[S-VC28] International Volcanology

[SVC28-P09] Auto-sampling of volcanic fluids: testcases at Canary Islands, Spain

*TOSHIYA MORI¹, Cecilia Amonte², Pedro A. Hernandez^2,3, Nemesio M. Perez^2,3 (1.The University of Tokyo, 2.Instituto Volcanologico de Canarias (INVOLCAN), 3.Instituto Tecnologico y de Energias Renovables (ITER))

Keywords:volcanic fluids, automated sampling, Canary Islands, carbon dioxide, groundwater

Geochemical monitoring of volcanic fluids has shown high potential for elucidating volcanic activities. Recent continuous measurements of diffuse CO₂ emissions by accumulation chamber method and of volcanic plume composition by MultGAS have proved the importance of high frequency information in geochemical monitoring. Yet, majority of geochemical monitoring especially to obtain precise and detailed information are still relying on sampling and laboratory analyses by researchers. Considering a manpower of a research group or safety concerns of the researchers, conducting frequent sampling of hours to several days intervals at volcanoes is unrealistic. Thus, we may overlook some important signals or turning point of activities occurring within a few days or a week time scale. To overcome this problem, Ono et al. (2020) developed an automated sampling tool for hot spring waters using a CNC (computer numerical control) machine controlled by a programming language G-code, and named the sampler as GOFAT (G-code Operated Field Auto-sampling Tool). The GOFAT detected quick change (shorter than a few days) of dissolved components concentrations in the hot spring water, which had not been recognized by periodic sampling of several week interval.
By improving the GOFAT of Ono et al. (2020), we built new types of GOFATs for water and gas samples based on laser engravers. The GOFAT for water sampling (GOFAT-W) is basically the same with Ono et al. (2020). Since gas samples should be collected into a vial with septum, the GOFAT for gas sampling (GOFAT-G) is equipped with a linear actuator connected to two syringe-needles welded together. This needle system connected to a pump via plastic tube is inserted into the vial with the linear movement of the actuator. The sample gas is then pumped into the vial for collection. The GOFAT-G automatically collect samples into 120 vials which are arranged horizontally and vertically at fixed time intervals.
We have been testing the two types of GOFAT at Canary Islands, Spain since Oct. 2022. The water samplings were carried out at two groundwater galleries (San Fernando and Fuente del Valle galleries in Tenerife) where solvent compositional changes were observed related to seismic activities increase at Teide volcano in Oct. 2016 (Amonte et al., 2021). Two GOFAT-W have been operated with high sampling rate of 3 samples/day or 1 sample/day.
The GOFAT-G has been operated at Puerto Naos village, La Palma Island. Although the village was not directly damaged by the lava flow of the 2021 eruption of the island, the residents were forced to evacuate the village due to significant volcanic CO₂ emission started in Nov. 2021. The GOFAT-G is placed in a closed garage in Puerto Naos and has been sampling air whose CO₂ concentration frequently exceed 4%. Here the auto sampling has been made since October 2022 with frequency of 4 times a day ( the sampling stopped in about two weeks due to the mechanical trouble but re-installed in Feb. 2023 with the frequency of twice a day). The auto samplings have provided important information especially at Puerto Naos to understand the nature of the high CO₂ emission at the village related to volcanic phenomena. In our presentation we will show the results of auto-sampling and discuss the importance of frequent sampling in geochemical monitoring.