Earth and Planetary Science Letters 449 (2016) 382–394 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Giant submarine landslides on the Colombian margin and tsunami risk in the Caribbean Sea Stephen C. Leslie ∗ , Paul Mann Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, USA a r t i c l e i n f o a b s t r a c t Article history: Received 2 February 2016 Received in revised form 23 May 2016 Accepted 24 May 2016 Available online 13 June 2016 Editor: P. Shearer Keywords: mass transport deposit submarine slide seismic reflection Colombian Caribbean margin tsunami Caribbean Sea A series of three giant, previously unrecognized submarine landslides are defined on a 16,000 line km grid of multi-channel 2D seismic reflection profiles along the active margin of northern Colombia in the western Caribbean Sea. These deposits record the collapse and mobilization of immense segments (thousands of cubic kilometers) of the submarine slope and are comparable in scale to the largest known landslides on Earth. We show that the breakaway zone for these events corresponds to the tectonically over-steepened slopes of the Magdalena Fan, an extensive submarine fan composed of sediments sourced from the northern Andes and deposited by the Magdalena River. An over-pressured zone of weakness at the base of the gas-hydrate stability layer within the fan likely facilitates slope failure. Timing of these massive slope failures is constrained by well control and occurred from the mid-to-late Pliocene to mid-Pleistocene. To understand the tsunamigenic hazards posed by the recurrence of such an event today, we model the potential tsunami source created by a submarine landslide of comparable thickness (400 m) and lateral extent (1700 km 2 ) derived from the over-steepened upper slopes of the present day Magdalena Fan. Our modeling indicates the recurrence of an analogous slope failure would result in a major tsunami that would impact population centers along the Caribbean coastlines of Colombia, Central America, and the Greater Antilles with little advance warning.  2016 Elsevier B.V. All rights reserved. 1. Introduction Submarine landslides have the potential to cause unexpected or “surprise” tsunamis in regions not typically thought of as tsunami prone (Ward, 2001; Hornbach et al., 2010; Lo Iacono et al., 2012). When they occur, these tsunamis waves arrive in coastal areas with little advance warning and can devastate coastal communi- ties. For example, in 1998 a 7.1M w earthquake in Papua New Guinea triggered a submarine landslide of ∼4 km 3 which caused a catastrophic tsunami with local run-up heights of up to 15 m that killed more than 2200 coastal inhabitants (Heinrich et al., 2001; Tappin et al., 2008). While only 7% of tsunamis world- wide are thought to originate by submarine landslide or a com- bination of earthquake and landslide (National Geophysical Data Center, 2016), the destructive potential of these events is highest when they affect areas with large coastal populations uninformed and unprepared for tsunami hazards, such as the Caribbean Sea (Fig. 1). Hundreds of thousands of residents, tourists, and tourist- industry workers are potentially at risk from tsunamis around the densely populated urban and tourist areas of the Caribbean * Corresponding author. E-mail address: scleslie@uh.edu (S.C. Leslie). (von Hillebrandt-Andrade, 2013). Unfortunately, unlike earthquake generated tsunamis in seismically active coastal regions with long and meticulously maintained historical records (e.g. Japan), the infrequent nature of landslide tsunamis and the relatively brief historical records (∼500 yr) in the Caribbean region make under- standing the likelihood of these events in this area difficult (Ward, 2001; Harbitz et al., 2012). In the absence of historical records of tsunamis occurring along Colombian Caribbean margin it is nec- essary to investigate the history and magnitude of past tsunamis using the geologic record. In this study, a series of giant (>1000 km 3 ), previously un- recognized, Plio-Pleistocene age submarine landslide deposits are identified on seismic reflection records from the submarine Mag- dalena fan along the Caribbean margin of northern Colombia (Fig. 1). Our observations include the frequency, location, lateral extent, and thickness of the largest slope failures in the area. We use these observations as parameters for modeling the effects of a future tsunami produced by a similar event (Lo Iacono et al., 2012; Harbitz et al., 2014). Sediments resulting from submarine slope failures range in scale from tens of cubic meters to thousands of cubic kilometers and are classified as mass transport deposits (MTDs) (Weimer, 1989; Mulder and Cochonat, 1996). MTD depo- sition occurs by a variety of matrix-supported, mass movement http://dx.doi.org/10.1016/j.epsl.2016.05.040 0012-821X/ 2016 Elsevier B.V. All rights reserved.