unique from each other despite both being elongate class scours. The size and similar orientations of the 4 different scour types suggests that these are erosional features associated with currents of a turbulent, seasonal or tidal nature (Figures 3-5). Werner and Newton (1975) suggested that an increase in water turbulence from current-shoal interactions can facilitate erosion and create scour marks. The USGS carried out studies on similar features discovered proximal to sand banks off Rhode Island’s coast and found that the scours were likely to have been initiated by tidal currents ripping through the relatively shallow continental shelf waters, having been channeled by sand banks (Lawrence et al., 2016). Each scour type has a different predominant heading, as shown in the rose diagrams (Figures 3-5). These headings can be used to represent direction of ongoing erosion, and continued current interaction (Lawrence et al., 2016). The similarity of orientations at each site suggests that the different scours types may have been generated by currents specific to each study site (Figures 3-5 [rose diagrams], 8). The propagation of these scour marks can lead to scour features combining together, and perhaps different scour types may represent different stages in the evolution of larger-scale erosional features (Lawrence et al., 2016). The evolution of these scour features can be studied through the analysis and characterization of similar, proximal, scours. Further studies of interactions between scourtypes and scour propagation, could yield data crucial to understanding the directions and velocities of currents in this area, as well as the impact of current-bank interactions and their effects on the local biosphere.

METHODS • Kevin Sheehan was the chief scientist aboard the R/V Celtic

Explorer for expedition CV1701 from July 22 to August 6, 2017 Multibeam sonar bathymetric and backscatter intensity data were collected using a Kongsberg EM2040 transducer.

• Post-processing was performed with CARIS HIPS 10.2 and 10.4 to create 3D images as well as an 8m CUBE BASE surface, profiles, and backscatter intensity surfaces (Fig. 3-5).

• Quantitative data were collected using Google Earth Pro and CARIS Hips and Sips 10.2.

• Scours were outlined, and numbered. A method of classification/measuring was created to record the features’ geomorphologic data (Fig. 2).

• Statistical analyses were used to compare the geomorphic data (Fig. 7).

DISCUSSIONThe purpose of this study was to analyze and characterize the erosional scour features found on Labadie Bank using their geomorphological characteristics (Figure 1). The scours were visually and quantitatively separated into either a ‘pockmark’ or an ‘elongate’ scour class, based on comparing numerous measured variables, some of which showed significant correlation (Figures 7a-d). For each of the variable comparisons, several of the scour types showed a clustering of data points, indicating distinct morphologic differences. Type 4 scours are teardrop or elliptically shaped, and are only present in the Northeastern study site, NE-b. The aesthetic ‘greatest average width’ attribute, is a major factor in ‘pockmark’ classification (Figures 5, 7 a/d, 8). The uniqueness of Type 4 scours is also seen in the fact that the profiles of the Type 4 scours show shallow, flat, scours similar to those of Type 1, though the relative lengths of these two different scour types are vastly different (Figure 6). Type 4 and Type 1 scours differ in length symmetry and sinuosity despite having similar profile shapes (Figures 6, 7 b/e). Type 1 scours are the outlier group of the elongate scours (Figures 7, 8), whereas Type 2 scours are extremely variable in most circumstances excluding their elongate shape (Figure 7d, 8). Length symmetry and area comparisons show Type 3 scours are the ‘elongate scours’ most similar to the ‘pockmark’ scour class (Figure 7b/c, 8). The similarity between Type 1 and 2 scours is observable as both are more elongate than Type 3 scours (Figure 8). Type 1-3 scours are morphologically

BACKGROUNDLabadie Bank is an INtegrated Mapping FOr the Sustainable Development of Ireland's MArine Resource (INFOMAR) priority mapping area due to its impact on navigation and the regional fishing economy. The dynamic shape and size of this bank provide optimal conditions for fish habitat, while posing a possible navigation risk. With water depths ranging 63 to 137 m and an approximate length of 70km, this geographical feature interacts with currents and possibly storm wave bases. The interaction of this oblong, mounded bank with bottom currents was studied aboard the R/V Celtic Explorer (cruise CV1701) during a seabed mapping survey in summer 2017. Areas with relief in topography like Labadie Bank or Jones Bank are found to generate ‘internal wave packets’ as the topography interacts with seasonal stratified flows to result in mixing of the water column. This turbulence may lead to pockets of high productivity (Palmer et al. 2013). This mapping survey also revealed unique scour-like features along the flanks of the bank. These features were found on the northern half of Labadie Bank, and vary in size, orientation, and shape. The purpose of this study is to create a technique for the classification of these features and attempt to determine the factors responsible for the variations in shape and orientation.

