Old Faithful, like clockwork
Old Faithful, a geothermal cone geyser, got its name from an 1870 expedition exploring and mapping the area around what we today call Yellowstone National Park. It erups every 44 to 125 minutes. In 1939, eruptions came an average of every 66 1/2 minutes; today they are an average of 90 minutes apart. 20041011 Lawrence I. Charters