FAILING GROUND IN TULLY VALLEY, NEW YORK: ARE MORE MUDSLIDE DISASTERS IN STORE?

Mudslides have disrupted proglacial lacustrine units on the west side of Tully Valley in central New YOrk State, and may do so in the future. The latest of several mudslides destroyed 5 houses and yards in 1993; the others were prehistoric. A composite set of rock-block slide slivers cut Devonian sedimentary sandstones and shales on the east side of Bare Mountain above the mudslides. These slivers trap drainage and hold it behind a veneeer of colluvium plastered along their lower flanks. A LIDAR image taken from an aircraft platform in the late 1990s reveals (1) internal structure of the rock-block slivers, and (2) a progression of mudslides from older to younger in a north-to-south direction. Groundwater held within the rock-block slides is hydrologically connected to the Tully Valley brine-contaminated aquifer system, and provides an artesian head to the Valley's proglacial lacustrine units. This head, thus, increases pore pressure while injecting brines to springs along the Valley's western flank at the base of Bare Mountain's eastern slope, both conditions for triggering new mudslides. Progression of mudsliding from north to south through time suggests that the next mudslide will occur adjacent to the south side of the latest where springs release their waters to the back yards of a row of houses that were neighbors to those destroyed in 1993.