Yellowstone National Park, WY (No. 17)
Shell Spring or Shell Geyser is a depression with built up, rounded, yellow, solidified sinter with a small pool at the center that may be reminiscent of a shell. Hard sinter forms a defined feature area before soft sinter and vegetation begins. Shell Geyser eruptions are cyclical, with an active phase that slowly fills the pool area of the feature, a final long eruption when water is overflowing, then the pool drains and remains quiet for several hours. Cycles can occur over hours to days. High activity prevented conductivity measurements.
Shell Spring has an average temperate of 196.5°F (91.4°C) and an average pH of 8.5.
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