Bathymetric and Geomorphological Analysis of Island,

Trey Gillespie and Dr. Leslie Sautter R/V Celtic Department of Geology and Environmental Geosciences, College of Charleston Voyager ABSTRACT Figure 1. Location of Inishmore Island, Ireland. 2D BASE surfaces Bathymetric surveys were conducted just offshore of Inis Mór A of the study areas are overlain Island on Ireland’s west-central coast, by the Marine Institute on an Admiralty Chart of the North R/V Celtic Voyager. Data were post-processed using CARIS HIPS Aran Island region off the central Study and SIPS 9.1 to create both 2D and 3D bathymetric surfaces. The Figure 2. 3D BASE surfaces of west coast. Area study site is a glacio-karstic limestone landscape. Analysis of the B the North Study bathymetry supports the interpretation of lithified marine North Study Area (top), and N sediment exposure above sea level, followed by erosion, and Area the Southwest- weathering since the Neogene Epoch, 23 Ma. Glaciers Southeast Study Areas. Letters A-F smoothed the exposed surfaces from 2 Ma to 18 Ka. Faulting / F and fracturing along the continental shelf showcases the E indicate the shore-normal limestone, highlighting its glacio-karstic characteristics. The D profile start purpose of this study is to use bathymetric analysis to map and Southwest C points (see Fig. 3, Study Area characterize the submerged limestone strata that are seen below). Bay exposed subaerially on Inishmore. of Ireland and Geological Southeast Survey of Ireland as part of the INFOMAR project. Data were Study Area collected from May to June 2014 using a Kongsberg EM2040 multibeam echosounder aboard the R/V Celtic Voyager.

BACKGROUND Shore-Parallel Profiles Inishmore Island sits at the mouth of Galway Shore-Normal Profiles and Geomorphology G G’ Bay in Western Ireland, and is the largest of the A-A’ . The formation of a shallow marine VE = 17x and Geomorphology 43 A-A’ environment during the Carbonifereous Period S A’ B’ H (358.9 Ma) resulted in the deposition of 66 Figure 3. Shore-parallel profiles (G-G’, H-H’, I-I’) show biogenic carbonate sediments which eventually 0 2705 H’ with glacio-karst features, shown by the brackets. B-B’ I would form what is now known as the Boireann B-B’ A B (m) Depth S Map at right shows profile locations. (Burren) – the roughly 360 km2 limestone area 47 S Tilted limestone beds (TL) show terracing, and pitting N North Study Area may be continued dissolution of clints, generating extending from Kilnaboy and Corranroo Bay in I’ large grykes (C&G). the east to the Aran Islands in the west 63 0 Distance (m) 2346 (Geology of the Aran Islands)(Fig. 7). During the TL 40 - G-G’ Pleistocene Epoch, decreased global C-C’ TL C&G 53 Southwest Study Area temperatures caused eustatic sea level drop and C 60 - glaciation to the islands, which resulted in the D 0 3300 84 smoothing of the exposed limestone (Fig. 5) 0 2760 C&G C&G (McNamara, 2009). The landscape of the islands 45 - H-H’ (m) Depth D-D’ TL are raked in appearance, as erosion from rain C’ 59

H’ water has formed fractured pavement slabs of D’ Depth (m) Depth 70 - smooth limestone (“clints”) with deep cracks 81 0 2728 0 3300 and trenches that separate them (“grykes”) (Fig. Distance (m) VE = 15x 5). The island has a terraced nature from TL erosion and weathering which gives it a ‘stair- E-E’ TL 60 - I-I’ Southeast Study 53 step’ terraced structure from tilting tectonism E Area 72 - 0 3300 and erosion by glacial smoothing. The Aran F 81 islands are unique in their glacio-karstic 0 3458 Distance (m) TL deformation as the major processes of erosion 48 F-F’ F-F’ and geomorphological evolution are dissolution (m) Depth

