In the Local Natural Monument of Canto Marinho, granite blocks are observed, which constitute an excellent example of one of the mechanisms of regional magmatic installation, namely the pervasive (diffuse) magma migration. These granite blocks, some weighing more than 10 tons, were generated by the migration of giant magma droplets that migrated from the main magmatic chamber that gave rise to Montedor (LNM Alcantilado de Montedor), and between fractures they consolidated here, about 700m and that came to be interpreted as a deposit (tsunamite) generated by the oldest tsunami that is recorded in Portuguese seismic catalogs, from 66 BC.

References:

Carvalhido, Ricardo (2018). Livro de Pedra, Monumentos Naturais Locais de Viana do Castelo – Catálogo. Câmara Municipal de Viana do Castelo, 2ª edição.