Applying quantitative methods to identify and distinguish between extensional and compressional ridges in subaqueous landslide deposits

Morphometric features within subaqueous landslide deposits provide critical information about the process of failure – a factor that is directly linked to the hazard potential of a landslide. However, some morphometric features, such as compressional and extensional (spreading) ridges, have similar geomorphology even though they form through very different processes. Identification and classification of these ridges in subaqueous landslide deposits is typically carried out manually and, as such, is heavily dependent on interpreter experience and bias. In this study, we make use of bedform analysis techniques typically used to identify seafloor features, such as ripples and dunes, to quantitatively characterize and distinguish between spreading and compressional ridges in subaqueous landslide deposits in a variety of settings, both lacustrine and submarine. Our approach involves identifying local maxima and minima, grouping them using neighbourhood analysis, and then calibrating these ridges using a series of closely-spaced perpendicular profiles following existing methods for bedform analysis. We then compare the metrics (including wavelength, height, slope, symmetry, and sinuosity) of the two kinds of ridges, and use these to distinguish between them. The application of quantitative, semi-automatic methodology such as this is critical to enable a move towards a less subjective interpretation of subaqueous landslide deposits, and to ensure accurate identification of features formed through different morphological processes.