December 18, 1926 Tsunami: Portugal

The waters of the Tagus River rose considerably and soon the water was covered with thousands of fish. (reference #41)

Reference #2076 states the Tagus [river] in Lisbon stirred, and the same happened with the sea in front of Cascais, with the water reaching the railway line.

Reference #4649:

Event reliability 4 (definite tsunami).

The Lisbon newspaper Diario de Noticias (1926) reports “[. . . ] Great agitation in the Tagus, it was felt in most boats that were leaned to the wall [. . . ]. A curious report by several persons, that were using the Tagus ferries, is that the fishes were alarmed with the agitation of the sea and came to the surface in groups [. . . ]. Groups of brave individuals approached the “Column Quay” to watch what was going on in the river [. . . ]”. This event shares some similarity with the 1531 Tagus event. Berninghausen (1964) reports the 1926 tsunami quoting the Seismological Dispatches of the University of Georgetwon. Cascais tide gauge station shows no clear tsunami waveform; the Seismological Dispatches of Georgetown university for this year report: ”[. . . ] Lisbon, Portugal, Dec. 18 A violent earthquake lasting three seconds, today alarmed all Lisbon [. . . ]” and for the next day: ”[. . . ] Lisbon, Portugal Dec. 19 – Lisbon has experienced a severe earthquake. The first shock Saturday lasted ten seconds. It was accompanied by subterraneous noise; the waters of the Tagus river rose considerably and soon the surface was covered with thousands of fish [. . . ] (Tendorf, 1926).

In the case of the 1926 Tagus event, and taking into consideration the low presumed magnitude of the associated earthquake, and the lack of coherent tsunami signal in Cascais tide gauge, out of the Lisbon bar, we consider as the most probable cause an earthquake marine slide in the Estuary.