Soil Gas Measurements

In order to better quantify volcanic gas fluxes, volcanologists have turned their attention also to diffuse degassing of CO2. Some volcanoes can release significant quantities of gas via diffuse flank emissions. At the workshop, six different research groups were using the Westsystems portable flux meter and conducted measurements at Masaya, Cerro Negro and Poas. In addition to investigating spatial variations in gas fluxes, experiments were conducted in the mornings and afternoons to check for temporal variations.

Group	Measurement time	F_CO2 range	m	s	CO₂ emission rate
		g m^-2 d^-1	g m^-2 d^-1	g m^-2 d^-1	t d^-1
1	AM	299-6905	1488	1401	1.34
1	PM	255-14,719	1618	2645	1.46
2	AM	362-7006	1767	1518	1.59
2	PM	341-11,158	1915	2226	1.72
3	AM	231-9292	1509	1633	1.36
3	PM	267-11,134	1803	2319	1.62
4	AM	218-11,924	2425	3216	2.18
5	AM	351-12,277	2188	2398	1.97

Thirty-six soil CO₂ flux (F_CO2) measurements were made by five groups at 5-m spacing along a grid located adjacent to Comalito cinder cone on the NE flanks of Masaya (March 27, 2003). Fluxes were measured by each group at each grid location within the same measurement footprint using the accumulation chamber method (e.g., Chiodini et al., 1998). Measurements were made along the grid by all groups between 11:00 and 13:00 (AM measurement time) and then repeated by Groups 1-3 between 14:00 and 16:00 (PM measurement time). Table above shows range, arithmetic mean (m), and standard deviation (s) of F_CO2 measurements made by each group. The total CO₂ emission rate was stimated by multiplying m by the measurement area (900 m²).