Scientific Investigations Report 2009–5134
2U.S. Geological Survey
Dendrogeomorphic techniques were used to assess soil movement within the Rattlesnake Gulf landslide in the Tully Valley of central New York during the last century. This landslide is a postglacial, slow-moving earth slide that covers 23 acres and consists primarily of rotated, laminated, glaciolacustrine silt and clay. Sixty-two increment cores were obtained from 30 hemlock (Tsuga canadensis) trees across the active part of the landslide and from 3 control sites to interpret the soil-displacement history. Annual growth rings were measured and reaction wood was identified to indicate years in which ring growth changed from concentric to eccentric, on the premise that soil movement triggered compensatory growth in displaced trees. These data provided a basis for an “event index” to identify years of landslide activity over the 108 years of record represented by the oldest trees. Event-index values and total annual precipitation increased during this time, but years with sudden event-index increases did not necessarily correspond to years with above-average precipitation. Multiple-regression and residual-values analyses indicated a possible correlation between precipitation and movement within the landslide and a possible cyclic (decades-long) tree-ring response to displacement within the landslide area from the toe upward to, and possibly beyond, previously formed landslide features. The soil movement is triggered by a sequence of factors that include (1) periods of several months with below-average precipitation followed by persistent above-average precipitation, (2) the attendant increase in streamflow, which erodes the landslide toe and results in an upslope propagation of slumping, and (3) the harvesting of mature trees within this landslide during the last century and continuing to the present.
For additional information contact:
Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.
Tamulonis, K.L., and Kappel, W.M., 2009, Dendrogeomorphic assessment of the Rattlesnake Gulf landslide in the Tully Valley, Onondaga County, New York: U.S. Geological Survey Scientific Investigations Report 2009–5134, 14 p.
Physiography of the Tully Valley
Rattlesnake Gulf Landslide
Tree Sampling and Data Collection
Landslide Movement at Rattlesnake Gulf at the Split-Tree Creepmeter Site
Event-Response Curve and Precipitation Data
Historic Landslide Activity in Relation to Precipitation and Timber Harvesting
Correlation with Short-Term Precipitation Patterns
Three- and Five-Year Moving Averages
Dry Periods Followed by Wet Periods
Long-Term Patterns Related to Precipitation and Timber Harvesting
Gradual Movement within Deep, Unweathered Soil
Deforestation and Timber Harvesting
Geotropism and Reaction Wood