Landsat-8 nighttime thermal infrared image from April 2017 showing the Tern Lake

Landsat-8 nighttime thermal infrared image from April 2017 showing the Tern Lake area. In Yellowstone, temperatures are extremely cold at night in the winter, and most lakes are frozen (dark pixels). West Tern Lake seems to be thawing here - perhaps it receives some thermal waters from nearby hot springs. The patch of bright (warm) pixels between West Tern Lake and the Tern Lake thermal area has emerged over the last 20 years. Lakes are outlined in blue; the boundary of the Sour Creek resurgent dome is in black; known thermal areas are outlined in red; and the red triangles are individual thermal features that have been mapped.