U.S. Geological Survey Open-File Report 2009-1042
National Assessment of Historical Shoreline Change: A Pilot Study of Historical Coastal Bluff Retreat in the Great Lakes, Erie, Pennsylvania
Figure 2. (A) This low-angle oblique aerial photograph shows a location along the coast of Lake Erie, Pa., where high bluff recession was accurately documented in a Pennsylvania Coastal Resources Management Program monitoring study because the location of the control points along which bluff retreat is measured captured the large landslide. (B) This low-altitude vertical aerial photograph of the same area showing the location of the control point (blue dot) and the azimuth (blue arrow) along which the transects are measured. This is also the area of the highest measured retreat rate (1.0 m/yr) assessed in this pilot study. Photographs from Pennsylvania Coastal Resource Management Program.