The geologists' research couldn't be more timely. "The last big group of storms was – you guessed it – almost 3,000 years ago," says Paul Bierman, co-author of "Millennial-scale storminess variability in the northeastern United States during the Holocene epoch" and UVM professor of geology. With funding from the National Science Foundation, Bierman enlisted a team of students to collect and study core samples from 21 lakes in Vermont and New York's Adirondacks over four years. The regional storm and flood patterns they were able to establish are red flags to emergency planners, who rely on early detection to quickly evacuate people to higher ground when waters rise.
There was no time for warnings, preparations or escape 75 years ago, when record rainfall overflowed rivers and partially submerged several Vermont towns, killing 55 people and destroying $30 million in property. But geologist Anders Noren says the 1927 flood was merely a drop in the bucket compared to earlier – and future – hydrologic hassles. "If this cycle continues, the frequency and severity of intense rainstorms that can cause massive flooding should continue to increase for the next several hundred years," Noren says. The impact of human activity, especially the emission of atmospheric greenhouse gases, could speed up storm cycles, he says.
Noren, who is lead author of the Nature paper, joined Bierman's research team as a graduate student of geology. In a laborious process Noren calls "a wintry dance," he helped to collect sedimentary archives from frozen lakes by hammering 20-foot pieces of 3-inch diameter PVC pipe to the bottom of the lakes and extracting core samples that were later sliced, photographed and painstakingly analyzed.
"In each of the cores we looked for sandy layers of sediment that were washed into the lakes during rainstorm-induced floods," Noren explains. During "nor'easters," cyclones and hurricanes, material stored in upland streams and basin hill slopes is eroded and transported to lake basins. "By getting radiocarbon dates on the organic materials in and around these layers, we were able to determine when floods occurred. Our main conclusions were culled from an analysis of all these lakes' flood chronologies."
Sediment analysis also involved the efforts of scientists at the Quaternary Research Center and Department of Earth and Space Sciences at the University of Washington, Seattle and the Center for Accelerator Mass Spectrometry, Lawrence Livermore National Library, Livermore California. For more information contact Lynda Majarian at 802-656-1107 or lynda.majarian@uvm.edu.
Journal
Nature