See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/235225380 Tsunami hazard related to a flank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia Article in Geological Society London Special Publications · January 2012 DOI: 10.1144/SP361.7 CITATIONS READS 11 1,794 4 authors, including: Thomas Giachetti Raphaël Paris University of Oregon Université Clermont Auvergne 29 PUBLICATIONS 406 CITATIONS 161 PUBLICATIONS 2,165 CITATIONS SEE PROFILE SEE PROFILE Karim Kelfoun Université Clermont Auvergne 73 PUBLICATIONS 1,094 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Geomorphology in Iceland View project Geomorphologic Crisis in Coastal Environments View project All content following this page was uploaded by Thomas Giachetti on 02 June 2014. The user has requested enhancement of the downloaded file. Downloaded from http://sp.lyellcollection.org/ by guest on March 12, 2012 Geological Society, London, Special Publications Tsunami hazard related to a flank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia T. Giachetti, R. Paris, K. Kelfoun and B. Ontowirjo Geological Society, London, Special Publications 2012, v.361; p79-90. doi: 10.1144/SP361.7 Email alerting click here to receive free e-mail alerts when service new articles cite this article Permission click here to seek permission to re-use all or request part of this article Subscribe click here to subscribe to Geological Society, London, Special Publications or the Lyell Collection Notes © The Geological Society of London 2012 Downloaded from http://sp.lyellcollection.org/ by guest on March 12, 2012 Tsunami hazard related to a flank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia T. GIACHETTI1,3*, R. PARIS2,4,6, K. KELFOUN2,4,6 & B. ONTOWIRJO5 1Clermont Universite´, Universite´ Blaise Pascal, Geolab, BP 10448, F-63000 Clermont-Ferrand, France 2Clermont Universite´, Universite´ Blaise Pascal, Laboratoire Magmas et Volcans, BP 10448, F-63000 Clermont-Ferrand, France 3CNRS, UMR 6042, Geolab, F-63057 Clermont-Ferrand, France 4CNRS, UMR 6524, LMV, F-63038 Clermont-Ferrand, France 5Coastal Dynamics Research Center, BPDP-BPPT, 11th Floor, Building 2, BPPT, Jl, M. H. Thamrin no 8, Jakarta 10340, Indonesia 6IRD, R 163, LMV, F-63038 Clermont-Ferrand, France *Corresponding author (e-mail: [email protected]) Abstract: Numerical modelling of a rapid, partial destabilization of Anak Krakatau Volcano (Indonesia) was performed in order to investigate the tsunami triggered by this event. Anak Krakatau, which is largely built on the steep NE wall of the 1883 Krakatau eruption caldera, is active on its SW side (towards the 1883 caldera), which makes the edifice quite unstable. A hypothetical 0.280 km3 flank collapse directed southwestwards would trigger an initial wave 43 m in height that would reach the islands of Sertung, Panjang and Rakata in less than 1 min, with amplitudes from 15 to 30 m. These waves would be potentially dangerous for the many small tourist boats circulating in, and around, the Krakatau Archipelago. The waves would then propagate in a radial manner from the impact region and across the Sunda Strait, at an average speed of 80–110 km h21. The tsunami would reach the cities located on the western coast of Java (e.g. Merak, Anyer and Carita.) 35–45 min after the onset of collapse, with a maximum amplitude from 1.5 (Merak and Panimbang) to 3.4 m (Labuhan). As many industrial and tourist infrastructures are located close to the sea and at altitudes of less than 10 m, these waves present a non-negligible risk. Owing to numerous reflections inside the Krakatau Archipelago, the waves would even affect Bandar Lampung (Sumatra, c. 900 000 inhabitants) after more than 1 h, with a maximum amplitude of 0.3 m. The waves produced would be far smaller than those occurring during the 1883 Krakatau eruption (c. 15 m) and a rapid detection of the collapse by the volcano observatory, together with an efficient alert system on the coast, would possibly prevent this hypothetical event from being deadly. Most recorded historical tsunamis have a seismic more than 200 km from the collapse (Maramai origin, but such events may also be triggered by et al. 2005). The tsunami generated by the phenomena related to huge volcanic eruptions, 30 106 m3 Lituya Bay collapse in Alaska in such as large pyroclastic flows entering the water 1958 (Fritz et al. 2001) reached 60 m at 6 km later- (e.g. de Lange et al. 2001; Maeno & Imamura ally from the collapse and 30 m at 12 km. These tsu- 2007), submarine explosions (e.g. Mader & Gittings namis had very few fatalities as they occurred either 2006), caldera collapse (e.g. Nomanbhoy & Satake in isolated locations (Lituya Bay, Alaska) or during 1995; Maeno et al. 2006) or by a large, rapidly a period of no tourist activity (Stromboli). The sliding mass impacting the water (e.g. Tinti et al. largest lateral collapse of an