The largest thermal area in Yellowstone National Park: Lower Geyser Basin
Yellowstone is a land of superlatives. Even in such an environment, the Lower Geyser Basin stands out as one of the most spectacular areas in the park.
Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Michael Poland, geophysicist with the U.S. Geological Survey and Scientist-in-Charge of the Yellowstone Volcano Observatory.
There are a lot of thermal features, like geysers, hot springs, and mudpots, in Yellowstone National Park—well over 10,000. The vast majority of these features are clustered into about 120 distinct thermal areas, which are defined as nearly continuous geologic units that contain multiple thermal features, hydrothermally altered rocks, and heated ground. There may also be gas emissions, and the areas are generally barren of vegetation or have stressed/dying vegetation.
With a size of about 15.6 square kilometers (3,855 acres), Lower Geyser Basin is the largest thermal area in the park. Because of its size and level of thermal emissions, the area also has one of the greatest geothermal radiant power outputs. The amount of geothermal power radiated by Lower Geyser Basin as determined by thermal satellite data is in the range of 200–500 megawatts. To put this into context, 1 megawatt could power several hundred homes in the U.S.
The basin is home to many well-known features, like Fountain Paint Pots, and numerous geysers, although Great Fountain Geyser is the only one that can be predicted with any confidence—it erupts about every 12 hours on average, and it has served as an analog for geysers on other planets! Also located in the basin is Mushroom Pool, where the bacteria Thermus aquaticus was discovered in 1966. That discovery eventually led to a Nobel Prize in chemistry due to the development of the Polymerase Chain Reaction (PCR) technique, which allows scientists to replicate millions of copies of a DNA sequence and is used in medical research, genome mapping projects, and even crime scene investigations.
Although the majority of the hot springs in Lower Geyser Basin are neutral to alkaline in terms of their chemical compositions, there are also some acidic hot springs. Sometimes these differences in water chemistry are in very close proximity to one another. For example, Fountain Paint Pots, which is acidic in nature, is adjacent to many neutral-alkaline geysers and hot springs. This diversity in the chemical compositions of water is in contrast to nearby Midway Geyser Basin and Upper Geyser Basin, which are both dominated by neutral-alkaline water chemistry.
Lower Geyser Basin is home to several small lakes. Sediment on the bottom of these lakes, which can be sampled via coring, records changes in climate and hydrothermal activity over time. Climate differences are also indicated by the presence of travertine near Firehole Lake. That mineral is only deposited in the caldera during cooler and wetter conditions, which apparently dominated the area a few thousand years ago.
In addition, there are multiple thermal kames—piles of glacial debris that have been cemented together by hydrothermal fluids and that suggest the region was very active in terms of hydrothermal activity even when Yellowstone was covered by a thick cap of glacial ice. The most prominent thermal kames in Lower Geyser Basin include Twin Buttes, in the southwest part of the basin, and Porcupine Hills, to the northeast.
Large hydrothermal explosion craters can also be found in Lower Geyser Basin. Pocket Basin, for example, is a hydrothermal explosion crater in the north part of Lower Geyser Basin that measures a whopping 1,200 × 2,600 feet (365 × 790 meters). Geological evidence suggests that Pocket Basin formed during the final stages of glaciation, perhaps around 13,000–14,000 years ago. Rapid draining of a glacially dammed lake may have caused decompression in the hydrothermal system present in the area, leading to the explosion.
Bubbling mudpots, colorful hot springs, spectacular geysers, massive explosion craters, important scientific discoveries, incredible geological stories, and even the oldest historic building in Yellowstone National Park…Lower Geyser Basin has it all!