Evidence of Unknown Paleo-Tsunami Events along the Alas Strait, West Sumbawa, Indonesia

Bachtiar W Mutaqin (1) , Franck Lavigne (2) , Patrick Wassmer (2) , Martine Trautmann (3) , Puncak Joyontono (4) , Christopher Gomez , Bagus Septiangga , Jean-Christophe Komorowski (5) , Junun Sartohadi (6) , Danang Sri Hadmoko (7)

1 UGM - Faculty of Geography, Universitas Gadjah Mada
2 LGP - Laboratoire de géographie physique : Environnements Quaternaires et Actuels
3 EOST - Ecole et Observatoire des Sciences de la Terre
4 UGM - Environmental Geography, Universitas Gadjah Mada, Indonesia
5 IPGP (UMR_7154) - Institut de Physique du Globe de Paris
6 OSUG - Observatoire des Sciences de l'Univers de Grenoble
7 UGM - Faculty of Geography, Universitas Gadjah Mada

Indonesia is exposed to earthquakes, volcanic activities, and associated tsunamis. This is particularly the case for Lombok and Sumbawa Islands in West Nusa Tenggara, where evidence of tsunamis is frequently observed in its coastal sedimentary record. If the 1815 CE Tambora eruption on Sumbawa Island generated a tsunami with well-identified traces on the surrounding islands, little is known about the consequences of the 1257 CE tremendous eruption of Samalas on the neighboring islands, and especially about the possible tsunamis generated in reason of a paucity of research on coastal sedimentary records in this area. However, on Lombok Island, the eruption of the Samalas volcano produced significant volumes of pyroclastic flows that entered the sea in the North and East of the island. These phenomena must have produced a tsunami that left their traces, especially on Sumbawa Island, whose western coastline is only 14 km away from Lombok’s eastern shore. Therefore, the main goal of this study is to investigate, find evidence, and determine the age of marine-origin sediments along the shore of the Alas Strait, Indonesia. We collected and analyzed samples of coral and seashells from marine deposits identified along the west coast of Sumbawa, i.e., in Belang Island and abandoned fishponds in Kiantar Village, in order to identify the sources and the occurrence period of these deposits events. Based on the radiocarbon dating of coral and seashell samples, we concluded that none of the identified marine deposits along the western coast of Sumbawa could be related chronologically to the 1257 CE eruption of Samalas. However, possible tsunami deposits located in Belang Island and abandoned fishponds in Kiantar Village yielded 4th century CE, 9th century CE, and 17th century CE. We also conclude that past large earthquakes triggered these tsunamis since no known volcanic eruption occurred near the Alas Strait at that time that may have triggered a tsunami.

Mots clés: paleo-tsunami; grain size; radiocarbon dating; wave direction; Lombok; Sumbawa; Indonesia; paleo-tsunami

Domaines: Sciences de l'environnement

Bachtiar W Mutaqin, Franck Lavigne, Patrick Wassmer, Martine Trautmann, Puncak Joyontono, et al.. Evidence of Unknown Paleo-Tsunami Events along the Alas Strait, West Sumbawa, Indonesia. Geosciences, 2021, 11 (2), pp.46. ⟨10.3390/geosciences11020046⟩. ⟨hal-03958458⟩