Geomorphological Analysis and Characterization of Labadie Bank in the Celtic Sea Luke Hollahan and Dr. Leslie Sautter

Dept. of Geology and Environmental Geosciences, College of Charleston

ACKNOWLEDGEMENTS ---This research would not have been possible without INFOMAR who collected the data on board the R/V Celtic Explorer. Additionally, we would like to thank CARIS for Academic Partnership, and the support from the School of Science & Math. This project was conducted as part of the College of Charleston BEAMS Program.

R/V Celtic Explorer

RESULTSBackscatter return intensity images highlight four different types of erosional scour features, each of which seem to be concentrated in a confined area or study site (Figure 1, 3-5). These scours all appear to have very high intensity relative to the surrounding seabed, indicating hard-packed or semi-consolidated sediment, and topographic relief (Figures 3-5). Profiles transecting the major scour features at each site show differences in geomorphology between ‘pockmark’ and ‘elongate’ scours (Figure 6). The collected data and statistical analyses determined similarity or differences between the different scour types (Figure 7). Major differences in overall shape distinguish the ‘pockmark’ from the ‘elongate’ class (Figures 7a/e, 8). Similar trends with variable statistical grouping show Type 1 scours are significantly different from the rest of the ‘elongate’ class scours (Figure 7). Type 2 scours are statistically linear regardless of their variable measurements (Figures 7d, 8). Type 3 scours are the ‘elongate’ scours most related to the Type 4 ‘pockmark’ scour (Figures 7b/c, 8). Unlike other scour types, Type 4 scours become narrower and less sinuous as their along axis length increases (Figures 7a/e). Heading data from rose diagrams show that these scour features may be the result of regional current driven erosion (Figures 3-5).

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Along Axis Length (green) - length along the feature’s (valley) axisCrow Flies Length (red) - length from head to tailWidth (dashed white) - at the widest point, perpendicular to the ‘Length’Head Length (black arrow) - length from head to the ‘width’ lineTail Length (black arrow dashed) - length from ‘width’ line to end of tailTail Angle - angle at which the tail ‘opens’Heading - orientationArea - area covered by feature (m2)Tail Width (white solid) - width of the tail halfway between the ‘Width ‘ marker and the end of the tail Sinuosity - along axis length/crow flies length

Measurement System

Figure 2: Measuring techniquefor scour classification of elongate scours (left) and pockmark scours (right). Measurement parameters at described at left.

ABSTRACTAs part of the INFOMAR program, the Marine Institute of Ireland and the Geological Survey of Ireland plan to have mapped the entire continental shelf surrounding Ireland using high resolution multibeam by 2020. One of the recent surveys was conducted aboard the R/V Celtic Explorer from July 22 to August 6, 2017. The study area was located off Ireland’s southeastern coast. Sonar data were post-processed to generate bathymetric and backscatter intensity surfaces. Much of the study area is comprised of a large sand bar called Labadie Bank, where depths fluctuate between 63 m at the bank crest to approximately 135 m in surrounding basin. Labadie Bank has an elongate elliptical shape along with several geomorphological features, including four different types of large scours. These geomorphological features are clumped in study sites on different locations on Labadie Bank. The purpose of this study is to interpret the geomorphological features of the Labadie Bank region and to create a classification system for the four different scour types observable.

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REFERENCES• http://www.columbia.edu/dlc/cup/ricci/ri

cci16.html• Lawrence J. Poppe, Katherine Y.

