Introduction

Lake Superior is one of the largest bodies of freshwater in the world (Johnston, 2012). Its immensity leads to our understanding that lake level in the basin mimics sea level when studying coastal landscapes. During the Late Holocene, several lake level fluctuations have occurred creating a varied suite of coastal landforms. Historic shorelines are preserved in coastal landscapes and wave cut bluffs and cliffs (Fig. 1). Lake Superior coastal landscapes evolve as lake level fluctuate, creating a unique opportunity to study how coastal landforms adapt in response to sea level changes. Sediment inputs cause coastal landforms prograde (build out from shore) (Ritter, et al., 2011). Though progradation during regression (relative sea level fall) is widely accepted, how, or even if, progradation during transgressive (relative sea level rise) occurs is not well understood (McCubbin, 1982). This research seeks to provide insight into the subsurface stratigraphy of the Grand Island Tombolo in order to better understand its continuing formation. In order to achieve our objectives this study used GPR to provide a means of imaging subsurface stratigraphy to establish the depositional style of various radar facies with radar stratigraphic analysis. A GPR transect of the Grand Island Tombolo is interpreted using radar stratigraphic techniques and divided into four radar facies. Radar facies are interpreted as shoreface and strandplain deposits, the contact between which is interpreted as lake level.

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