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Memo to Boulay Jumbo Mountain Landsliding page 5 episode at Muffler Rock and the April, 1997 passage of the MCC longwall face beneath the scarp area, I have examined available aerial photographs of Muffler Rock taken between 1983 and 1997. I concur with Dames & Moores, and Dr. Richard Dunrud's opinion that the landform of Muffler Rock is that of a repeatedly active landslide scarp. Photographs dating from September, 1983 show the Muffler Rock scarp to be relatively stable, with a veneer of grass and some relatively mature evergreen trees. A portion of ground (approximately 1/4 acre) above and south of the main scarp, appears to be surrounded by a minor head scarp, perhaps five feet in maximum height. This settled block suggests that a wedge of ground (soil and bedrock) immediately upslope from the main scarp was in the process of failing in 1983. These artifacts, common to landslide masses, suggest the Muffler Rock landslide had experienced an extended period of relative stability, perhaps spanning several decades. However, a block adjacent to the main scarp was in the process of moving downslope. Aerial photographs dating from November, 1995, show increasing instability of the soil horizon of Muffler Rock. Scree chutes have developed between tree stands. The grass has been disrupted within these chutes, which are now the locus for downslope sliding of small sized rocks and debris. The scarp surrounding the settled block noted in the 1983 photographs appears to have increased in height. July, 1996 photographs show the Muffler Rock main scarp becoming more unstable. The upper third of the western portion of the main scarp is losing its soil veneer and trees. The talus and debris at the foot of the scree chutes is forming into lobes. The final photograph examined, dated July, 1997, shows the majority of the main Muffler Rock scarp to be devoid of trees. The scarp is now largely debris and talus covered. Perhaps 80% of the trees have been removed by the landslide. The western two thirds of the settled block has settled and been decapitated by sliding laterally onto the main scarp. The eastern third of the settled block now contains several head scarps, suggesting that it is extending and sliding laterally towards the main scarp. The debris pile at the toe of the main scarp has overrun several acres of scrub oak. In summary, the occurrence of subsidence may have accelerated the occurrence of this most recent episode of instability of the Muffler Rock scarp. In my opinion it would be impossible to definitively determine whether subsidence as the single factor had triggered this latest episode of mass wasting of Muffler Rock.