Travel Reference
In-Depth Information
eruption. “Most people photograph this first display,” wrote Mr. Haynes, “and are changing
film about the time the geyser attains its maximum height.”
For the next eruption time, call (307) 344-2751. See
page 359
for Yellowstone webcams to
watch from home.
How Faithful Is Old Faithful?
Old Faithful has
never
in recorded time erupted “every hour on the hour” as you may have
heard. Here are some figures given for average expected intervals between eruptions: 60 to
65 minutes (1870), 65.5 minutes (1964), 78 minutes (1990). The mean interval has recently
varied from a high of 93 to a low of 88 minutes. The range of possible intervals has always
been from about 30 to 105 minutes.
Seismic activity
can
affect Old Faithful. Following the strong earthquake at Borah Peak,
Idaho, in 1983, the average interval between eruptions became greater, at least for a while.
Geoscientists suspect that the geyser may someday seal itself off: a probe sent down its con-
duit a few years ago revealed a very narrow throat about 22 feet (6.5 m) down, and there's
another constriction about 70 feet (21 m) down. Silica may continue building up there, but
how fast is anybody's guess. On the other hand, the geyser's water may actually be eroding
away the narrow section. No one knows for sure.
In recent years, there's been a rumor that the geyser is losing its power or becoming
less regular or much less frequent. The truth is that the average interval between eruptions
has lengthened by a few minutes, but the average height has remained about the same for
more than 140 years.
Some statistics:
• Old Faithful Geyser's height: 106-184 feet (32-56 m), averaging 145 feet (44 m)
• Eruption length: 1.5-5 minutes
• Elevation at Old Faithful: 7,367 feet (2,245 m)
• Boiling point of water at this elevation: 198°F (93°C)
Predicting Old Faithful's Eruptions
Ask a geyser gazer the rule for predicting Old Faithful's eruptions on a summer day and
you would hear: If there is a big crowd around the benches, the eruption will occur within
about 15 or 20 minutes. A more precise prediction method involves timing the duration
of an eruption from the first heavy surge of geyser water through the last splashes of water
above the cone. The longer an eruption lasts, the longer the interval to the next eruption.
