Travel Reference
In-Depth Information
Turn east toward the river at Spa Geyser to see the most gracefully situated and aesthetically
satisfying geyser eruption in the park.
Riverside Geyser**
has been for a century the park's
most regular geyser. A 1909 guidebook stated that it erupted every eight hours for about 15
minutes. Now erupting about every six hours, it is predictable to within half an hour. The vis-
itor center posts predicted times for all predictable geysers.
Riverside Geyser's spray creates a rainbow in the sunlight.
During its eruption, Riverside ejects water from several vents in its chairlike formation on
the far side of the Firehole. Water overflowing the edges of the formation indicates that it will
erupt within an hour or so, while water beginning to spout from the highest hole at the left
means the eruption will occur in about half an hour. The first few minutes of the eruption are
the most spectacular, with water arching over the river up to 75 feet (23 m) from the cone.
The eruption continues for about 20 minutes. Some eruptions spread a veritable curtain of
droplets out over the river.
Back on the main walkway
On the far side of the bridge are two geysers so closely related that they are always mentioned
together and are effectively one geyser.
Fan Geyser's
eruptions come from 10 or 11 vents,
some with water spouting 125 feet (38 m) and over the trail. One vent even jets water
down-
ward
toward the Firehole.
Mortar Geyser,
whose name may come from the cannon-like