Two of the largest volcanic eruptions in human history occurred in the Indonesia Islands in the year 1815 and again in 1883. Although these catastrophes claimed thousands of lives and affected the climate on a global scale, they also created a unique opportunity for future scientists. For up to two years following each eruption, the earth's weather washed out the dust and aerosols in the form of sulfuric and nitric acids, leaving behind a chemical "fingerprint" in the rain and snow.
Halfway around the world, 11,000 miles away and 176 years later in 1991, a team of U.S. Geological Survey (USGS) scientists removed an ice core the length of two football fields from Upper Fremont Glacier in the Wind River Range of Wyoming and it contains chemical deposits from these eruptions.
"We have found evidence of the 1815 Tambora and 1883 Krakatau eruptions locked deep within the glacial ice below the glacier's surface," said Paul Schuster, a USGS hydrologist. "This is a remarkable discovery - the first of it's kind from a glacier in the contiguous United States."
Schuster and his colleagues recently moved the achieved ice core to the National Ice Core Lab (NICL) in Denver. Working in the sub-zero (-11 F) laboratory environment for more than a month, they analyzed the chilly remains of these volcanic events using a technique known as Electrical Conductivity Measurement (ECM). Their research is highlighted in the Feb 27 edition of the Journal of Geophysical Research.
Historic volcanic events, along with chemical age dates, are used as time markers to develop a chronology of the ice core. Once an accurate chronology is established, data from the core can be used to reconstruct the time scale of climate changes in the past 250 years. Evidence from this ice core indicates that the Little Ice Age, a period from the 1400's to the mid-1800's characterized by cooler temperatures, took less than 10 years to end (circa 1840-1850).
"This research suggests that major climatic shifts in alpine regions of North America can occur on a 10-year scale," said Schuster. "Based on these findings, it's not unreasonable to consider the possibility that a major shift in climate could occur well within an average human lifespan."
In addition, chemical analysis of the ice core can provide information on the changes of chemical quality of snow falling in the Rocky Mountains over the last 250 years. A chemical profile of snowfall spanning this timeframe provides insight to the man-made effects on precipitation chemistry.
The ice core work is supported in part through an interagency agreement between the USGS and the U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory. Two additional cores were recovered from Fremont Glacier in July 1998 and are currently being analyzed.
No other ice cores of this length, representing more than 250 years of past climate, have been recovered in the lower 48 United States.
"The results from this research greatly increased the resolution (accuracy) of the time line represented by this ice core providing us with unique look at climatic and environmental changes back to the time when our first President was just a child. The information from this study can provide insight to the possibility of future climatic changes that may affect us and our children's children," said Schuster.
As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2000 organizations across the country to provide reliable, impartial scientific information to resource managers, planners and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, to contribute to the conservation and the sound economic and physical development of the nation's natural resources, and to enhance the quality of life by monitoring water, biological, energy, and mineral resources.
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