En août 1883, l'éruption du Krakatau a provoqué des vagues de tsunami. Au centre et au Nord du détroit de la Sonde, peuples au moment de l’évènement de 1883 ont fourni de nombreux témoignages visuels des phénomènes volcaniques et des tsunamis. Les côtes sauvages et austères du Sud, notamment de la région de Ujung Kulon ont toujours été exemptes de populations. Il existe donc des lacunes dans les connaissances concernant le nombre et les caractéristiques des inondations de tsunamis sur ces côtes de Ujung Kulon. L’objectif de ce travail est d’explorer et de comprendre la façon dont les tsunamis générés par les différentes phases éruptives du Krakatau en1883 ont eu lieu à Ujung Kulon sur la base d’un déchiffrage aussi poussé que possible de l'enregistrement de phénomènes extrêmes dans des dépôts sédimentaire le long des littoraux sud du détroit de la Sonde. Pour atteindre cet objectif, trois méthodes d'analyse de texture et de composition sont appliquées, à savoir l'analyse de distribution granulométrique, l'identification des microfaunes et l’Anisotropie de la Susceptibilité Magnétique (ASM). Les résultats des analyses ont démontrés cependant que l'isthme en péninsule de Ujung Kulon a enregistré 4 (quatre) tsunamis liés aux éruptions et évidences que chaque vague a été enregistrée deux fois: i) par un flux direct provenant du détroit de la Sonde en ligne droite, ii) par une vague venant de l'océan Indien, retardée dans le temps après avoir été réfractée dans l’extrémité ouest de la péninsule de Ujung Kulon (près de l'île Panaitan). Cette preuve était unique et pourrait être liée au contexte géomorphologique exceptionnel de la péninsule de Ujung Kulon, y compris l'isthme et ses baies en forme de V, qui en font l'un des pièges les plus remarquables de dépôts de tsunami. / The giant tsunamis generated by the tremendous eruptions of Krakatau in 1883 were recorded along the coasts of Sunda Strait. Eyewitnesses testimony, tidal and pressure gauges recorded at Batavia (Jakarta), and tsunami signatures left by such event have been mostly used by researchers to evidencing the occurrence of the 1883-Krakatau tsunami around the Sunda Strait. Yet, there was still gap in knowledge when talking about the evidences of the 1883-Krakatau tsunami in the southern part of Sunda Strait and around Indian Ocean, due to the lack of eyewitness and a fact that some of the coasts is mostly noted as the remote areas. Laban Isthmus, one of the intriguing coastal landforms located 80 km to the south of Krakatau and connect Ujung Kulon Peninsula to Java Island, displayed the potential to record marine flooding events issuing from Sunda Strait and Indian Ocean. This study demonstrated however that the isthmus has recorded 4 (four) tsunami events related to the eruptions. Based on a new combination approach of sedimentary and micro-fossils analyses with the Anisotropy of Magnetic Susceptibility (AMS) technique, the result of the study evidenced that each wave was recorded twice: i) by a direct flow coming from the Sunda Strait in straight line, ii) by a wave coming from the Indian Ocean, delayed in time after having been refracted around the West-end of Ujung Kulon Peninsula (near Panaitan Island). Such evidence was unique and could be related to the exceptional geomorphological context of the Ujung Kulon Peninsula, including the isthmus and its V-shape bays, which made it one of the most remarkable traps of tsunami deposits.

Improving our understanding of magma plumbing and storage remains one of the majorchallenges for petrologists and volcanologists today. This is especially true for explosivevolcanoes, where constraints on magma plumbing are essential for predicting dynamicchanges in future activity and thus for hazard mitigation. This study aims to investigate themagma plumbing system at Anak Krakatau; the post-collapse cone situated on the rim of the1883 Krakatau caldera. Since 1927, Anak Krakatau has been highly active, growing at a rateof ~8 cm/week. The methods employed are a.) clinopyroxene-melt thermo-barometry (Putirkaet al., 2003; Putirka, 2008), b.) plagioclase-melt thermo-barometry (Putirka, 2005), c.)clinopyroxene composition barometry (Nimis & and Ulmer, 1998; Nimis, 1999; Putirka,2008) and d.) olivine-melt thermometry (Putirka et al., 2007). Previously, both seismic(Harjono et al., 1989) and petrological studies (Camus et al., 1987; Mandeville et al., 1996a;Gardner et al., in review, J. Petrol.) have addressed the magma plumbing beneath AnakKrakatau. Interestingly, petrological studies indicate shallow magma storage in the region of2-8 km, while the seismic evidence points towards a mid-crustal and a deep storage, at 9 and22 km respectively.This study shows that clinopyroxene presently crystallizes in a mid-crustal storage region(8-12 km), a previously identified depth level for magma storage, using seismic methods(Harjono et al., 1989). Plagioclases, in turn, form at shallower depths (4-6 km), in concertwith previous petrological studies (Camus et al., 1987; Mandeville et al., 1996a; Gardner etal., in review, J. Petrol.). Pre-1981 clinopyroxenes record deeper levels of storage (8-22 km),indicating that there may have been an overall shallowing of the plumbing system over thelast ~40 years. The magma storage regions detected coincide with major lithologicalboundaries in the crust, implying that magma ascent and storage at Anak Krakatau is probablycontrolled by crustal discontinuities and/or density contrasts. Therefore, this study shows thatpetrology has the sensitivity to detect magma bodies in the crust where seismic surveys faildue to limited resolution. Combined geophysical and petrological surveys offer an increasedpotential for the thorough characterization of magma plumbing at active volcanic complexes.