When I say "Yellowstone Park," what's the first thing that comes into your mind? If you're normal, I believe it would be "Old Faithful." If you're of Mr. Hawthorne's ilk, then it would be "Yogi and Boo Boo." But that was Jellystone Park. Extra points if you know the name of the ranger.* This sign was at the entrance to the Old Faithful area. It reads, from the top: Old Faithful's Plumbing Old Faithful's steaming and spouting merely hint at the thermal action below ground. After an eruption, the partially emptied geyser chambers again fill with hot water. As steam bubbles rise, they clog narrow sections of the geyser tube. Pressure and temperature then increase until steam abruptly forces its way upward, discharging some water in preliminary splashing. This splashing apparently unloads enough water to start a chain reaction deep within the system. As larger quantities of water flash into steam, the geyser surges into full eruption. When the geyser tubes are nearly empty, eruption ceases. The system then begins to refill, and the entire cycle starts anew. Predicting Old Faithful Every geyser has its own unique eruption indicators. Between spoutings, watch Old Faithful for signs of impending thermal activity. For most of the interval, steam gently billows from Old Faithful's cone. A few minutes before an eruption, intermittent jets of spray spurt a few feet above the surface. When the spurts become sustained and surge upward, a full eruption has begun. The average interval between Old Faithful's eruptions is growing longer. Frequent earthquakes in and near Yellowstone may alter the underground plumbing, changing the routes of circulating water. Vandalism -- people throwing objects into Old Faithful's vent -- may also contribute to the slowdown. No two eruptions are the same; the height and duration vary. Because the duration of Old Faithful's last eruption determines the time between eruptions, only the next discharge can be predicted. Subsequent eruptions are impossible to predict. Some facts about Old Faithful: Old Faithful, by the way, isn't as faithful as it sounds. The name itself is a bit deceiving. Old Faithful does not erupt every hour on the hour. It is neither the biggest nor the most regular geyser in the park, but 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 and, because of this close observation, Park Rangers are able to predict its eruptions fairly accurately. The interval between eruptions is predicted by noting the duration of the current eruption. The longer the current eruption, the longer the time until the next eruption. Old Faithful's eruption duration, height, and interval between eruptions varies daily. As of January 2010, the eruptions last 1 1/2 to 5 minutes and the average interval between eruptions is 90 minutes. Old Faithful's height ranges from 106 feet to more than 180 feet, averaging 130 feet. 3700 to 4800 gallons of water are expelled during each eruption, depending on the length of eruption. Just prior to eruption, water temperature at the vent is 204 degrees. We arrived in the geyser area at 3:36. The earlier eruption of the other, smaller, geyser was from 3:38 to 3:42. The time stamps for Old Faithful were from 3:48 to 3:52. Pretty good timing. I shot the still photographs of Old Faithful. Mr. Hawthorne was kind enough to shoot the videos for me.