Though it’s neither the tallest nor even the most predictable geyser in the park, Old Faithful is the poster child for Yellowstone and a consistent crowd-pleaser. Every 90 minutes or so the geyser spouts some 8000 gallons (150 bathtubs) of water up to 180ft in the air. It’s worth viewing the eruption from several locations – the geyser-side seats, the upper-floor balcony of the Old Faithful Inn and (highly recommended) from a distance on Observation Hill.
For over 75 years the geyser faithfully erupted every hour or so – one reason for the name the Washburn expedition gave it in 1870. The average time between shows these days is 90 minutes and getting longer, though this has historically varied between 45 and 110 minutes. The average eruption lasts around four minutes. The water temperature is normally 204°F (95°C) and the steam is about 350°F (176°C). The longer the eruption, the longer the recovery time. Rangers correctly predict eruptions to within 10 minutes about 90% of the time. And no, Old Faithful has never erupted on the hour.
A fairly reliable method of calculating exactly when an eruption of Old Faithful is imminent is to count the number of people seated around the geyser – the number of tourists is inversely proportional to the amount of time left until the next eruption.
If you find yourself twiddling your thumbs waiting for the old salt, pause to consider the power of recycling – you are sitting on a boardwalk made from around three million recycled plastic water jugs.