Is it possible that something as insubstantial and transitory as snow could be responsible for large scale vertical movements of Earth's surface and the excavation of deeply incised gorges?
Extensive regions of the southern Rocky Mountains of the Southwestern United States have experienced more than 1.5 km of erosion over the past 10 million years, including the development of deeply incised canyons almost a kilometer deep. And while climate change has been suspected of having a role in the removal of vast volumes of Earth's crust, determining the specific processes responsible for the large scale erosion has proved problematic.
In this month's GSA Today article, John Pelletier of the University of Arizona has identified the likely culprit -- snow.
Pelletier demonstrates that as the global climate system cooled, the fraction of total river discharge derived from snowmelt increased significantly. The result was a huge increase in the magnitude and frequency of highly erosive floods. Snowmelt descending down from heights of 1.5 to 3.0 km swept across the Intermontane basins, removing kilometers of rock and cutting deep gorges into the large, flat-lying basins, while the surrounding mountain peaks were left largely intact.
Pelletier's research, demonstrating that something as fragile as snowflakes could be responsible for the chasms that slice through the Bighorn and adjacent basins, highlights the challenges involved in understanding our finely balanced Earth system.
- Jon D. Pelletier. The impact of snowmelt on the late Cenozoic landscape of the southern Rocky Mountains, USA. GSA Today, 2009; DOI: 10.1130/GSATG44A.1
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