McMullen, William W. Danforth, Mark A. Blankenship, Andrew R. Clos, Kimberly A. Glomb, Peter G. Lewit, Megan A. Nadeau, Douglas A. Wood, and Castleton E. Parker. (2016, December 7). USGS Open-File Report 2014-1012: Combined MultibeamBathymetry Data from Rhode Island Sound and Block Island Sound – A Regional Perspective. Retrieved January 21, 2018, from https://pubs.usgs.gov/of/2014/1012/html/bathy.html

• Palmer, M. R., Inall, M. E., & Sharples, J. (2013, June 26). The physical oceanography of Jones Bank: A mixing hotspot in the Celtic Sea. Retrieved February 07, 2018, from https://www.sciencedirect.com/science/article/pii/S0079661113000979#f0010

• Werner and Newton. (1975, June). The pattern of large-scale bed forms in the Langeland Belt (Baltic Sea). Retrieved January 21, 2018, from https://www.researchgate.net/publication/238375425_The_pattern_of_large-scale_bed_forms_in_the_Langeland_Belt_Baltic_Sea

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South Western Study Site (SW)Figure 5: Backscatter intensities for SW-a and SW-b sites (Fig.1), showing 3D bathymetry and current rose diagrams as well as magnified views of the scours within the site. These scours are classified as elongatescours despite their complex morphology, which is similar regardless of the spread-out nature of the scour features. These elongate scours have headings in a predominantly SE direction (215⁰-235⁰ or 250-270⁰) down the Northwestern facing slope of Labadie Bank in the SW study site. They differ from other elongate scours in their complex morphology and lack of width.

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Figure 3: Backscatter intensity of sites NE-a and NE-b (Fig. 1), showing magnified views as well as bathymetry details and current rose diagrams. Scours measured are indicated by red numbers. Two distinct scour morphologies were identified at this site: Elongate scours at NE-a, and Pockmark scours at NE-b. Current rose figures indicate that NE-a scours are oriented in a predominantly N-S direction (0⁰-10⁰) down Labadie Bank’s Northern slope, whereas NE-b scours are orientated NW/SE at the bank top (35⁰-55⁰) and on the bank’s north slope (195⁰-215⁰).

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Figure 4: Backscatter intensity of site CS-a (Fig. 1) with 3D bathymetry and a current rose diagram and magnified view depicts a third type of scour morphology. These scours are also elongate with headings in a predominant SE direction (235⁰-255⁰) near the central section of the bank top. They differ from elongate NE-a scours in sinuosity as well as overall size; and from NE-b scours due to length vs width ratios indicative of elongate scours.

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Figure 1. Labadie Bank CUBE BASE surface (8m resolution) shows the Northeastern (NE), Central (CS), and Southwestern (SW) study sites. The bank lies south of the south Irish coast (upper left). Study site details (right) show areas of scour features examined (boxes). Note varying depth scales.

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Figure 7. Graphical representation of significant data correlations and relationships from statistical analysis and data clustering (colored ovals). Only significant linear relationship R2 values are shown.7a) The morphological difference between Type 4 scours, as seen in the NE site, and the different classes of elongate scours seen across Labadie Bank. 7b) Length symmetry measurements highlight the linear symmetry of scour Types 1 and 3, and highlights the asymmetry of Type 2 scours. 7c) Length:Width is a measure of elongation, explaining the near-origin values for Type 4 ‘pockmark’ scours. A significant positive correlation exists between absolute depth and elongation only for scour Types 1 and 3.Types 4 and 3 cluster well. 7d) A comparison of scour average width with area (l x w), indicates the difference between ‘pockmark’ (Type 4) and ‘elongate type’ (Type 1-3) scours. Type 4 scours are widest on average while Type 1 scours are the narrowest. 7e) No correlation exists between sinuosity and along axis length for any scour type. Type 4 scours have variable sinuosity with little along axis length variation. Type 1 scours may have a slight decrease in sinuosity with axis length.

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Classification of Scour MorphologiesFigure 8: Based on both visual and numerical data, four distinct types of scour morphologies were found on Labadie Bank. These four scour types are divided into either ‘elongate’ scours (Types 1-3), or ‘pockmark’ scours (Type 4).

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