Institution: | 1. Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, Edifício C1, Campo Grande, 1749-016 Lisboa, Portugal;2. Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, Edifício C1, Campo Grande, 1749-016 Lisboa, Portugal
Departamento de Geologia, Faculdade de Ciências, Universidade de Lisboa, Edifício C6, Campo Grande, Lisboa, 1749-016 Portugal
School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ UK
Lamont-Doherty Earth Observatory, Columbia University, Comer Geochemistry Building, PO Box 3. 1000, Palisades, NY, 10964-8000 USA;4. Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig, 04103 Germany;5. Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, Edifício C1, Campo Grande, 1749-016 Lisboa, Portugal
Departamento de Geologia, Faculdade de Ciências, Universidade de Lisboa, Edifício C6, Campo Grande, Lisboa, 1749-016 Portugal;6. Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, Edifício C1, Campo Grande, 1749-016 Lisboa, Portugal
Instituto Superior de Engenharia de Lisboa, R. Conselheiro Emídio Navarro 1, Lisboa, 1959-007 Portugal |
Abstract: | In the Central Atlantic archipelagos – the Canaries, Cape Verde, Madeira and the Azores – tsunami hazard is often regarded as low, when compared with other extreme wave events such as hurricanes and storms. The geological record of many of these islands, however, suggests that tsunami hazard may be underestimated, notwithstanding being lower than in areas adjacent to subduction zones, such as the margins of the Pacific and Indian oceans. Moreover, tsunamis in oceanic islands are generally triggered by local large-scale volcanic flank collapses, for which little is known about their frequency, making it difficult to estimate the probability of a new occurrence. Part of the problem lies in the fact that tsunami deposits are usually difficult to date, and few islands in the world exhibit evidence for repeated tsunami inundation on a protracted timescale. This study reports on the presence of abundant tsunami deposits (conglomerates and sandstones) on Maio Island (Cape Verde) and discusses their stratigraphy, sedimentological characteristics, probable age and tsunamigenic source. Observations indicate that four distinct inundation events of variable magnitude took place during the Pleistocene. One of the tsunami deposits yielded a high-confidence U/Th age of 78·8 ± 0·9 ka, which overlaps within error with the 73 ± 7 ka age proposed for Fogo volcano's flank collapse, an event known to have had a significant tsunami impact on nearby Santiago Island. This shows that the Fogo tsunami also impacted Maio, resulting in runups in excess of 60 m above coeval sea-level at ca 120 km from the source. Two older deposits, possibly linked to recurrent flank collapses of the Tope de Coroa volcano in Santo Antão Island, yielded lower-confidence ages of 479 to 390 ka and 360 to 304 ka. A younger deposit (<78 ka) remains undated. In summary, the geological record of Maio exhibits well-preserved evidence of repeated tsunami inundation, reinforcing the notion that tsunami hazard is not so low at volcanic archipelagos featuring prominent and highly-active volcanoes such as in Cape Verde. |