Chapter 35Morphological Expression of SubmarineLandslides in the Accretionary Prismof the Caribbean Continental Marginof Colombia

Javier Idarraga-Garcıa and Carlos A. Vargas

Abstract Morphological analyses of �14,500 km2 of high-resolution-bathymetricdata in the Caribbean continental margin of Colombia has allowed us to identifysubmarine landslides in the Sinu Accretionary Prism (SAP) and Magdalena subma-rine fan (MSF) areas.

In the MSF area most of submarine failures are disintegrative, i.e. with noobvious deposit near or at the base of the scar, and are related to a system of canyonsbelonging to the Magdalena turbidite system and to an abrupt slope break at theborder of the continental shelf. Landslides in the SAP area are mainly associated tothe steeper flanks (12–18ı) of anticline-related ridges. In many cases, the associatedlandslide deposits are buried by subsequent sediments related to broad fans formedin the mouth of channels and canyons. The cohesive landslides identified exhibitblocky deposits with rubble masses up to 50 m high and runout distances between3.6 and 11 km.

Morphometric analyses of scarps allowed us to calculate landslides ages infunction of the constant � of diffusivity. Estimations using a � value of 0.015 m2y�1

suggest ages ranging between 13.8 and 9,761.9 ky for the MSF and ages between12.2 and 1,031.8 ky for the SAP.

Keywords Submarine landslides • Canyons • Anticline-related ridges •Morphometric dating • Colombian Caribbean

J. Idarraga-Garcıa (�)Graduate Program of Geophysics, Universidad Nacional de Colombia, Bogota, Colombiae-mail: jidarragag@unal.edu.co

C.A. VargasDepartment of Geosciences, Universidad Nacional de Colombia, Bogota, Colombiae-mail: cavargasj@unal.edu.co

S. Krastel et al. (eds.), Submarine Mass Movements and Their Consequences, Advancesin Natural and Technological Hazards Research 37, DOI 10.1007/978-3-319-00972-8 35,© Springer International Publishing Switzerland 2014

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392 J. Idarraga-Garcıa and C.A. Vargas

35.1 Introduction

The mapping and characterization of submarine failures have attracted muchattention in the past two decades, including with regard to their role as potentialgeohazards for marine and coastal infrastructure. The active Colombian Caribbeancontinental margin is characterized by a rough morphology and the presence offour active deltas fed by large Andean rivers. These features provide a priori highsusceptibility to the occurrence of landslides with a wide range of sizes and types.Submarine landslides are triggered either by an increase in the driving stresses, adecrease in strength, or a combination of the two (Lee et al. 2007). The followingpossible triggers show the interplay of these factors: sediment accumulation,erosion, earthquakes, volcanism, waves, gas and gas hydrates, diapirism and humanactivity (Moore et al. 1989; Hampton et al. 1996; Mulder and Cochonat 1996;McAdoo et al. 2000).

The main objective of this paper is to present the morphological characteristicsof the submarine landslides in the MSF and the SAP areas (Fig. 35.1) and discusstheir possible origins and ages.

Fig. 35.1 Location of the studied areas (SAP and MSF) and the instrumental seismicity withmagnitudes greater than 4.5. Dashed line boxes indicate Figs. 35.2 and 35.3. Black bold linesindicate major structures

35 Morphological Expression of Submarine Landslides in the Accretionary Prism. . . 393

35.2 Geologic Setting of the Study Area

35.2.1 Seismotectonic Setting

The Colombian Caribbean is located in a complex zone formed by the interactionbetween South American and Caribbean plates (Vargas and Mann 2013). TheCaribbean oceanic plate is being subducted beneath the northwestern edge of theSouth American plate. The South Caribbean Deformed Belt represents the boundarybetween these two plates and corresponds to a NW-verging highly deformedsequence of sediments (Vinnels et al. 2010). The SAP is the offshore part of thebelt and is made up of deformed sedimentary rocks that range in age from MiddleEocene to Late Oligocene (INGEOMINAS 2003).

Seismicity in the region is mainly located onshore. According to the ColombianNational Seismological Network, there have been 8,821 earthquakes with Mwranging from 2.5 to 7.3 and focal depths from 10 to 280 km in the period 1973–2013. Four of these events occurred close to the study zone with Mw >6 and focaldepths <70 km (Fig. 35.1).

