Japan), Vulcano and Etna (Italy) volcanoes [Mori et al, 1993;Francis et al, 1995;Mori et al, 1995], minor gas components such as SiF4 at Vulcano and Etna [Francis et al, 1996b], and CO at KujuIwoyaxna volcano, Japan, which erupted in October 1995 [Ono et al, 1997]. CO and COS emitted by Galeras volcano, Colombia, has been measured also by using nondispersive infrared remote sensing technique [Stix et al, 1996].…”