Contents

• Introduction
• Description
• Other slides
• Factors
• Potential
• Action
• Summary
• References
• Appendix A
• Appendix B
• Appendix C
• Plate 1

The April 1996 Rockland Landslide

Appendix A: Photographs of 1996 Landslide Site

	Figure A1. Airphotos of northern shore of Rockland Harbor prior to 16 April, 1996 landslide. (a) 5/3/66 (photo by J. W. Sewall Company) showing old Samoset Resort; (b) 9/4/87 (photo by J. T. Kelley); (c) 11/94 (photo by J. T. Kelley). Photos (b) and (c) show progress of work along access road to new Samoset Resort.
	Figure A2. The Gerrish house several days after slide. Pavement of Samoset Street is visible in extreme lower right. Typical arcuate head scarp of the slide cuts across lawn and driveway of the Gerrish house. The first major failure involved land behind the house. The second major failure destroyed the Gerrishs' garage and portion of their house.
	Figure A3. View to northwest across slide toward the Gerrish house showing the vertical head scarp. Natural horizontal layering of marine clay can be seen at left of house indicating that this area has very little fill over the marine clay. Roof of Smalley house in foreground.
	Figure A4. View to the southeast across slide to the Smalley property showing rotational slide blocks mantled with a carpet of turf. Typical scarpward tilting of slide blocks is evident in the slab of driveway pavement just to left of and below lamp post.
	Figure A5. View to southeast from behind the Gerrish house of the arcuate head scarp of slide. Behind trees in center of picture is the curved toe of the slide extending 450 feet (140 meters) onto adjacent mudflat.
	Figure A6. In foreground are clay blocks which have spalled off the head scarp. Spalling is facilitated by vertical fractures in the upper part of the marine clay which form the offset vertical surfaces in the scarp behind the fallen blocks. Manganese staining of the fractures indicates that ground water had been flowing through the fractures for some time.
	Figure A7. View across the widest section of slide showing destruction of buildings that collapsed into the slide. Before the landslide, most of this area was backyard lawn.
	Figure A8. View to the northeast from the intertidal mud flat. This photograph shows clay blocks in the toe of the slide. The damaged Gerrish house is visible in upper left and the Smalley house site is visible in upper right. The extreme toe of the slide contains sediments which originally were at the wave-cut base of the bluff.
	Figure A9. View from the Gerrish backyard of the toe of the slide showing several slide blocks with their tops rotated landward toward the head scarp. This is particularly apparent in the block topped with turf in left center and the group of poplar trees just above it. Rainwater has pooled in the depressions between blocks.
	Figure A10. View toward the north showing the toe of the slide. Most trees in the slide show backward rotation toward the head scarp but several in this photo and elsewhere are vertical or at different orientations. This may be indicative of flow rather than simple block rotation as the mode of failure in some parts of the slide. Geologists in foreground survey the perimeter of the slide.
	Figure A11. Close-up of a rotated block composed of fractured marine clay. Unlike the 1973 slide, few blocks remained intact in the 1996 slide. Notice grooves in the clay that formed as different blocks slid past each other and around the tree. Cracks formed as the clay dried and shrank.
	Figure A12. View to southeast across the slide. Motion was from left to right. In this photograph, several curved ridges representing individual slide blocks extend from lower foreground across the slide to the far side. Each ridge is a single block of the same material along its length, either soil or turf, but neighboring ridges may be made of different materials. The retrogressive failure did vary the orientation of blocks and trees, but it did not result in the mixing of different layers. The whole area pictured used to be the flat area on top of the bluff that is missing from figure A7. The former slope at the front of the bluff has moved onto the mudflat, to the right of this picture.
	Figure A13. Photograph of arcuate ridges showing their common, subparallel orientation and height of several feet.

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Contents   Introduction   Description   Other slides   Factors   Potential   Action   Summary   References   Appendix A   Appendix B   Appendix C   Plate 1

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Last updated on October 6, 2005

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