In the current issue of Geology, University of Rhode Island geological oceanographers Meng-Yang Lee and Steven Carey; Chang-Hwa Chen and Yoshiyuki Iizuka of the Academia Sinica in Taiwan; and Kuo-Yen Wei of National Taiwan University describe their investigation into the possibility that eruptions from the Toba caldera on the island of Sumatra caused a severe "volcanic winter" and the initiation of a glacial period.
The magnitude of the oldest Toba eruptions had not previously been documented due to the difficulty in recognizing their widespread erupted products in marine sediments. Lee and the team of scientists present new data on the distribution of volcanic ash from the oldest Toba eruption in Ocean Drilling Program cores and piston cores in the South China Sea and Indian Ocean. By using high-resolution litho-, magneto-, and oxygen isotope stratigraphic records, the geologists were able to clarify the correlation between distribution patterns in the cores, refine the age of the layers, and reestimate the eruptive volume of the early eruption of Toba.
The results of their analysis indicate that the glass shards from the first Toba eruption 788,000 years ago were dispersed more than 2000 miles from the source. Fallout from the eruption was deposited from clouds that drifted over both the Indian Ocean and the South China Sea, producing an extensive ash blanket that may have been comparable in size to that of the last Toba eruption 75,000 years ago.
Comparing material from the oldest Toba eruption to that of the youngest, or last, Toba eruption, the scientists were able to draw surprising conclusions. The youngest Toba eruption (75,000 years ago) has been proposed as a triggering mechanism for the onset of large-scale glaciation, which brought the last interglacial stage to its end. The coincidence of the oldest Toba eruption with the transition from a glacial stage to an interglacial stage, however, appears to be an opposite effect.
Although the estimated volume of the oldest Toba eruption is not as large as the youngest Toba, they are both enormous eruptions involving discharges of tremendous amounts of magma. However, the warming trend following the oldest supereruption of the Toba appears to suggest that factors other than volcanism have played more influencing roles in governing glacial to interglacial transitions over the last 3 million years.
The URI Graduate School of Oceanography is one of the country's largest marine science education programs, and one of the world's foremost marine research institutions. Founded in 1961 in Narragansett, RI, GSO serves a community of scientists who are researching the causes of and solutions to such problems as acid rain, harmful algal blooms, global warming, air and water pollution, oil spills, overfishing, and coastal erosion. GSO is home to the Coastal Institute, the Coastal Resources Center, Rhode Island Sea Grant, the Institute for Archaeological Oceanography, and the National Sea Grant Library.