Yellowstone Geysers and Hot Springs
In Yellowstone National Park there are about 500 geysers and some 10,000 thermal features. Yellowstone contains the majority of the world's known geysers. The geysers and other features are major attractions. Old Faithful geyser is perhaps the park's best know and most visited attraction.
Many lesser-known geysers are equally impressive and can be seen along park roads or at the end of short hikes. Others are located far into the backcountry where they are difficult to reach.
Why are there so many thermal features here? Much of Yellowstone sits inside an ancient volcanic caldera (the exploded crater of a volcano). The last major eruption occurred about 600,000 years ago. For hundreds of thousands of years after that eruption, subsequent lava flows slowly filled in most of the caldera. Even now, in some places, nearly molten rock resides as little as 2-5 miles below the surface. Water percolates down into the caldera and is heated by that volcanic activity. The heated water and steam develops great pressure, forcing it to the surface and producing the park's geysers, hot springs, fumaroles and mudpots.
Many of these thermal features are located in Yellowstone's major geyser basins: Upper, Midway, Lower, Norris, West Thumb, Shoshone and Heart Lake.
Old Faithful was named by the first official expedition to Yellowstone, the Washburn Expedition of 1870. The explorers were impressed by the geyser's size and frequency. Old Faithful erupts every 35 to 120 minutes for 1.5 to 5 minutes. Its height ranges from 90-184 feet.
Old Faithful is not the biggest or the most predictable geyser in Yellowstone, but it is the biggest regular geyser. Through the years, it has been studied intensely and scientists can predict its eruptions fairly accurately. This makes Old Faithful one of the easiest geysers to see erupting.
Old Faithful is located in the Upper Geyser Basin. Relatively few people press beyond Old Faithful and the visitor facilities to see other impressive features nearby. The Upper Basin covers only about one square mile and is home to many geysers and some very pretty hot springs. An extensive series of boardwalks lead through the basin. Visitors are asked to stay on the boardwalks, for their own safety and to protect fragile features.
Interpretive pamphlets about the park's geyser basins can be purchased at visitor centers and at the start of many boardwalks and trails.
The largest predictable geyser in the world is located in the Upper Geyser Basin. It is known as Grand, and it is larger and lasts longer than Old Faithful. It is very spectacular and photogenic. Unfortunately, it cannot be predicted as accurately as Old Faithful so some waiting is required if you want to see it erupt.
Grand Prismatic Spring is the major attraction in Midway Geyser Basin. It is a very colorful spring and pool where water and bacterial mats radiate with a kaleidoscope of colors. The pool measures 250 feet by 380 feet, making it is the largest hot spring in Yellowstone and the third largest in the world.
The Lower Geyser Basin is the largest in the park, covering about 11 square miles. Two roads, Fountain Flat Drive and Firehole Lake Drive, provide access to many geysers and hot springs. A favorite here is known as Great Fountain (eruption predictions are posted at the Old Faithful Visitor Center and at the geyser).
The Norris Geyser Basin is the hottest thermal area in the park. The water here is slightly acidic, whereas the water is slightly alkaline in other areas). Because of this, the features in this basin have a different appearance that at other area in the park.
Impressive Mammoth Hot Springs is located near the park's North Entrance. It includes a large hill of travertine, created over thousands of years as hot water flows from the spring and then cools and deposits its calcium carbonate on the hill.
The West Thumb Geyser Basin is located along part of Yellowstone Lake. Some geysers and hot springs come up under the lake. Other impressive hot pools can be seen near the lake.