35.2.2 Morphology of the Colombian CaribbeanContinental Margin

The Colombian Caribbean continental margin has a pronounced relief, in which twomain elements are recognized (Fig. 35.1). The continental slope extends from 200to 3,500 m depth and has a width less than 100 km (Lopez 2005). The continentalshelf has a maximum depth of 200 m and is 1,100 km-long from the Gulf of Urabato the peninsula of La Guajira; its width varies from 5 km around the city of SantaMarta to over 50 km offshore the Gulf of Morrosquillo (Lopez 2005).

In the study area, the margin can be divided into two contrasting sectors: the SAP,from the Gulf of Uraba to immediately north of the Gulf of Morrosquillo and theMSF, between the cities of Cartagena and Barranquilla (Fig. 35.1).

The SAP area exhibits typical flow geoforms as channels and canyons, andstructural geoforms such as ridges and escarpments. Strong tectonic activity ismanifested by the presence of NE-SW-oriented scarps and ridges related to axialzones of anticlines (Flinch 2003).

The MSF is a turbiditic system originated by the accumulation of the sedimentsdelivered by the Magdalena River since Middle Pliocene (Ercilla et al. 2002). Thecontinental shelf does not exceed 5 km in width so much of the sediment deliveredby the river is directly deposited on the continental slope through a system ofsubmarine canyons.

394 J. Idarraga-Garcıa and C.A. Vargas

35.3 Data and Methods

Multibeam bathymetric data was acquired in 2002 aboard the R/V Baruna Jaya IIIusing both ResonSeaBat 8160 (50 kHz) and Simrad EM12D (13 kHz) systems,and in 2006 aboard the M/V Ocean Endeavour using both Simrad EM1002(93/98 kHz) and Simrad EM120 (11.25/12.75 kHz). Digital Terrain Models weresubsequently created from the raw data with spatial resolutions between 50 and25 m. These models were used to identify and describe submarine landslides. Weused the nomenclature of McAdoo et al. (2000) to determine the type of massmovement.

We performed a quantitative scarp analysis in order to constrain a range of agesfor the occurrence of the failures. In this sense, dating was carried out following themethodology of Hanks (2000) by applying a diffusion equation under transport-limited conditions. This equation relates the change in elevation to time usinga proportionality constant � of diffusivity [L2T�1] and measurements associatedto the fan-slope angle (� f ), the scarp-slope angle (� s) and the effective verticaldisplacement of the scarp (2a).

35.4 Results

35.4.1 MSF Area

The area offshore of the current mouth of the Magdalena River is cut by a submarinecanyon system through which sediments are conducted to abyssal depths. Basedon bathymetric data, we differentiated three parallel canyons bounded by a seriesof structural highs; these canyons are incised by 260–400 m into the continentalslope (Fig. 35.2). Most of the failures identified are disintegrative, i.e. the depositsoriginated from the landslide were probably transported downstream through thecanyons or are buried by subsequent mass flow deposits (Fig. 35.2). Otherwise, wedistinguished two cohesive landslides in this area: one associated with the easterncanyon and the other with the central one (Fig. 35.2).

The eastern canyon landslide has an area of 72.6 km2; the headscarp is locatedat a depth of �950 m and has an average height of 235 m and a slope of 13ı. Thescar is 341 m high and there is a deposit at its base which is evidenced by a roughsurface composed of angular blocks with maximum height of 40 m (Fig. 35.2); themorphology of the scar is complex, with several arcuate indentations especially inthe SW part, suggesting that the whole area of the scar does not correspond to asingle event for the blocky deposit, but rather, to multiple events. The maximumrunout distance is 11 km until the debris abuts a structural high (Fig. 35.2).

35 Morphological Expression of Submarine Landslides in the Accretionary Prism. . . 395

Fig. 35.2 (A) Bathymetry offshore of the Magdalena River current mouth. Two cohesive land-slides are marked by the solid red line. Black box indicates zoom shown in (B). (B) Zoomview of the cohesive landslides present in the MSF. Solid black lines indicate the headscarpsand the dashed yellow lines outline the blocky deposits. Red arrows point to some disintegrativelandslides. (C) Bathymetry west of the current mouth of the Magdalena River. �t values are shownin parentheses next to the respective profile. MFD mass flow deposits, R ridge, EC eastern canyon,CC central canyon, WC western canyon, BD blocky deposit, CH channels, LChC leveed channelcomplex (For location see Fig. 35.1)

396 J. Idarraga-Garcıa and C.A. Vargas

The slope failure associated with the central canyon has an area of 5.8 km2; itsheadscarp is 1,200 m deep and reaches an average height of 74 m and a slope of22ı; the scar is 266 m high and exhibits a regular morphology; there is a depositat the base of the scar which surface shows an intermediate roughness given by thepresence of rubbles (Fig. 35.2); the runout distance reaches 3.6 km (Fig. 35.2).

