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September 13, 2020

Yellowstone’s most famous thermal areas, like Norris Geyser Basin, are located on land, but a surprising number of thermal areas are also present beneath the region’s lakes. Thermal satellite data can help to identify and characterize these hidden sources of heat!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from R. Greg Vaughan, research scientist with the U.S. Geological Survey.

Map of thermal areas and lakes in Yellowstone National Park
Map of thermal areas in Yellowstone (red), as well as lakes (outlined in blue), many of which have thermal areas on their shores or beneath their surfaces.

Mapping thermal areas in Yellowstone is a work in progress, not only because some areas are in remote wilderness, but also because changes occur frequently.  Groups of thermal features expand and contract, develop and decay, and migrate, all over time scales that range from weeks to months to years.  The new thermal area that formed over the past 20 years near Tern Lake is a good example.

Thermal areas are also present beneath lakes in Yellowstone.  In fact, one of the hottest thermal areas in the park is beneath Yellowstone Lake!  Other lakes also host thermal areas, and by monitoring the lakes, we can get a sense of the activity of these regions.  This is because the lakes freeze every winter, except where they are receiving heat from nearshore hot springs or underwater vents.

Yellowstone has more than 2000 lakes. There are a handful of large lakes (larger than 1 km2, or about 250 acres, in area), including Yellowstone, Shoshone, Lewis, Heart, and Delusion Lakes.  There are 45 lakes that are medium sized (0.1 to 1 km2, or about 25–250 acres, in area), and the rest are small to very small (down to 80 m2, or 860 ft2, in area), most of which are so small they don’t even have a name.

Among the medium to large lakes, there are more than a dozen that have, or are suspected to have, thermal input from nearshore hot springs or underwater vents.  This is based on evidence from a few high-resolution wintertime satellite images that have been acquired by commercial satellite companies.

High-resolution images of Fern Lake, Yellowstone National Park, from different seasons
High-resolution images of Fern Lake from different seasons.  North is up.  Fern Lake is about 1 km across from east to west.  Red arrows in the winter image point to large zones of open water, indicating either nearshore springs or underwater hydrothermal vents, but there are also many smaller zones of open water that are conspicuous. 

While satellites with thermal infrared instruments can directly sense emitted surface heat, their moderate spatial resolution (pixels that are about 90 meters, or about 100 yards, on a side) limits them to detecting only the largest or hottest thermal areas; they cannot detect small, subtle thermal features or small changes in thermal areas.  High-resolution commercial satellite data do not have thermal infrared capabilities, but their meter- (or yard-) scale pixels enable detection of surface features that are characteristic of small thermal anomalies, such as open water on otherwise frozen lakes during the winter, as has been observed at Fern Lake on the eastern side of Yellowstone Caldera and also occasionally on Yellowstone Lake.  Thus, these high-resolution commercial satellite data could be very useful for detecting areas where there are hitherto unknown thermal features that are too subtle to be detected with moderate-resolution thermal infrared data. 

So, returning to the title question: What can Yellowstone’s warm lakes tell us about thermal features?  The answer is, “A lot – if we have remote sensing images that are acquired (1) with a spatial resolution high enough to see meter- (or yard-) scale variations in ice cover, and (2) frequently enough to see seasonal changes in ice cover.”

Currently, there are limited high-resolution data available for searching Yellowstone’s lakes for evidence of unmapped thermal features.  In the future, we hope to partner with commercial satellite companies to use their high-resolution satellite data, combined with NASA’s moderate-resolution thermal infrared data, to develop a better understanding of where Yellowstone’s thermal features are located, how they change with time, and how they contribute to the total heat budget of the hydrothermal system.

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