Impact at the astronomical Observatory of Roque de los Muchachos from the Cumbre Vieja 2021 volcanic eruption at La Palma.

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.