The zone located westward of the current mouth of the Magdalena River ischaracterized by the presence of leveed channel complexes and large-scale massflow deposits on the continental slope. All the landslides are associated with gullies,channels and canyons present on the border of the continental shelf that are thefeeder of the mass flow deposits downslope (Fig. 35.2). The slope gradient at theshelf edge ranges between <1ı and 5.6ı.

Regarding the analysis of the 50 scarps (two cohesive and 48 disintegrativelandslides), the measurement of � s, � f and 2a allowed estimating ›t. Calculatedvalues range between �207.1 and �14,6427.8 m2 (Fig. 35.2), which is equivalentto an age range of 13.8–9,761.9 ky (see Sect. 35.5 below).

35.4.2 SAP Area

Most of the submarine landslides in the SAP are related to flanks of anticlines thatcontrol formation of ridges extending to a depth of 3,000 m (Fig. 35.3). These ridgesexhibit an asymmetric cross section with the steeper seaward flanks sloping between12ı and 18ı. There are failures on the walls of some submarine canyons located tothe north of the area. These canyons have their headwaters in the middle of thecontinental slope and extend cutting a series of ridges until ending at 2,500 m waterdepth, where they form submarine fans in several ridge-bounded intraslope basins(Fig. 35.3). The distal sector of the canyons shows a large number of disintegrativelandslides in their walls that give them an asymmetrical U-shaped cross section.

The landslides associated with the ridges are both cohesive and disintegrative.These two types of failures are more distributed towards the middle continentalslope where the appearance of the margin is very rough (average slope angle of15ı). In contrast, the margin tends to be smoother on the upper slope, as there arealmost no landslides (Fig. 35.3).

We focused on the detailed description of the three cohesive landslides bestimaged in the bathymetry (Landslide 1, Landslide 2 and Landslide 3) (Fig. 35.4).

35.4.2.1 Landslide 1

This failure is associated with the outermost ridge of the SAP and has an area of90.8 km2. The headscarp has a NNW-SSE-oriented arcuate shape with a slope of�20.6ı; this feature has a height of �316 m and is located in 2,100 m water depth(Fig. 35.4). The scar has a maximum height of 750 m and exhibits a very complexgeometry which suggests the occurrence of multiple failure events. A blocky deposit

35 Morphological Expression of Submarine Landslides in the Accretionary Prism. . . 397

Fig. 35.3 Bathymetry of the SAP where a set of anticline-related ridges is present in thecontinental slope. Red lines indicate cohesive landslides highlighted in Fig. 35.4 (black box). ›tvalues are shown in parentheses next to the respective profile

is present at the base of the scar where the rubble masses are evidenced as irregularangular-shaped bathymetric highs reaching maximum heights of 50 m; this depositextends to a depth of 2,915 m and has a maximum runout distance of 6.5 km(Fig. 35.4).

398 J. Idarraga-Garcıa and C.A. Vargas

Fig. 35.4 (A) Detail of the landslides L1, L2 and L3 (red lines) in the SAP. L2 and L3 are frontallyconfined by ridges. The respective profiles are shown to the right. The white line AB indicates thelocation of seismic profile shown in (B). Red arrows point to some disintegrative landslides. (B) 2Dseismic profile modified from Vinnels et al. (2010) where the main features of L2 are highlighted.R ridge, ISB intraslope basin, MFD mass flow deposit, BD blocky deposit, C canyon

35.4.2.2 Landslide 2

This landslide has an area of 48.1 km2. Its headscarp exhibits a rectilinear trendoriented NS and has a height of �248.2 m with a slope of 20.4ı; it is located at1,400 m water depth (Fig. 35.4). The scar is less complex than of the Landslide 1,indicating that it could be product of a single mass wasting event; its height is 496 m.The deposit caused by this event is frontally confined by the presence of a ridge atits downslope end and extends to a maximum depth of 2,730 m with a maximumrunout distance of 11 km. Its appearance is rougher than Landslide 1 due to thepresence of many angular-shaped rubble deposits rising up to 40 m (Fig. 35.4).

