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Between September 19 and December 13, 2021 a strombolian volcanic eruption took place on the island of La Palma. The main edifice was appeared at an altitude of around 900 masl, reaching 1122 masl at the end of the process. The Roque de los Muchachos Observatory (ORM) is an outstanding international astronomical site, hosting some of the most important astrophysical facilities of the world. The Observatory is located 16 km away from the eruptive cone, in the summit of the island, at an altitude ranging between 2200 and 2400 masl. The atmospheric conditions at the Canary Islands conform an almost permanent thermal inversion layer below the level of the observatory that modulated the arrival of the volcanic plume. In this work we are going to briefly review the influence of different parameters associated to the eruption in the ORM routine operation. We will evaluate the impact of the seismic activity, volcanic ash falling, presence of SO2 and airborne particulate matter. The number of days with high remarkable values recorded of these parameters were few. Nevertheless, the actual impact on the different telescopes was heterogeneous, depending on the different risk evaluations, and recovery/response times. An impact report with a compilation of measurements and forecasts was released twice a day during the whole process to help facilities in the daily operational decision making. As a final conclusion, no damages were suffered in any of the installations. Although an important downtime was reported, astronomical observations continued in different degree during the whole episode.

Since proposed by Bevis et al. in 1992, GNSS Meteorology has become a very competitive field, mainly because it provides a relatively cheap, extensive network of stations, with global and 365d/24h coverage. Therefore, the method has been widely validated by comparison with other reference techniques. A majority of the comparisons show both dry or wet bias for the PWV obtained from GNSS, depending on the particular station, as a consequence of such an heterogeneous network working on a vast set of atmospheric scenarios. Thus, most of the effort has been focused on getting the best possible global information, guarantying homogeneity. Instead, the goal of a PWV monitor for Astronomy is not homogeneity, but getting the most out of a particular station. In this work we aimed a high precision and high accuracy real-time monitor supporting IR and μW astronomical observations. We have reviewed the technique and identified the external factors impacting in the final error, including local barometric pressure and temperature measurements, weighted mean temperature based on local vertical profiles, and an independent calibration through a detailed comparison with high vertical resolution radiosondes. We discuss the final error and accuracy achieved, the lower detection limit of the technique, and possible new improvements.

In 2010, it was published an analysis of the impact of geological activity on the main astronomical observatories worldwide (Eff-Darwich et al., 2010), among them, Roque de los Muchachos observatory (ORM), in the island of La Palma, Canary Islands (Spain). In this work, we compare the results on geological risk at ORM that were obtained in 2010 with the actual impact of Cumbre Vieja eruption. In this sense, we studied the effects of seismicity, ash fall, landslides and ground deformation at ORM. In general, we found a good agreement between the expected and actual impact of volcanic activity at the observatory; however, large differences were found in the distribution of ash fall, likely due to the improper characterization of the atmospheric inversion layer in the model of the dispersion of the volcanic plume. Eff-Darwich, A., García-Lorenzo, B., Rodríguez-Losada, J., de la Nuez, J., Hernández-Gutiérrez, L., Romero, C., Monthly Notices of the Royal Astronomical Society, Volume 407, Issue 3, September 2010, Pages 1361–1375, https://doi.org/10.1111/j.1365-2966.2010.16925.x