based from rain water runoff, with glacial E’ 76 METHODS RESULTS deformation less prevalent than karstic F’ • 0 Distance (m) 3154 Data for this research were Shore-Parallel Profiles: deformation. collected using a Kongsberg • Shore-Parallel profiles showcase the grykes and clints The purpose of this study is to further Figure 4. Shore-Normal profiles of Inishmore Island bathymetry in the North (A-A’, B-B’) show sediment- EM2040 multibeam sonar formed from weathering and erosion (Fig. 3, G-G’). characterize the geomorphology of the aboard the R/V Celtic submerged limestone adjacent to the Aran filled channels (S), whereas Southwest (C-C’, D-D’), and Southeast Study Areas (E-E’, -FF’) exhibit terraced, Shore-Normal Profiles: tilted limestone beds (TL). Profile locations are shown at left. Voyager, from 05/26/14 to • Shore-Normal profiles exhibit similar bathymetric Islands. 06/07/14. “stair-step” characteristics as those seen on land (Fig. • Sonar data were post- 3, F-F’). DISCUSSION Figure 5. processed and analyzed (left) Aerial photo of • The weathering of the limestone along fault planes The results of this study reinforce the pre-existing using CARIS HIPS & SIPS 9.1. from subaerial exposure supports the previous smoothed glacio- • geomorphological literature of the area based on profiles and karst island of A 2m resolution CUBE BASE literature on the rise and fall of sea level during this surface and profiles of the bathymetric data (Fig. 3, 4, 6). The bathymetry of the site was Inishmore, Ireland time leading to the deposition and subsequent erosion similar to the topography of the island in the systems of clints (Google Photos). J’ major geomorphological of the limestone. features were made for and grykes found in the limestone from various weathering GRYKES CLINTS events that have occurred since the Pleistocene. Overall, the (right) Clints analysis. Inishmore Cross-Island Profile: (limestone slabs) • Limestone deformation • A cross-island profile (Fig. 8, J-J’) showed a relatively offshore bathymetry appears to be a continuation of the and grykes (crack consistent with this region’s flatter topography to the bathymetric profile (F-F’) landscape of the islands. separation) on geologic past was observed which we attribute to long-term subaerial exposure Ultimately, the results of research on the Aran Islands could be Inishmore Island using the tools in HIPS and and erosion of Inishmore since well before the beneficial in understanding the characteristics of glacio-karstic (Google Photos). SIPS 9.1 Pleistocene. limestones across the globe.

140 REFERENCES J J’ N • Cuan Na Gallaimhe INFOMAR | Galway ACKNOWLEDGEMENTS

We would like to thank CARIS for ) Bay, http://www.infomar.ie/surveying/ GALWAY their Academic Partnership, the J Bays/Galway.php (accessed February 2017). Inishmore Topography Limestone of Department of Geology & Environmental Geosciences, The • Here, C., Visit, T.O., and Islands, A. Inis Mór Elevation (m Elevation (elevation above sea level) J’ College of Charleston BEAMS F (Inishmore ): Inis Mór (Inishmore) Aran Islands - Program, GSI & the INFOMAR project, The R/V Celtic Voyager, and Galway - , ttp://www.aranislands.ie/inis-mor- BEAMers Robert “RJ” Kozich III, and 0 F’ inishmore/ (accessed February 2017). Luke Hollahan. 0 Distance (m) 4000 0 F Bathymetry South of Inishmore F’ • Islands, T.A. Geology of the Aran Islands: Figure 6. Cross-Island elevation profile J-J’ (above) made from a Google • McNamara, M.E., 2009, The geology of the Burren topographic map of Inishmore (upper right) is shown at the same scale as (depth below sea level) Region, Co. Clare, Ireland: Report, p. 66pp, Shore-Normal profile F-F’ (right) to illustrate the similarity in slope from the Figure 7. Geologic map of the Boireann (Burren) region of

top of Inishmore to a depth of over 75 m (VE=17x). Profile locations are (m) Depth http://www.burrengeopark.ie/wp- western Ireland near to Galway, highlighting the Limestone shown on the map. Note that the bathymetry’s spatial resolution is far content/uploads/2013/04/Burren_ substrate of the area (light blue). Map courtesy of the greater than the topography’s, and features are more detailed. 76 Geological Society of Ireland. Geoscientific_Guide_NEED.pdf. 0 Distance (m) 3154