Wednesday, November 22, 2006

A volcanic eruption in Iceland is linked to a famine in Egypt

Nile delta
Agricultural productivity in the Nile valley depends on the river's annual floods. A volcanic eruption in Iceland disrupted that cycle in 1783 and 1784. Credit: Multi-Angle Imaging Spectroradiometer (NASA/GSFC/JPL, Jan. 30, 2001).
A news item in Science Daily vividly demonstrates the global interconnectedness of environmental events.

In June 1783, Iceland's Laki volcano began a series of eruptions. These are believed to have been the largest high-latitude eruptions in the last 1,000 years. Laki expelled three cubic miles of lava and more than 100 million tons of SO2 and toxic gases.

The summer of 1783 was the coldest in 500 years in some parts of the northern hemisphere. Northern Africa received a particularly harsh blow. Drought gripped northern Africa and restricted the flow of the Nile. The unusually cold weather also weakened the monsoon season in southern Asia and northern Africa. In 1783 and 1784, the Nile did not fully flood its banks. No rain, no floods, no crops, no food.

Featured articleLuke Oman, Alan Robock, Georgiy L. Stenchikov & Thorvaldur Thordarson, High-latitude eruptions cast shadow over the African monsoon and the flow of the Nile, 33 Geophysical Research Letters, L18711, doi:10.1029/2006GL027665, 2006:

Nile floodplainNile River records indicate very low flow following the 1783–1784 Laki volcanic eruption, as well as after other high-latitude volcanic eruptions. As shown by climate model simulations of the Laki eruption, significant cooling (−1° to −3°C) of the Northern Hemisphere land masses during the boreal summer of 1783 resulted in a strong dynamical effect of weakening the African and Indian monsoon circulations, with precipitation anomalies of −1 to −3 mm/day over the Sahel of Africa, thus producing the low Nile flow. Future high-latitude eruptions would significantly impact the food and water supplies in these areas. Using observations of the flow of the Nile River, this new understanding is used to support a date of 939 for the beginning of the eruption of the Eldgjá volcano in Iceland, the largest high-latitude eruption of the past 1500 years.

Received 24 July 2006; accepted 24 August 2006; published 30 September 2006.

Index Terms: 1812 Hydrology: Drought; 3311 Atmospheric Processes: Clouds and aerosols; 3354 Atmospheric Processes: Precipitation (1854); 8409 Volcanology: Atmospheric effects (0370); 1605 Global Change: Abrupt/rapid climate change (4901, 8408).

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