Travel Reference
In-Depth Information
less than a mile (1.5 km). Features along this trail are described from its other end on
pages
Biscuit Basin Loop Walk
NOTE:
The first area after the footbridge has been surprisingly active since 2006.
Black Opal Pool
erupted explosively in May 2009, causing geologists who happened to be present to debate
whether it had an especially forceful eruption or a hydrothermal explosion. Late in the 2012
season Black Opal and the next two pools,
Black Diamond
and
Wall,
had merged into one
large pool, at least temporarily.
In the distance near the river is a relatively new perpetual spouter informally called Salt
and Pepper for its early tendency to throw out dark rocks in addition to water.
The once crystal-clear
Sapphire Pool
was delightful to watch. Visitors stood transfixed,
watching a string of bubbles from far below, followed by an overall sizzling, and then a surging
boil that engulfed the whole spring. Then, due to the 1959 Hebgen Lake earthquake, Sapphire
began erupting 125 feet (38 m). These violent eruptions increased the size of Sapphire's crater,
destroyed its unique “biscuits,” and changed its shape from circular to oval. By 1964, the erup-
tions were much smaller, and a few years later it ceased any significant activity.
Take the boardwalk loop to the right beyond Sapphire to see several other features, in-
cluding the deep cavernous vent of
Black Pearl Geyser.
Black Pearl was thickly studded with
quarter-inch black knobs when it was named in the first part of the twentieth century. At the
boardwalk curve is
Mustard Spring,
really two small geysers connected underground.
Avoca Spring
is the grotto-like cone located near Mystic Falls Trailhead. Avoca was a boil-
ing spring until 1959, when it developed into an erratic geyser.
Silver Globe Geyser,
next to Avoca and connected to it, can mesmerize you when it has
silvery white bubbles rising from deep within its clear pool. Here's proof of the erudition of
early Yellowstone namers, especially of tour guide George Henderson: he called the geyserite
arch in and over Silver Globe Geyser the Zygomatic Arch, because it reminded him of a hu-
man cheekbone.
A number of very hot features (including Avoca Spring and others to its south) are
grouped into the
Silver Globe Complex.
Geyser expert T. Scott Bryan has suggested that a
marked increase in activity here beginning in 1983 was linked to an Idaho earthquake of that
year centered 150 miles (240 km) away at Borah Peak (Idaho's highest point).
Starting across from Avoca Spring, the
Mystic Falls Trail
is about 3.5 miles (5.6 km)
round trip, with steep sections near the falls. A left turn at the first junction would lead you
