10 000 yr record of extreme hydrologic events

Abstract

Well-dated lacustrine sediments provide a hydrologic record indicating that the frequency and magnitude of runoff events, and by inference, storms, have varied over the past 10 k.y. in northern New England. We used five sediment cores and radiocarbon dating to develop a chronology of Holocene hydrologic events for the Ritterbush Pond basin, northern Vermont. Chemical and physical analyses allow us to identify 52 distinct layers of predominately inorganic sediment that represent terrestrially derived material delivered to the pond by runoff events. The thickness of some layers suggests hydrologic events at least equal in size to, and probably much larger than, any storm or flood recorded during nearly 300 yr of written regional history. Layer thickness and frequency and, by analogy, storm size and recurrence, change through the Holocene. The largest events occurred 2620, 6840, and 9440 calibrated ¹⁴C years before present (cal ¹⁴C yr B.P.). The most frequent hydrologic events occurred in three periods: 1750 to 2620, 6330 to 6840, and >8600 cal yr B.P. The recurrence interval of layer deposition during stormy periods averages 130 ± 100 cal yr, whereas the recurrence interval during less stormy periods is longer, 270 ±170 cal yr. The Ritterbush Pond event record illustrates the potential of inorganic lacustrine sediment to serve as a proxy record for estimating paleoflood frequency and deciphering climate change.