A LONG-TERM PERSPECTIVE ON TROPICAL STORM IRENE AND THE OCCURRENCE OF EXTREME GEOMORPHIC EVENTS BASED ON FLOOD-INDUCED DEPOSITS IN AMHERST LAKE, VT

Large magnitude floods and extreme geomorphic events are by their very nature infrequent events. Nonetheless, the potential for significant damage to property and infrastructure as well as the threat to human lives associated with these events underscores the importance of understanding the factors which influence their occurrence and frequency. Historical records are typically inadequate for accurately constraining the recurrence interval or identifying trends in the occurrence of extreme events. In contrast, natural geologic archives extending beyond the historical period can provide important constraints on the occurrence of extreme events in the past. Natural archives are in turn limited by uncertainties in the origin and significance of the signal preserved in the archive. In late summer of 2011 Tropical Storm Irene passed through the New England region causing widespread flooding and geomorphic change in the form of stream channel and hill slope-erosion. Elevated river discharges and sediment mobilization led to the deposition of flood induced deposits in downstream sedimentary basins. The Tropical Storm Irene event deposit thus provides a valuable opportunity to examine the sedimentary signature of an extreme event of known magnitude as a means for constraining the interpretation of event deposits of unknown origin. We collected sediment cores from Amherst Lake, VT a lake known to be sensitive to flood deposition from the Black River. In Amherst Lake, the Irene event deposit along with heretofore unidentified event deposits from the 1900s distinguishes the 20^th century as a period of anomalous deposition relative to at least the prior millennium. Ongoing core analyses should extend this comparison into the mid-Holocene.