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​What Makes Old Faithful So Faithful?

a train on a track with smoke coming out of it

Most geysers are not predictable. But, of course, we all know that the granddaddy of all geysers is one we have been counting on for years. The ability to determine the eruptions of Old Faithful with impressive accuracy is what earned the world’s most famous geyser its name. Many people mistakenly believe that Old Faithful erupts on or near the same time each day. While that may happen, the times of the previous day’s eruptions don’t actually play a role in the predictions the Yellowstone Park Rangers post each morning.

Factors to Consider

Old Faithful eruptions vary in terms of how long they last and how much water is expelled during the eruption. These two factors are related. Longer eruptions spew forth more water. To understand how this impacts the timing of the next eruption, it helps to know a bit about the make up of a cone geyser like Old Faithful.

Cone Geysers

Beneath the surface of a geyser is a reservoir filled with superheated water. This reservoir is connected to the geyser vent by a significantly smaller channel. The expanding superheated water and steam creates high pressure that causes the water to move towards the surface.

As the water moves towards the surface, it cools and loses pressure. Since the small channel leading to the vent constricts the flow of water, pressure begins to build up in the reservoir. Eventually, this superheated water gets hot enough to flash into steam which expands and forces the water in the channel out through the vent.

So How Does This Impact the Eruption Times?

When Old Faithful erupts for longer periods of time, more water is expelled. That means that there is less water remaining in the reservoir. Before the next eruption, the reservoir will have to fill and increase in temperature until it is superheated.

If Old Faithful erupts for a shorter period of time, the water that remains in the reservoir is still pretty hot. Some of it may even be superheated, so the interval after a short eruption is smaller than the interval after a long eruption.

Is There a Formula?

Actually, the National Park Service provides a rule of thumb formula for visitors to follow when visiting Yellowstone. Basically, if the previous eruption lasted for less than 3 minutes, the interval until the next eruption will be approximately 68 minutes. For eruptions that last more than 3 minutes, the interval is about 94 minutes before Old Faithful erupts again.

Park Rangers at Yellowstone track Old Faithful’s eruptions. When making predictions for the day, they take into account the length of and intervals between the most recent eruptions.

If you are interested in predicting geyser eruptions or just want to see Old Faithful do its thing, you will definitely want to include a Scenic Safaris adventure to your Yellowstone visit. Contact us today for information about our Old Faithful Geyser Basin Hike. Our knowledgeable guides can get you to Old Faithful and share other wondrous phenomenon that this amazing National Park has to offer.