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Scientific Investigations Report 2009–5134

Prepared in cooperation with Onondaga Lake Partnership and
Onondaga Environmental Institute

Dendrogeomorphic Assessment of the Rattlesnake Gulf Landslide in the Tully Valley, Onondaga County, New York

By Kathryn Tamulonis1 and William Kappel2

1Cornell University
2U.S. Geological Survey

ABSTRACT

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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.

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U.S. Geological Survey
New York Water Science Center
425 Jordan Road
Troy, NY 12180
(518)285-5600

http://ny.water.usgs.gov

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Suggested citation:

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.



Contents

Abstract

Introduction

Physiography of the Tully Valley

Rattlesnake Gulf Landslide

Tree Sampling and Data Collection

Landslide Movement at Rattlesnake Gulf at the Split-Tree Creepmeter Site

Methods

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

Summary

References Cited



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