Old Faithful Questions & Answers
Q. When does Old Faithful erupt?
A. Basic prediction of Old Faithful is dependent upon the duration of the previous eruption. During visitor center hours, geyser statistics and predictions are maintained by the naturalist staff. People speak of the average time between eruptions. This is misleading. Intervals can range from 60-110 minutes. Visitors can check for posted prediction times in most buildings in the Old Faithful area.
Q. How high does Old Faithful erupt and how long will it last?
A. Old Faithful can vary in height from 106-184 feet (32–56 m) with an average near 130 feet (40 m). This has been the historical range of its recorded height. Eruptions normally last between 1.5 to 5 minutes.
Q. I heard Old Faithful isn't as faithful as it used to be. Is it slowing down?
A. It depends on what you call faithful. The famous geyser currently erupts around 17 times a day and can be predicted with a 90 percent confidence rate within a 10 minute variation. Because of changes in circulation that resulted from the 1959 Hebgen Lake and 1983 Borah Peak earthquakes, as well as other local and smaller earthquakes, the average interval between eruptions has been lengthening during the last several decades. In the past, Old Faithful displayed two eruptive modes: short duration eruptions followed by a short interval, and a long duration eruption followed by a long interval. However, after a local earthquake in 1998, Old Faithful’s eruptions are more often of the long duration, long interval type. If an eruption lasts less than 2.5 minutes then there will be a 60 minute interval. If an eruption lasts more than 2.5 minutes, there will be a 90 minute interval.
Q. How many gallons of water are expelled during an eruption?
A. It depends on the duration of the eruption. Scientists estimate that the amount ranges from 3,700 gallons (for a short duration of 1.5 minutes) to 8,400 gallons (for a longer duration of 4.5 minutes).
Q. How hot is the water in Old Faithful?
A. During an eruption, the water temperature at the vent has been measured at 204°F (95.6°C). The steam temperature has been measured above 350°F!