Subaerial and Subaqueous Investigations of Volcanic Debris Avalanche and Lahar Deposits on the Northern Coast of Ulleung Island, Korea

Abstract

Chun, J.-H. and Lee, H.-J., 2019. Subaerial and subaqueous investigations of volcanic debris avalanche and lahar deposits on the northern coast of Ulleung Island, Korea. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 369-376. Coconut Creek (Florida), ISSN 0749-0208.Volcanic debris avalanche and lahar deposits associated with small-scale lava dome collapse have been poorly documented in volcanic islands. The Chusan Formation was emplaced on the collapsed northern flank of Ulleung Island, Korea. Subaerial and subaqueous investigations of the collapsed northern part of Ulleung Island have been performed based on shaded relief images generated from a digital elevation model (DEM), a GeoEye satellite image, outcrop observations, and multi-beam echosounder and high-resolution Chirp sub-bottom profiling systems. The Chusan Formation is an elongated (length, 800 m; width, 250 m) system of valley-confined deposits connected to the Albong lava dome within the Nari caldera depression. A 40-m-thick outcrop of the Chusan Formation consists of three aggradational units that were emplaced by lahars, volcanic debris avalanches, and mixed deposition due to these processes. The peat layer between the overlying Chusan Formation and underlying reworked sediments was dated at 3,070–3,275 cal B.P., matching the emplacement of the Chusan Formation. Equivalent subaqueous deposits of the Chusan Formation were not detected in the northern shelf; thus, large-scale caldera collapse deposits covered the marine terrace before emplacement of the Chusan Formation. The valley-confined Chusan Formation is the result of an aggradational succession of lahar and volcanic debris avalanche deposits associated with the Albong lava dome collapse, corresponding to the most recent volcanic activity of Ulleung Island.