Impact of the tsunami caused by the Hunga Tonga-Hunga Ha'apai eruption in Costa Rica on 15 January 2022.

Hunga Tonga-Hunga Ha'apai had a large eruption (VEI 5-6) on 15 January 2022, which caused a tsunami recorded in all ocean basins. Costa Rica has made many advances in tsunami preparation over the past 9 years since the creation of SINAMOT (Sistema Nacional de Monitoreo de Tsunamis, National Tsunami Monitoring System), both on watch and warning protocols and on community preparedness. For the Hunga Tonga-Hunga Ha'apai event, the government declared a low-threat warning, suspending all in-water activities, even though the country did not receive any official warning from PTWC (Pacific Tsunami Warning Center) due to the lack of procedures for tsunamis generated by volcanoes. The tsunami was observed at 24 locations on both the Pacific and Caribbean coasts of Costa Rica, becoming the second most recorded tsunami in the country, after the 1991 Limon tsunami along the Caribbean coast. At 22 of those locations along the continental Pacific coast, observations were made by eyewitnesses, including one collocated with the sea level station at Quepos, which registered the tsunami. At Cocos Island (~ 500 km southwest of the continental Costa Rica, in the Pacific Ocean), several eyewitnesses reported the tsunami at two locations, and it was recorded at the sea level station. The tsunami was also recorded at the sea level station on the Caribbean coast. The tsunami effects reported were a combination of sea level fluctuations, strong currents, and coastal erosion, proving that the response actions were adequate for the size of the tsunami. Tsunami preparedness and the largest waves arriving during a dry season Saturday afternoon allowed the large number of eyewitness reports. This event then increased tsunami awareness in the country and tested protocols and procedures. Still, many people along the coast were not informed of the tsunami during the alert due to their remote location, the short notice of the warning, and a lack of procedures for some communities. There is thus still much work to do, particularly about warning dissemination, a direction in which communities should take an active role. Supplementary Information: The online version contains supplementary material available at 10.1007/s00445-023-01648-x.