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Geysers of Yellowstone - Old Faithful
  
Old Faithful
was named by the first official expedition to Yellowstone, the Washburn
Expedition of 1870. They were impressed by its size and frequency. Old
Faithful erupts every 35 to 120 minutes for 1 1/2 to 5 minutes. Its
maximum height ranges from 90 to 184 feet.
It is not the biggest or the most regular geyser in Yellowstone but
it is the biggest regular geyser. Furthermore, it has been erupting in
nearly the same fashion throughout the recorded history of the park.
Through the years, it has become one of the most studied geysers. One
result of this close observation is that the Park Rangers are able to
predict its eruptions fairly accurately. This makes Old Faithful geyser
one of the easiest geysers in Yellowstone to see.
Old Faithful is deceiving. The benches around the geyser are over 300
feet from the geyser but with nothing to judge the distance by, I rarely
realize just how big the geyser is until I get further away. Personally,
I like the view from Geyser Hill. As with any geyser, watch the wind
direction or you may only see steam.
Predicting Old Faithful:
The time to the next eruption, the interval, is predicted using
the duration of the current eruption.
The duration is timed from the first heavy
surge which lifts water skyward at the start of the eruption until
the last small splash above the cone at the very end. The
longer the eruption lasts, the longer the interval until the next
eruption. For instance, a 2 minute eruption results in an interval
of about 55 minutes whereas a 4.5 minute eruption results in an
interval of about 90 minutes. See the following table for more
information.
It is not possible to predict more than one eruption in advance.
| Duration |
1.5 min |
2.0 min |
2.5 min |
3.0 min |
3.5 min |
4.0 min |
4.5 min |
5.0 min |
| Interval |
50 min |
57 min |
65 min |
71 min |
76 min |
82 min |
89 min |
95 min |
Common Misconceptions:
- Old Faithful plays on the hour every hour
- This legend dates back to the early history of Yellowstone Park.
Old Faithful has never played every hour on the hour. It is just as
likely to play on the hour as it to play 17 minutes after the hour
or 23 minutes after the hour or ......
- Old Faithful plays hourly
- Old Faithful's intervals range from 35 minutes to 2 hours. You
might see one interval of 60 minutes but it is very unlikely that
you will see two in a row. This misconception seem to date back to
the 1870 Washburn expedition where one of the members reported that
Old Faithful played "nearly hourly". Each day there are usually
between 21 and 23 eruptions so "nearly hourly" is about true if you
look at the average but on an eruption to eruption basis, hourly
eruptions have never been the norm. No geyser, including Old
Faithful, plays at set times and intervals. There is always some
variation.
- Old Faithful is slowing down
- People expecting an hourly eruption are often surprised when
they have to wait through a 90 minute to 2 hour interval. They then
think that Old Faithful is slowing down. Old Faithful still has its
same interval range, 35-120 minutes, that it has always had. In the
last few years, long interval eruptions have been a little more
common than they were a few decades so the yearly average has
increased by a few minutes over what it was a few decades ago but
this change is very small and the range of intervals is still the
same.
- Old Faithful is getting shorter
- Measurements show that Old Faithful is still as tall as it has
ever been, 90-180 feet. There are a number of reasons people may
feel that Old Faithful is getting shorter. They may have seen an
exceptionally tall eruption last time and this time saw a more
ordinary or even a short eruption. The first time they saw an
eruption they may have been more excited and their excitement caused
them to over estimate its height. Or they may have first seen it a
number of years ago when it was possible to get closer to the
geyser. To accommodate the summer crowds, the boardwalk has since
been moved further back from Old Faithful. Many people don't realize
just how far from the geyser the boardwalk is. With nothing to judge
the distance by, most people severely underestimate the height of
Old Faithful. Its not until they get back farther from the geyser
and see the buildings around the geyser that they realize just how
big the geyser is.
- Old Faithful erupted late or early
- It is only possible to make predictions of the time Old Faithful
may erupt. The geyser will erupt when it is ready. Its the
prediction that is early or late not the geyser.
-
What to look for:
A joke among some geyser gazers, when asked in the summer by a
park visitor about when Old Faithful will next erupt, is to ask the
visitor about the "Old Faithful Indicator." Of course, there is no
Old Faithful indicator in the true sense of the idea. What the
geyser gazer is actually referring to is the crowd seated around Old
Faithful. After the eruption everyone leaves. As the predicted time
for the next eruption approaches, the benches begin to fill and
eventually overflow. Thus, by looking at the crowd, you can get a
rough idea as to when the next eruption is predicted.
If the indicator is broken, say you are lucky enough to be in the
park when there are no crowds, then you'll have to look at the
geyser. Old Faithful goes through a period of preplay prior to an
eruption. This preplay can last anywhere up to twenty minutes. The
preplay consist of splashing and small jetting which often occurs
every few minutes reaching from 1 to (rarely)20 feet in height. It
often lasts just long enough for some excited visitors to start
taking pictures. The eruption usually starts from what initially
looks like just another preplay jet. Short interval eruptions
occasionally start with the first splash seen above the cone but
most require a period of preplay.
Once the eruption starts, the jetting will grow, stop, grow again
and in two or three of these steps, reach maximum height. It takes
10-20 seconds to reach full height. Unfortunately, the full height
is maintained only for a short time. Within a minute, the eruption
starts waning. This is the when you need to pay close attention if
you want to predict the next eruption. The interval to the next
eruption is based on the total duration of the current eruption.
This includes the unimpressive play that ends the eruption. The main
visible difference between a long and short eruption is the duration
of the end play. In a short duration eruption the end play stops
quickly. In a long duration eruption you may see up to 4 minutes of
unimpressive, 5 feet tall, end play. It just doesn't seem fair that
a long wait is due to such wimpy play.
Images on this site are copyrighted and may not be
used or downloaded without the written permission of Russ Finley
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