35.4.2.3 Landslide 3

This landslide has an area of 30.8 km2. The headscarp has a slightly arcuateappearance oriented NNE to NNW with a slope of 17.1ı; it is located at 875 m

35 Morphological Expression of Submarine Landslides in the Accretionary Prism. . . 399

water depth and has an average height of 132.6 m (Fig. 35.4). The scar has a heightof 566 m and its appearance is similar to the Landslide 2, suggesting that it may alsobe the result of a single event of mass wasting. The associated deposit has a runoutdistance of 8 km and is frontally confined by the presence of a ridge. The presenceof some angular up to 30 m high blocks results in an intermediate surface roughness(Fig. 35.4).

The ›t values obtained from the morphometric analysis of 41 scarps (threecohesive and 38 disintegrative failures) range between �182.9 and �15,476.3 m2

(Fig. 35.3). According to our approach (see Sect. 35.5 below) these values areequivalent to an age range of 12.2–1,031.8 ky.

35.5 Discussion and Conclusion

35.5.1 Origin of the Landslides

The origin of the landslides described in the MSF is related to the sedimentarydynamics that characterize the evolution of the Magdalena River delta. Thishypothesis is supported by the fact that the MSF is an active turbidite systemsince the Middle Pliocene (Ercilla et al. 2002). Modern offshore instability of thissystem is well documented by the numerous submarine cable breaks that haveoccurred since the 1950s (Heezen 1956). The system is fed by the Magdalena Riverwhich is considered the most important river of Colombia with a sediment load of144 � 106 t yr�1 (Restrepo and Kjerfve 2004) and whose evolution has been markedby several migrations of its mouth over time (Ercilla et al. 2002). The vast majorityof sediments brought by the river are deposited on the continental slope through acanyon system, this being a preconditioning factor for generating mass movements.This adds to the fact that the MFS is located in a tectonically active area where therehave been several earthquakes with magnitudes greater than 5 (Fig. 35.1).

The failures present in the SAP are associated with anticlines-related ridges.Here the preconditioning factor for the generation of landslides is the steep slopes(between 12ı and 18ı) on the seaward-flanks of the ridges, in contrast to themore gentle slopes on the opposite flanks (4–10ı). The orientations of the scarsslopes have a preferential NW direction product of the landslide occurrence on thewestward-oriented steeper flanks of the ridges.

35.5.2 Approach to the Age of Landslides

We presented ›t values obtained from the morphometric analyses of 91 profilesthroughout the study zone. Nowadays there is no consensus on the constant › valuesfor underwater environments, which can range up to several orders of magnitude.

400 J. Idarraga-Garcıa and C.A. Vargas

Mitchell (1996) reported a value of �0.007 m2y�1 for the Galapagos spreadingcenter. McAdoo and Simpson (2005) suggest values ranging between 10�3 and10�4 m2ky�1 for slides on continental slopes. On the other hand, Vargas et al. (2012)attempted to date the Mira submarine canyon (Colombia) and obtained that the mostprobable › values range between 0.001 and 1.33 m2y�1 for an event occurred in3,200 y BP. However, Ratzov et al. (2012) using other methods suggested that theMira canyon age may range between 53 and 67 ky. According to this, the › values inthe canyon area oscillate between 0.015 and 0.057 m2y�1, which are consistent withthe range suggested by Vargas et al. (2012). We tested these new limits of › valueto calculate ages. Estimations using a › value of 0.015 m2y�1 suggest landslidesages ranging between 13.8 and 9,761.9 ky for the MSF and ages between 12.2 and1,031.8 ky for the SAP. The large contrast of the results suggests a complex slopedynamics in the two study areas. However, this work is one of the first attempts todate the submarine landslides in the Colombian Caribbean.

Acknowledgments This work was conducted under the Seismotectonic Research of the GraduateProgram of Geophysics of the Universidad Nacional de Colombia. The authors are grateful tothe Assigned Editor Dr. David Volker and the reviewers Dr. Gueorgui Ratzov and Dr. GeoffroyLamarche. We also thank ANH-INVEMAR for giving us the permission to use the bathymetricdatabase. We are grateful to the COLCIENCIAS Doctoral Fellowship Program as well.

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