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Eruptions
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More than 1,000,000 eruptions have been recorded.
Harry Woodward first described a mathematical relationship between the
duration and
intervals of the eruptions in 1938.
[9][10]Old Faithful is not the tallest or largest geyser in the park; those titles belong to the less predictable Steamboat Geyser.[4] The reliability of Old Faithful can be attributed to the fact that it is not connected to any other thermal features of the
Upper Geyser Basin.
[11]
Eruptions can shoot 3,700 to 8,400 US gallons (14,000 to 32,000 L) of boiling water to a height of 106 to 185 feet (32 to 56 m) lasting from 11⁄2 to 5 minutes. The average height of an eruption is 145 feet (44 m).
[12] Intervals between eruptions can range from 35 to 120 minutes, averaging 66.5 minutes in 1939,
[9] slowly increasing to an average of 90 minutes apart today, which may be the result of
earthquakesaffecting subterranean water levels.
[13] The disruptions have made earlier mathematical relationships inaccurate, but have actually made Old Faithful more predictable in terms of its next eruption.[
citation needed]

Waiting time between eruptions and the duration of the eruption for Old Faithful.
The time between eruptions has a
bimodal distribution, with the mean interval being either 65 or 91 minutes, and is dependent on the length of the prior eruption. Within a margin of error of ±10 minutes, Old Faithful will erupt either 65 minutes after an eruption lasting less than 21⁄2minutes, or 91 minutes after an eruption lasting more than 21⁄2 minutes.[
citation needed]