Lateral variability in strain along a mass-transport deposit (MTD) toewall: a case study from the Makassar Strait, offshore Indonesia

Contractional features characterise the toe domain of mass-transport deposits (MTDs). Their frontal geometry is typically classified as frontally-confined or frontally-emergent. However, it remains unclear how frontal emplacement style and contractional strain within an MTD can vary along strike. We use bathymetry and 3D seismic reflection data to investigate lateral variability of frontal emplacement and strain within the toe domain of the Haya Slide in the Makassar Strait. The slide originated from an anticline flank collapse, and the toe domain is characterised by a radial fold-and-thrust belt that reflects southwestwards emplacement. The frontal geometry of the slide changes laterally. In the S, it is frontally-confined, associated with a deep, c. 200 mbsf, and planar basal shear surface. The frontal geometry gradually changes to frontally-emergent in the W, associated with a shallow, c. 120 mbsf, and NE-dipping, c. 3o, basal shear surface. Strain analysis shows c. 8-14% shortening, with cumulative throw of the thrusts that increases along strike westwards from c. 20-40 to c. 40-80 m. We show that even minor horizontal translation of MTDs (c. 1 km) can result in marked lateral variability in frontal geometry and strain within the failed body, which may influence their seal potential in petroleum systems

Extreme erosion by submarine slides

Submarine slides (including slides, slumps, and debris flows) pose major geohazards by triggering tsunami and damaging essential submarine infrastructure. Slide volume, a key parameter in hazard assessments, can increase markedly through substrate and/or water entrainment. However, the erosive potential of slides is uncertain. We quantified slide erosivity by determining the ratio of deposited (Vd) to initially evacuated (Ve) sediment volumes; i.e., slides that gain volume through erosion have a Vd/Ve ratio >1. We applied this method to the Gorgon slide, a large (500 km3 ), seismically imaged slide offshore northwestern Australia, and reviewed Vd/Ve ratios for 11 other large slides worldwide. Nine of the 11 slides have Vd/Ve > 1 (median value = 2), showing emplaced volumes increased after initial failure. The Gorgon slide is the most erosive slide currently documented (Vd/Ve = 13), possibly reflecting its passage across a highly erodible carbonate ooze substrate. Our new approach to quantifying erosion is important for hazard assessments given substrate-flow interactions control slide speed and runout distance. The variations in slide volume also have important implications for submarine infrastructure impact assessments, including more robust tsunami modeling