Paleo Slide Set: Polar Ice Cores
Signal of a 1479 A. D. eruption of Mt. St. Helens using data from Fiacco et al. (1993)

Volcanic eruptions evident in the ECM record direct scientists to particular core segments 
for further research. Researchers found a clear signal of a 1479 A. D. eruption of Mt. St. Helens 
(first identified in ash deposits in the Pacific Northwest and dated using tree rings) in both the particulate 
(dust) and sulfate (SO42-) records. As you can see from this photo of Mt. St. Helens' 1980 eruption, explosive 
volcanoes (as opposed to shield volcanoes like those in the Hawaiian Islands) hurtle vast quantities of ash 
high into the atmosphere. Just as ash from the 1980 eruption was deposited thousands of miles from the volcano, 
ash from the 1479 eruption was rapidly carried all the way to the Greenland Ice Sheet--probably in less than a 
week--leaving the particulate layer evident in the graph. Why doesn't the sulfate peak coincide with the 
particulate peak? In powerful eruptions like these, the volcano's plume of ash and gases may extend several 
miles into the sky, piercing the stratosphere. Sulfate aerosols in the plume are extremely light and take 
several months (and in the case of eruptions like Mt. Pinatubo in 1991, several years) to precipitate. 
GISP2 researchers estimate that the peak in sulfate deposition occurred 3-5 months after the eruption. 
That environmental events so far in the past can be identified with such clarity demonstrates why scientists 
go literally to the ends of the earth to extract ice cores. 

Photo Credits:
Thomas Andrews 
NOAA Paleoclimatology Program