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.

Le secteur de Kajhu Perumnas situé au nord-est de Banda Aceh à l’extrémité nord de Sumatra correspond à une vaste plaine côtière surbaissée où la dizaine de vagues constituant le train d’ondes du tsunami du 26 décembre 2004 a totalement arraché les arbres, gommé les dunes du bord de mer, arasé le bâti et pénétré à plus de trois kilomètres à l’intérieur des terres. Les dépôts sédimentaires, étudiés à la lumière des témoignages recueillis sur le comportement des vagues, présentent une différenciation nette et progressive de la signature du tsunami à mesure qu’on s’éloigne du rivage. Les dépôts grossiers et indifférenciés en domaine proximal présentent un nombre croissant de séquences à grano-classement positif à mesure qu’on passe en domaine intermédiaire puis distal, au sein duquel sept séquences peuvent être observées. Une fois les espaces côtiers libérés des eaux, les sédiments de surface ont subi une déflation éolienne active qui a contribué à former de petits champs de dunes qui s’engraissent rapidement. Au cours de l’année qui a suivi le tsunami, 1 100 m³ de sable par hectare ont ainsi été accumulés dans le secteur étudié. Cette dynamique s’est ralentie, puis a cessé entre six mois et un an après l’événement à cause de la reconquête végétale sur les zones de déflation. Cette reconquête est commandée par la désalinisation du sable sous l’effet de la pluie. L’association végétale de reconquête actuelle n’est pas différente des successions pionnières habituelles sur les espaces sableux de cette région. Le retour d’importants volumes de sédiments vers la mer lors des épisodes pluvieux contribue à alimenter la dérive littorale qui favorise l’engraissement des plages et le déplacement du trait de côte vers la mer, de 150 à 500 m en un an entre juin 2005 et août 2006.

The Unzen Volcano, located at the centre of the Shimabara Peninsula is a stratovolcano that has left scars both in the landscapes and the lives of local inhabitants. After almost two centuries of slumber, the Unzen erupted during the period 1990-1995, producing numerous dome-collapses pyroclastic flows that engulfed a large part of the structure. Using a dataset retrieved by structure-from-motion from historical imagery, the present contribution provides an insight on the landscape trajectory of the volcano between the period 1947 and 2013, using the lenses of geomorphology and biogeography. The results have shown that the volcano has been evolving in two different manners since the eruption. The summit area of the volcano still holds a large amount of material (pyroclasts of 50 m depth have been measured from the 1998 imagery). This area has seen a return of the vegetation, which contrasts with the foot of the volcano, trapped in a concrete coffin, limiting the return of vegetation and living the wounds of the eruption open. Finally, at the exit of the Mizunashigawa, the impacts of the eruption have spread to the shore, with a linear expansion over the sea of almost 500 m. In Conclusion, this contribution shows that it isn’t much the volcanic eruption that modified the landscape over long periods of time, but the human infrastructure that stops some part of the landscape to evolve.

Numerous progress has been made in the field of applied photogrammetry in the last decade, including the usage of close-range photogrammetry as a mean of conservation and record of outcrops. In the present contribution, we use the SfM-MVS method combined with a wavelet decomposition analysis of the surface, in order to relate it to morphological and surface roughness data. The results demonstrated that wavelet decomposition and RMS could provide a rapid insight on the location of coarser materials and individual outliers, while arithmetic surface roughness were more useful to detect units or layers that are similar on the outcrop. The method also emphasizes the fact that the automation of the process does not allows clear distinction between any artefact crack or surface change and that human supervision is still essential despite the original goal of automating the outcrop surface analysis.

In the framework of prevention, it is necessary to understand the dynamics of a tsunami. In order to develop hydrodynamic model, we used geo-statistical tools to reconstruct the tsunami of December, 24th, 2004 at Banda Aceh (Indonesia). On a area of 20 km², about 1000 angles were measured, based on impact of the wave. To simplify the modelling, we assume unicity of the wave. Classical spatial statistics cannot be used in this problem since (i) kriging is not invariant by rotation; (ii) the arithmetic mean cannot be used for circular data. We first review common adaptations of kriging to circular data. Drawbacks of these methods are illustrated on our example. Finally we extend circular data theory to spatial statistics.