A blowhole is a geological feature formed in coastal cliffs, where a sea cave extends upwards to the surface, creating a hole through which air and water are expelled during high tides or stormy weather. Blowholes are indicators of coastal erosion processes and are significant in the study of marine geomorphology and coastal dynamics.
Reference: Stephenson, W. J., & Naylor, L. A. (2011). “Geological Controls on Benthic Habitats in Coastal Caves and Blowholes.” Geo-Marine Letters, 31(3), 181-191.