The Late Tertiary-Quaternary onshore tsunami record of nothern Chile and southern Peru: towards the recognition of diagnostic features of onshore tsunami deposits (short title: Chile-Peru tsunami deposits)
Final Report Abstract
The Peru-Chile-Trench is one of the most active seismic areas in the world. In order to learn about the long term tsunami history of Peru and northern Chile, and to estimate recurrence intervals, we surveyed about 3000 km of coastline between Tumbes in Northern Peru and Antofagasta in Northern Chile. The primary purposes of this study are the identification of typical sediment structures displayed in modern tsunami deposits along the coast of Peru and Chile, and the application of the results to paleo-deposits. Sites of recent tsunami events, such as the 1996 Chimbote, 2001 Camana and 2007 Pisco tsunami, were also resurveyed to gain information on the preservation potential of tsunami deposits in arid coastal environments. Onshore tsunami deposits were studied in trenches and boreholes down to depths of 3 m. The event layers and background sediments were sampled and analyzed. Grain-size distributions were used to obtain information on the number and type of sediment sources. We analyzed microorganisms (e.g., foraminifera) for the inference of water depths of sediment entrainment by the respective tsunami. Additionally, sedimentary structures that reflect different conditions within the tsunami flow and have the potential to record the flow parameters, e.g. flow directions or type of transport, of the overland flow that created them, were used to describe the processes acting during tsunami inundation. The encountered sediments were dated with optically stimulated luminescence dating (OSL). Magnitudes of historical events were calculated using inverse tsunami models. Preserved siliciclastic onshore tsunami sediments displayed various characteristics: (1) (graded) layers of coarse sand, some of them including shell fragments or pieces of rock, (2) (graded) shell layers, (3) heavy mineral accumulations and (4) mud caps or mud balls. Both runup and backwash sediments were preserved, as indicated by flow structures and sediment composition. In southern Peru two previously unknown paleotsunami deposits and events were dated by OSL as 1983 ± 231 B.P. and 2255 ± 367 B.P. A third deposit dated as 1641 ± 26 B.P. probably coincides with a known event, the 1647 tsunami of southern Peru. In combination with the historical record our data point to a potential recurrence interval for major tsunamis of ca. 270 years. The preservation potential of onshore tsunami deposits is determined by complex interactions of several erosional and depositional processes. We were able to show that the quantity of preserved sediments decreases with the time elapsed since the event. No remains of the Chimbote tsunami were left eleven years after the event, only half of the sediments of the Camana tsunami were left six years later, and numerous deposits were still present one year after the Pisco-Paracas tsunami. Regarding sediment composition, fine grained deposits generally have a lower preservation potential compared to coarse grained deposits which are less prone to aeolian erosion. Muddy deposits showed a moderate to high preservation due to the cohesion of the mud particles. Finally, we re-evaluated previously described submarine tsunami deposits in Northern Chile. Our investigations show that these sediments are not the result of tsunami backwash in a shallow marine environment, but rather are distal alluvial fan and fan delta deposits.
Publications
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(2008). Historical tsunami events along the coast of Peru – sedimentology and dating. 2nd International Tsunami Field Symposium, Brindisi (Italy), 22-28 September 2008
Spiske, M., Piepenbreier, J., Benavente, C., Kunz, A., Bahlburg, H.
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(2008). Inversion of flow depth and speed from tsunami deposits using TsuSedMod. Eos Transactions. American Geophysical Union, Fall Meeting Supplement
Spiske, M., Weiss, R., Bahlburg, H.
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(2008). Observaciones preliminares acerca los depósitos de tsunami en el sur del Perú. XIII Congreso Latinoamericano de Geología y XIV Congreso Peruano de Geología, Lima (Peru), resumenes, 29.09.-03.10.2008
Benavente, C., Spiske, M., Piepenbreier, J.
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(2008). Storm and tsunami deposits in light of cyclone Nargis, Birma, May 2 and 3, 2008. 26th IAS Meeting of Sedimentology, Bochum, Germany, 01.-03.09.2008
Bahlburg, H.
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(2008). The role of porosity in discriminating between tsunami and hurricane emplacement of boulders - a case study from the Lesser Antilles, southern Caribbean. Earth and Planetary Science Letters 268, 384-396
Spiske M., Böröcz, Z., Bahlburg, H.
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(2009). A review of criteria for the distinction of high energy wave events. 27. Jahrestagung des Arbeitskreises „Geographie der Meere und Küsten“, Kiel, 24.-26.04.2009
Spiske, M., Bahlburg, H., Deicke, M., Steffahn, J.
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(2009). Sedimentology of tsunami deposits along the coast of Peru. 21st Colloquium on Latin American Geosciences. Lateinamerika Kolloquium 2009, Göttingen, 07.04.-09.04.2009
Piepenbreier, J., Spiske, M., Benavente, C., Steffahn, J., Bahlburg, H.
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(2010). A note on the onshore preservation potential of siliciclastic tsunami deposits - examples from coastal Peru. EGU Annual Meeting, Vienna, Austria, Geophysical Research Abstracts 12, EGU2010-8927-1
Spiske, M., Piepenbreier, J., Bahlburg, H., Benavente, C.
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(2010). Comment on „Sedimentary features of tsunami backwash deposits in a shallow marine Miocene setting, Mejillones Peninsula, northern Chile, Sedimentary Geology, 178(3/4), 259-273” by Cantalamessa and Di Celma (2005). Sedimentary Geology 228, 77-80
Bahlburg, H., Spiske, M., Weiss, R.
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(2010). The application of the TsuSedMod inversion model for the estimation of flow depth and speed of the 2004 Sumatra and 2006 Java tsunamis and implications for paleo-tsunami research. Sedimentary Geology 224, 29-3
Spiske, M., Weiss, R., Bahlburg, H., Roskosch, J., Amijaya, H.
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(2010). Why in dubio pro tsunami deposits does not work: Two examples from northern Chile. 18th International Sedimentological Congress, Mendoza, Argentina
Bahlburg, H., Spiske M., Weiss, R.
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(2010). Why in dubio pro tsunami deposits does not work: Two examples from northern Chile. EGU Annual Meeting, Vienna, Austria, Geophysical Research Abstracts 12, EGU2010-10802
Bahlburg, H., Spiske M., Weiss, R.
