Researchers of the Instituto Dom Luiz (IDL) identified a buried landslide that accounted for the collapse of half of the Tagus river ebb-tidal delta front possibly in the early Holocene. In this work, recently published in the journal Marine Geology, the stratigraphy of the Tagus river ebb-tidal delta off Lisbon (Portugal) was investigated using high resolution multichannel seismic reflection profiles with the purpose of searching for sedimentary or erosive features associated with landslides. Also, the implications of landslide driven tsunamis and impact on submarine cables caused by submarine landslides in the region of Lisbon and the southwestern Iberian margin were discussed. Based on these works, a buried structure of a landslide of about 11 km long, 4 km wide and a maximum thickness of 20 m was identified, which caused the collapse of about half of the Tagus delta, approximately 8,000 years ago. The mechanisms that would have triggered this landslide have not been yet determined. However, the correlative age with turbiditic deposits identified in the Tagus Abyssal Plain may indicate a relationship between this landslide and seismic activity. These studies are particularly relevant for assessing the susceptibility of coastal areas and offshore infrastructures to hazards related to large-scale landslides.

The work was led by Pedro Terrinha (IPMA-IDL) in collaboration with other IDL researchers, Rachid Omira, Maria Ana Baptista, Miguel Miranda, Vitor Magalhães and Cristina Roque, as well as researchers from other centers, namely the Instituto Português do Mar e da Atmosfera (IPMA), the Universidade de Évora, the Instituto Superior de Engenharia de Lisboa (ISEL) and the company Geosurveys – Consultorem em Geofísica.

The work continues with the investigation of the origin of the gas in the sediments of the submarine delta in the project TAGUSGAS (Univ. Évora, IPMA) and modeling of tsunamis generated by landslides in the MAGICLAND project (IDL, IPMA, Univ. Coimbra), both financed by FCT.

KeywordsTagus River – NE Atlantic; Ebb-tidal delta; Seismic stratigraphy; Submarine landslide; Tsunami hazard

You can access the publication here.