During the early hours of 1 November 1755, Lisbon was affected by a very powerful earthquake that violently shook the western and southern parts of Portugal. The earthquake, which occurred along the major fault line that separates Europe from North Africa, is estimated to have originated some approximately 200 km due south of Lisbon. The earthquake lasted nine minutes and consisted of three distinct jolts. It remains one of the most violent and longest seismic events on record, with an estimated intensity of between 8.5 and 9.0 on the Richter scale.
The effects of the Lisbon earthquake were felt over a vast area, stretching from North Africa to Sweden. Some contemporary references suggest the earthquake’s impact on Ireland:
Upon Saturday the 1st of November at thirty-six minutes after nine o’clock, a sensible shock of an earthquake was felt at Cork; it continued for about a minute.
The large tsunami that followed consisted of multiple waves. Some forty minutes after the earthquake, these waves engulfed Lisbon. Wave heights varied between 6 and 30 metres along Portuguese and Spanish coasts. The tsunami-train reached Brazil to the west, North Africa to the south and Britain and Ireland to the north. A letter from 1755 describes the arrival of the tsunami in Kinsale:
…a large body of water suddenly poured into the harbour … the successive risings and fallings of the water continued about 10 minutes… By different accounts received here the water was affected in the same manner along the coast, to the westwards of this harbour.
The highest tsunami wave may have reached 13 feet or just under 4 metres.
Effects of the Earthquake, Firestorm and Tsunami
The effects of the earthquake, and resulting firestorm and tsunami in Lisbon, were devastating, destroying much of the city, and caused further destruction along the Iberian and North African coastline. It is impossible to know how many people died as a result of his event but a figure of 50,000 would not be unrealistic and could have been higher. It is also possible that there were fatalities in West Cork.
After every major earthquake, aftershocks occur. Over 250 tremors were recorded in Lisbon in the six months after the 1755 event, while further earthquakes also occurred for years after. As many as five earthquakes were felt in Ireland between the end of 1755 and the beginning of 1762. On March 30th, 1761, an earthquake was felt in Cork city. It lasted a minute and remarkably was followed by a second tsunami. In Kinsale, a water surge of two feet or 0.6 metres occurred at low tide, and suddenly withdrew after four minutes.
Impact of the 1755 Tsunami on West Cork
Although the contemporary documentary record is very slight, the impact of the 1755 tsunami on the coast of West Cork is remembered some ten generations later. A series of interviews with local people (supported by the Heritage Council) was completed by Anthony Beese, one of the authors of the present blog.
The study aimed to match the contours of the oral tradition to the record of the physical landscape. Since much of the folklore was concerned with the sand dunes at Barley Cove, Rosscarbery and Long Strand, it was decided to undertake a geomorphological assessment of the ‘soft coast’ (coast made up of sand and other loose sediment and bedrock). The purpose of this part of the investigation was to estimate the coast’s vulnerability to the 1755 event. In a few cases, the record was surprisingly full and detailed. For example, it was possible to estimate the likely degree of local ‘run-up’ (a measure of the maximum elevation reached by the surge of water as it pushes inshore) of the tsunami at Rosscarbery and at some other exposed locations.
Many of the tales of dramatic sand movements in the inlets of West Cork reflect the kinds of geomorphological changes that occurred on sand-barrier coasts after the Indian Ocean tsunami of 2004. It appears that the wave-train penetrated a considerable distance along the Bandon River estuary, reworking sediment and causing damage to boats and quays. Many of these stories are supported by the wider oral tradition, though it is also clear that some of the folklore was exaggerated. For example, at Cape Clear, the story was told by several islanders of the division of the main island into two parts by an enormous ‘tidal wave’. But later, another version of events told of a lesser inflow of water that breached a low-lying tract on the island’s western side. This last tale came from the ‘old people’ and seemed more likely to be true.
Dr Kieran Hickey (University College Cork) and Dr Anthony Beese (Carraigex GeoServices)
Trelispean Bay, West Cork
Professor Robert Devoy, a coastal scientist at University College Cork, has conducted research into the record of 1755 tusnami at Trelispean Bay, West Cork. As he explains in the video below, the tsunami wave probably exited this area from Trelispean Bay and on into Tregumna Bay.