Yellowstone Lake Sediments Reveal 15,000 Years of Drought, Fire and Geyser History

A study led by Montana State University geoscientist Cathy Whitlock has reconstructed 15,000 years of vegetation, wildfire and hydrothermal activity in Yellowstone National Park's Lower Geyser Basin, the park's largest thermal area. The findings were published in the Proceedings of the National Academy of Sciences.

The team, which included researchers from the U.S. Geological Survey, Oregon State University, Manchester University and Colorado State University, drilled sediment cores from small, closed lakes in the basin — lakes with no inflowing or outflowing streams that likely formed in craters left by hydrothermal explosions during past wet periods. Pollen in the sediment layers revealed the vegetation present at different times, charcoal marked past wildfires, and the concentration of arsenic, cesium and diatom composition tracked changes in hydrothermal activity and lake chemistry.

After glaciers retreated from the region, a grassy steppe gave way to lodgepole pine forest between roughly 12,800 and 11,000 years ago, and that forest has changed little since despite shifting climate — a persistence Whitlock attributes to the plateau's nutrient-poor volcanic soils and the pine's adaptation to fire. Fire activity, however, responded strongly to climate. Comparing the lake records with high-resolution paleoclimate models showed that summers between 12,000 and 6,000 years ago were warmer and drier than today's, matching charcoal evidence of more frequent fires and diatom evidence of lower lake levels during that period.

Whitlock's team began developing its charcoal-analysis techniques after the major Yellowstone fires of 1988, tracking how far charcoal particles traveled and how long they took to settle into lake mud. Those methods are now used in fire-history studies on every continent.