Yellowstone is truly a land of fire and ice. The geology of Yellowstone is a study in the dynamic forces of nature. As a result, the current landscape is just the most recent chapter in a book whose pages are being turned daily.
hot spot & volcanism
In the very middle of Yellowstone National Park, a large chamber of molten hot magma sits so close to the surface of the earth that it heats the entire Yellowstone Plateau and provides heat for the geothermal features that are part of the wonder and awe of Yellowstone. It is so large that it went unnoticed for over a hundred years. This dynamic "hot spot" expands and contracts and, in so doing, raises and lowers the region by measurable amounts each year. Over geologic time, it has erupted multiple times and the last eruption left behind a volcanic caldera about 20 by 30 miles in size. It will probably erupt again in the near geologic future.
glaciers & landscaping
Between past eruptions of this supervolcano, Yellowstone's landscape was covered by the ice of many glaciers. Consequently, glaciers modified the volcanic landforms as they ground across them. Mountain tops were carved off. Glaciers and their outwash determined the drainage patterns of the major rivers within the park. In addition, many of the rocks and boulders found in the northern areas of Yellowstone dropped from the ice. And, as the ice passed over the geothermal areas, rocks and debris dropped out to create new hills.
Yellowstone Geyser Basins
The simple essence of Yellowstone is captured in its many hot springs, geysers, steam vents, and mud pots. While these steaming features are found throughout the park, geyser basins have concentrations of them. Certainly, a walk around their boardwalks is well worth the effort as each geyser basin and each feature in them is unique. Along the Firehole River alone, there are enough geothermal wonders to capture your attention for at least a week!
Straddling both sides of the Firehole River, this basin is home to Old Faithful Geyser, Beehive Geyser, Grand Geyser, and many others! You can spend an entire day here alone. But before heading out, check on current predictions for the larger geysers at the Old Faithful Visitor Education Center.
Black Sand Basin
Accessible from the boardwalks near Old Faithful or by driving just north of the village, this basin has several large, colorful hot springs. In addition, Cliff Geyser plays regularly from the banks of Iron Spring Creek.
Named for biscuit-like geyser deposits that have since been shaken loose by the 1959 Hebgen Lake Earthquake, this basin includes several smaller geysers and beautiful pools. Peer into the deep blue waters of Sapphire Pool and watch for Jewel Geyser as it plays frequently in most years.
Midway Geyser Basin
Because the largest hot spring in the park, Grand Prismatic Spring, is here, this basin is very popular in the summer months. You can also peer into Excelsior Geyser's crater and wonder at the large volume of hot water it discharges into the Firehole River. We recommend visiting early or late in the day.
The well-known Fountain Paint Pots trail is located here. Along that trail, Clepsydra Geyser erupts almost continuously. Take a side trip down Firehole Lake Drive to see if you can catch Great Fountain or White Dome Geysers.
Norris Geyser Basin
If you are looking for a longer walk and an other-worldly experience, this is your basin. Norris's Back Basin is home to the tallest, active geyser in the world - Steamboat Geyser! The Porcelain Basin is full of colorful springs and a few unpredictable geysers as well. Norris is the hottest, most active basin in the park - perhaps because it sits atop three fault lines!
For a gorgeous view of Yellowstone Lake, stop and walk around at West Thumb. You can peer into the depths of Abyss Pool and Black Pool, watch the lake water splash around Fishing Cone, and even see some mud pots in this basin. Do watch out for elk and bison as they are frequent visitors to this basin.
Flowing up through limestone, the terraced springs at Mammoth are different from features found in the geyser basins. You won't find any geysers here. However, this colorful hillside is well worth the walk. You can also drive the Upper Terrace Drive for a less strenuous view of similar features.