"Norris Pool" is the very unofficial name given to the geyser across the trail from Fan and Mortar Geysers. The name is derived from a strong acid smell that the feature possesed in the 1980s and early 1990s. This smell is characteristic of primarily acid, Norris Geyser Basin.
While thermal features have been known in this location in the past, for almost two decades prior to 1995, this area looked like nothing more than a depression. In sonme parts of the depression, there were even patches of scraggly grass. Then, in late 1995 a muddy pool started to form. It quickly grew into the soupy mudpot that was seen there until September 1998. In the late summer and fall of 1998, the character of Norris Pool changed again. By late September Norris Pool had thickened some and was developing into a nice, highly active, mudpot. Then on October 3, 1998, Norris Pool started erupting as a fountain-type geyser. Early eruptions were very muddy and only reached about a foot over the rim. By the next day, eruptions were reaching several feet over the rim and were washing mud from around the geyser back into the crater. Meanwhile, the water in Spiteful Geyser, located across the road but obviously connected to Norris Pool underground, turned muddy and started erupting regularly, which it hadn't done for months. Subsequent minor eruptions of Lower Mortar Geyser also looked somewhat opaque, indicating a connection with this geyser as well. Interestingly, the water in Fan Geyser remained clear.
As the activity of Norris Pool continued into the Fall of 1998, the geyser eroded accumulated dirt and mud from around its vent revealing the sintered vent of an old hot spring at that location. Also, the water gradually cleared as the mud washed away. By late October, eruption intervals were about 20 to 50 minutes, durations were about 4 to 5 minutes and heights of the bursting play barely reached about 6 feet but on rare occasion reached as much as 10 feet. When it started erupting as a geyser, Norris Pool was about 6'x8', by October 31 it was 12'x16' and at least 7 feet deep. It showed a definite connection to Spiteful Geyser. Spiteful's water level dropped during an eruption of Norris Pool, only to quickly rebound after the eruption had ended. Norris Pool completely emptied after an eruption of Spiteful Geyser and required longer to build to the next eruption than when Spiteful hadn't erupted.
Toward the end of 1998, geyser activity stopped only to resume with renued vigor in August 1999. Some eruptions in the fall of 1999 reached over 15 feet. Larger eruptions of Norris Pool were frequently followed quickly by an eruption of Spiteful Geyser.