Blue sky view, to green pine trees and Firehole River, Marathon Pool lying grey sinter plain, Upper Geyser Basin, Yellowstone

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The circular Marathon Pool lies some 21 m (70 ft) from the Firehole River (in the background of the shot). The pool is 3m (10 ft) in diameter. The clear, greenish-blue water is warm rather than hot, so it is edged by orange cyanobacteria. The pool, on rare occasions, erupts a few centimetres below the rim of the pool. Its eruptions are connected to those of the nearby Grotto Geyser.

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Size: 4018px × 2614px
Location: Marathon Pool, between Giant and Morning Glory Groups, Upper Geyser Basin, Yellowstone Hotspot, USA
Photo credit: © robert harrison / Alamy / Afripics
License: Licensed
Model Released: No

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