Volcanic emission rates of SO2 at Mount Erebus have been measured during the austral summer from 1983 to 2001 by correlation spectrometer (COSPEC V). Below are some of the results from these measurements.
Table below reproduced from Kyle, P.R., Sybeldon, L.M., McIntosh, W.C., Meeker, K., and Symonds, R., 1994, Sulfur dioxide emission rates from Mount Erebus, Antarctica, in Kyle, P.R., ed., Volcanological and Environmental Studies of Mount Erebus, Antarctica, Volume 66: Washington, D.C., American Geoophysical Union, p. 69-82.
Mt Erebus is the most active volcano in Antarctica and is a significant source of aerosols and gases to the Antarctic atmosphere. It is a unique volcano to study gas and aerosol emissions because, relative to other volcanoes, Mt Erebus is isolated from man-made contaminats in the atmosphere and because it has a very unusual alkalic composition. Mt Erebus is currently the only known active volcano with lava of anorthoclase phonolite and one of the few volcanoes known to have a convecting lava lake. Because of the alkalic nature of the magma, experimental studies would predict that the gases should be CO2-rich. In addition, studies of dissolved CO2 in melt inclusions found in olivine crystals have shown that the parental basanite, which evolves by fractional crystallization from the phonolite, have some of the highest CO2 concentrations to date (Eschenbacher et al., 1998). A further indication of high levels of CO2 in the gas emissions in inferred from the extremely high carbon monoxide emissions measured in 1996. A CO/SO2 ratio of 3 was determined in the plume using an open field fourier transform infrared (FTIR) spectometer. Annual measurements of SO2 emissions made during the 1990's by correlation spectrometer (COSPEC) have shown SO2 fluxes of 50-70 mega-grams per day (Mg/day). This SO2 flux then implies that the CO emission rate is over 150 Mg/day. Clearly the high CO emission rates are a function of high CO2 concentrations and low oxygen fugacity. It was therefore of much interest to make direct measurements of the CO2 emissions from Mt Erebus.
A direct airborne CO2 measurement was made in the plume of Mt Erebus during the 1997-1998 field season using a LICOR 6262, infrared CO2 analyzer. The intake hose for the analyzer was mounted to the nose antenna of an A-Star helicopter. The analyzer was flown in a grid pattern through a cross-section of the plume, perpendicular to the wind direction (Figure 1, Figure 2). The aircraft position was monitored using a differential GPS system. A CO2 flux of 1,850 Mg/day was determined by multiplying the cross-sectional concentration by the wind speed. Soil gas emissions of CO2 are also high at Mt Erebus and elevated CO2 levels have been observed in fumarolic ice towers. The CO2 concentration inside one ice tower was 15,000 ppm, this compares to the ambient atmospheric concentration of ~350 ppm. Soil CO2 flux values ranged from 0 to 4,400 g/m2/day and indicate that significant CO2 degassing is occuring as soil gas in the summit area. Carbon isotope analyses of CO2 from soil gases show a delta13 range of 3.4 to 3.8 per mil, indicating that degassing from the flanks is magmatic and not of biogenic origin.
Carbon dioxide emissions from volcanoes are of interest due to the potential significance of global volcanic contributions of this greenhouse gas. CO2 flux measurements from active volcanoes are also useful in hazard prediction and may also give insight to the eruptive mechanisms within a particular volcanic system (Gerlach et al., 1997). Mt Erebus, Antarctica, being the southernmost active volcano, is of particular interest due to its potential impact on the pristine Antarctic environment. Mt Erebus is currently the only known active volcano with lava of anorthoclase phonolite and one of the few known to have a convecting lava lake. Because of the alkaline nature of the magma, experimental studies would predict that the gases should be CO2-rich. Therefore, it was of much interest to make direct measurements of CO2 emissions from Mt Erebus.
In December 1997, the CO2 flux of Mt Erebus was calculated using direct airborne measurements. A LI-COR CO2 analyzer was coupled with a Trimble differential GPS system and flown on board a helicopter through the volcano plume. CO2 measurements were made at one-second intervals along the flight trajectory as recorded by differential GPS. Prior to this work, this technique has only been employed at two other volcanoes; at Oldoinyo Lengai, Tanzania (Kopenick et al., 1996) and Popocatepetl, Mexico (Gerlach et al., 1997). The assistance from UNAVCO provided instrumentation and technical support for the acquisition of differential GPS data.
Open-path fourier transform infrared (FTIR) spectroscopy can remotely provide relative concentrations of numerous gas species. In December, 1995, an FTIR system which was employed on Mt Erebus was able to detect carbon monoxide concentrations. The CO/SO2 results from the FTIR scans are multiplied by the SO2 flux rate determined by the correlation spectrometer (COSPEC) which is also a remote sensor.
Results exhibit good precision when scans are repeated the same day. Extrapolating the average CO/SO2 ratio (2.96) with the SO2 flux (49 Mg/day), a CO flux of 150 Mg/day results.
Soil Gas and Fumaroles
Soil gas flux was measured by the accumulation chamber method using the same analyzer used to make the direct airborne measurments. For this method, a box is placed open-side-down on the soil surface and the rate of accumultaion of CO2 inside the box is measured and calculated per unit area. Flux rates were approximatley zero on permafrost areas while warm ground exhibit varying fluxes. The area known as Tramways, which is a Site of Special Scientific Interest, host a unique biota supported by the warm gaseous emissions. Soil flux as high as 4,400 g/m2/day were recorded. Actively degassing fumaroles that were measured all contained CO2 conctrations above ambient (~350 ppm). The highest concentration observed in an active fumarole was 15,000 ppm. This concetration was above the range of the portable analyzer and samples were transported to McMurdo Station for analyses. Gas samples were also collected from warm ground and fumaroles for isotopic carbon analyses. Delta13 values ranging from 3.4 to 3.8 per mil, confirmed that the CO2 is of magmatic origin.
The total flux of CO2 from Mt Erebus is 1,850 Mg/d. Table 2 lists the volcanic output in ranking by the available CO2 flux data for subaerial volcanoes worldwide. This ranks Mt Erebus within the top ten known CO2 producing volcanoes in the world. Kopenick et al., 1996, report the accuracy of this direct airborne technique of measuring volcanic CO2 flux to be within 10% when evaluated at a coal-burning power plant.
Although numerous soil gas and fumarole measurements were made on Mt Erebus, a significant portion of the edifice was not accessed so a total flux from the flanks has yet to be determined. Due to high concentrations in some of the fumaroles and large flux rates from areas of warm ground, this source of degassing may prove to be significant. Table 2 shows that contributions from soil degassing are variable and can be as high as 50%.
The CO2/CO data in Table 2 are derived from laboratory measurements of fumarole samples, with the exception of Mt Erebus which is derived from known flux rates. It appears evident that hot spot volcanism exhibits a lower ratio than do convergent plate volcanoes and is an indicator of oxygen fugacity.
Allard, P. (1998). Magma-derived CO2 budget of Mount Etna. EOS Transactions/Supplement, vol 79, no 10, p F927.