island volcano recorded 1999, 2000, 2006; Keating & McGuire 2000; in historical times (c. 5 km3) took place during the Ward 2001; Harbitz et al. 2006; Fritz et al. 2008; 1888 eruption of Ritter Island (New Guinea), produ- Waythomas et al. 2009; Kelfoun et al. 2010). The cing witnessed waves of up to 10–15 m at tens to December 2002 17 106 m3 flank collapse of hundreds of kilometres from the source (Ward & Stromboli triggered a 8 m-high run-up on the coast Day 2003). With 15 000 fatalities, the tsunami of Stromboli, but had little effect on coasts located generated by the 1792 sector collapse of Mount From:Terry, J. P. & Goff, J. (eds) 2012. Natural Hazards in the Asia–Pacific Region: Recent Advances and Emerging Concepts. Geological Society, London, Special Publications, 361, 79–90, http:// dx.doi.org/10.1144/SP361.7 # The Geological Society of London 2012. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on March 12, 2012 80 T. GIACHETTI ET AL. Mayuyama in Ariake Bay (Kyushu Island, Unzen and daily seismic event statistics are used to deter- volcanic complex) was the second worst disaster mine the current alert level, on the basis of which in Japan, and the second deadliest volcanic Indonesian authorities decide about preventive tsunami (after that produced by the eruption of measures, sometimes prohibiting tourism around Krakatau in 1883). The failure was most probably the archipelago (Hoffmann-Rothe et al. 2006). triggered by a strong earthquake, and its volume One possible major hazard emerging from Anak was about 340 106 m3 (Michiue et al. 1999). Krakatau would be a tsunami triggered by a collapse Tsunami run-ups ranged from 8 to 24 m on the of its flank, as the volcano is partly built on a steep opposite side of Ariake Bay (Tsuji & Hino 1993). wall of the caldera resulting from the 1883 eruption. The 26–28 August 1883 Plinian eruption of A small tsunami (c. 2 m high) was experienced on Krakatau Volcano, and its subsequent tsunamis, Rakata Island in October 1981 during an awakening caused more than 35 000 casualties along the of Anak Krakatau (Camus et al. 1987). In the coasts of the Sunda Strait in Indonesia (Self & present study, we numerically simulate a sudden Rampino 1981; Simkin & Fiske 1983; Sigurdsson southwestwards destabilization of a large part of et al. 1991a, b). This eruption was one of the most the Anak Krakatau Volcano, and the subsequent powerful and devastating eruptions in recorded tsunami formation and propagation. We show history. Many tsunamis were produced during this results concerning the time of arrival and the ampli- approximately 2 day eruption, the largest one occur- tude of the waves produced, both in the Sunda Strait ring after 10 a.m. on the 27 August (Warton & Evans and on the coasts of Java and Sumatra. We then 1888; Yokoyama 1981). The leading wave reached discuss the relationships between the morphology the cities of Anyer and Merak on Java after 35– of Anak Krakatau, the locations of the surrounding 40 min, and after approximately 1 h for the city of islands, the bathymetry of the strait and the Bandar Lampung (Teluk Betung) on Sumatra. A triggered waves. tide gauge located near Jakarta (Batavia Harbour, Java) registered the wave arrival approximately 140 min after its inferred initiation at Krakatau Geography, population and infrastructures Island. Using the tsunami run-ups determined in the Sunda Strait along the coasts of Java and Sumatra (Verbeek 1885), the tsunami heights before run-up were esti- The Sunda Strait, in which Anak Krakatau Volcano mated to be about 15 m at the coastline all around lies, has a roughly NE–SW orientation, with a the Sunda Strait (Symons 1888). The generation minimum width of 24 km at its NE end between mechanism of these 1883 tsunamis is still contro- Sumatra and Java (Fig. 1). Its western end is deep versial and several processes may have acted suc- (,21500 m), but it shallows significantly as it cessively or together (Self & Rampino 1981; narrows to the east, with a depth of only about Yokoyama 1981; Camus & Vincent 1983; Francis 20 m in parts of the eastern end, making it difficult 1985). Based on low-resolution numerical simu- to navigate due to sandbanks and strong tidal lations, Nomanbhoy & Satake (1995) concluded flows. The numerous islands in the strait and the that a series of submarine explosions over a period nearby surrounding regions of Java and Sumatra of 1–5 min was the most probable source for the were devastated by the 1883 Krakatau eruption. major tsunami. Nevertheless, pyroclastic flows The eruption drastically altered the topography of formed by the gravitational collapse of the eruptive the strait, with approximately 12 km3 (DRE, dense columns are also a possible source for most of the rock equivalent) of ignimbrite being deposited tsunamis observed before and during the paroxysm around the volcano (Carey et al.