Move your cursor over the photo to see the yellow ash markers.
Photo Courtesy of Dr. Mark Shapley

This is one of the core sample sections taken from a small lake between Missoula and Great Falls. The cores, which represent the top 8.85 meters of sediment in this particular lake, are a repository of information about climate, vegetation, and fires over the past 12,500 years for the area. This 90 cm section (4 inches in diameter) consists of mud buried 4.8 to 5.7 meters beneath the lake. Each centimeter of length represents 10-15 years of deposition. This particular core includes ash (tephra) from the eruption of Mt. Mazama 7,600 years ago (between the two yellow lines). Move your cursor over the photo to see the lines.

NOTE: The core has been carefully cut down the middle. Although sediment in some lakes is varved (has distinct annual/seasonal layers), the layers shown here are not varves. Instead, they were caused by other changes in the lake ecosystem, such as algae blooms, changes in climate, or changes in the lake's hydrology.