A visit during the majority of the year will show a Congress Pool that appears pale blue in color, as seen in the picture on the left. Due to the variable nature of Norris features, it is possible to see the same pool looking muddy and boiling violently as pictured to the right.
At Norris, geothermal "disturbances" take place annually. No other thermal area in Yellowstone exhibits this phenomenon. Mysteriously, features throughout the Norris area undergo dramatic behavioral changes, literally overnight. Clear pools become muddy and boil violently, and some temporarily become geysers. These disturbances often occur in late summer and early fall but have been observed throughout the year.
Features that typically behave as geysers may display altered eruption cycles or temporarily cease erupting. New features may be created during a disturbance, although they seldom remain long-term attractions at the basin. Disturbances tend to last from a few days to more than a week. Gradually, most features revert to "normal" activity.
Why this happens is not fully understood. Further study will no doubt yield new clues that will help unravel the mystery of this phenomenon and lead to a greater understanding of the earth's hidden geologic forces.