Changing Orientation of Ocean-Facing Bluffs on a Transgressive Coast,Cape Cod, Massachusetts

Erosion of the 24 km-long escarpment cut into the unconsolidated Pleistocene glacial deposits of outer Cape Cod, Massachusetts, by wave action during the Holocene transgression has supplied sediment for construction of spits and barrier beaches to its north and south. The major escarpment landforms produced by the erosion are steep coastal bluffs (upper c. 20 m), beaches, and a more gently sloping shoreface (to a depth of c. 10 m). Using differential GPS methods supplemented with LIDAR data we have re-surveyed the bluff portion of the escarpment along cross-shore transects originally surveyed in 1887–1889. Comparison of the surveys indicates that the bluffs erode at an overall century-scale rate of c. 0.8 m/yr, and that the erosion rate increases alongshore north-to-south by a factor of two. We suggest that the resulting change in coastal orientation results from relative sea level rise over the outer continental shelf and associated increase in wave energy from the southeast.