Geological characteristics form the foundation of an ecosystem. In Yellowstone, the interplay between volcanic, hydrothermal, and glacial processes and the distribution of flora and fauna are intricate and unique.
The topography of the land from southern Idaho northeast to Yellowstone results from millions of years of hotspot influence. Some scientists believe the Yellowstone Plateau itself is a result of uplift due to hotspot volcanism. Today's landforms channel westerly storm systems eastward onto the plateau where they drop large amounts of snow.
The distribution of rocks and sediments in the park also influences the distributions of flora and fauna. The volcanic rhyolites and tuffs of the Yellowstone Caldera are rich in quartz and potassium feldspar, which form nutrient-poor soils. Thus, areas of the park underlain by rhyolites and tuffs generally are characterized by extensive, monotypic stands of lodgepole pine, which are drought tolerant and have shallow roots that take advantage of the nutrients in the soil. In contrast, andesitic volcanic rocks that underlie the Absaroka Mountains are rich in calcium, magnesium, and iron. These minerals weather into soils that can store more water and provide better nutrients than rhyolitic soils. This allows for more vegetative growth, which adds organic matter to the soils and results in much more fertile soils. You can see the result when you drive over Dunraven Pass or through other areas of the park with Absaroka rocks. They have a richer flora, including mixed forests interspersed with meadows. Lake sediments such as those underlying Hayden Valley, which were deposited during glacial periods, form clay soils that allow meadow communities to out-compete trees for water. The patches of lodgepole pines in Hayden Valley grow in areas of rhyolite rock outcrops.
Because of the influence rock types have on plant distribution, some scientists theorize that geology also influences wildlife distributions and movement. Whitebark pine is an important food source for grizzly bears during the autumn. The bears migrate to the whitebark pine areas such as the andesitic volcanic terrain of Mt. Washburn. Grazing animals such as elk and bison are found in the park's grasslands, which grow best in sedimentary soil of valleys such as Hayden and Lamar. And the many hydrothermal areas of the park, where grasses and other food remain uncovered, provide a haven for animals during the winter.
The park's geologic chronology spans much of the earth's history. Surrounding the Yellowstone caldera are stories of more ancient times that yield remarkable geologic treasures. The oldest rocks revealed in Yellowstone date back 2.7 billion years. These rocks are found in the northern mountains of the park and represent the very foundation of North America. Later, 500 million years ago, Yellowstone was a far different place than it is today. Covered by shallow inland seas, ocean sediments built up layer upon layer to form the common sedimentary rocks found in the park lime-stone, sandstone, and shale. And the story continues with the latest deposits of travertine on the terraces of Mammoth Hot Springs. Standing in one place in Mammoth, a visitor can see some of the oldest and newest rocks on earth at the same time. Between the time of ancient seas and the caldera-forming volcanoes of the recent past, a great period of mountain building began as the North American Plate collided with the Pacific Plate 100 to 50 million years ago. A time of tremendous upheaval, this powerful tectonic activity folded, faulted, and compressed the earth, leading to the uplift and creation of the Rocky Mountain chain.
In this unstable landscape, even more ancient volcanoes arose about 50 million years ago to form the Absaroka and Washburn mountains. Lying across Yellowstone Lake and bounding the park's east side, the Absarokas are an imposing mountain range that formed from erupting volcanoes during a 15-million-year period. To d a y, they provide a wonderful backdrop to the waters of Yellowstone Lake. At the time of their creation, they ejected silica-rich lava and ash, which mixed with water to form mudflows. These mudflows surrounded redwoods, sycamores, magnolias, dogwoods, and other trees, preserving the world's largest petrified forest as a record of an earlier climatic period. To d a y, these forests of stone can best be seen on Specimen Ridge near Lamar Valley.
Yellowstone is a land of contrasts and extremes. Just as the internal fires of the earth bring boiling water to the surface as geysers and hot springs, the park's high elevation and northern latitude also make it a land of deep snows and long winters. When more snow falls in winter than can melt in summer, ice begins to form under the weight of the snow and eventually begins to flow as a glacier. Though there are no active glaciers in Yellowstone today, such conditions have occurred here intermittently during the last two million years.
Like any good sculptor working in stone, these giant glaciers left their imprint on Yellowstone in many ways, both subtle and harsh. The region's most recent period of glaciation began about 50,000 years ago in the high mountains of the Absaroka Beartooth Wilderness, northeast of Yellowstone. With time, vast sheets of ice, thousands of feet thick, flowed from the mountains to converge over Yellowstone Lake, covering the Yellowstone Plateau and virtually all of the park and surrounding area. While thermal basins continued to seethe beneath the ice, this land of fire and brimstone was in a deep freeze for thousands of years. At the peak of this glacial era, roughly 25,000 years ago, prominent peaks like Mount Sheridan lay hidden underneath this icy blanket, while the tip of Mount Washburn and the thin ridge line of the Absaroka Mountains barely peeked above this unrelenting sea of ice. For thousands of years, ice flowed in all directions from this immense ice field, carving, scouring, and sculpting the land.
As this ice age slowly ended nearly 15,000 years ago, it left behind ample evidence of the trans-forming power of ice. Among the broad hills and benches of Hayden Va l l e y, lake sediments of silt, sand, and gravel, covered in glacial till, remain from a time when the valley was covered by an ancient lake formed by an early ice dam. Large river valleys like the Firehole, Madison, and Lamar were broadened and scoured by accompanying rivers of ice. Retreating glaciers and their meltwa-ters gradually dropped their load of rock debris. Having carried massive stones from high, far off mountains like the Beartooths, the ice melted and left behind fields dotted with large granite boulders, called glacial erratics, at places where granite is not found, like Canyon's Inspiration Point and near Lamar Va l l e y. Glacial ponds, striated hillsides, chiseled peaks, and polished mountain faces, all fashioned by the hand of ice, create some of the finishing touches on the spectacular landscape we see today.
Nowhere else in the world can we find the array or number of geysers, hot springs, mud pots, and fumaroles found in Yellowstone. More than 75% of the world's geysers, including the world's largest are here in 7 major basins. Steamboat, the world's tallest active geyser, is in the Norris Geyser Basin. Old Faithful, Grand, Castle, Giantess, Beehive, and Lion geysers may be frequently observed in the Upper Geyser Basin. Old Faithful Geyser has never been either the largest or most regular of geysers-yet, it has been the most regular and frequent geyser that erupts to a height of more than 100 feet; the average time between eruptions ranges between about 66 and 80 minutes, although occasionally visitors must wait two hours between eruptions of Old Faithful. For other major geysers in the Old Faithful and Norris geyser basins, eruption frequencies, durations, and heights change fairly often, especially in response to seismic activity; park visitors will find the most current information about specific geyser behavior patterns available at the Old Faithful Visitor Center or the Norris Museum. The park's thermal features lie in the only essentially undisturbed geyser basins left worldwide. In Iceland and New Zealand, geothermal drill holes and wells 2.5 - 6.2 miles distant have reduced geyser activity and hot spring discharge. Despite the proximity of roads and trails in the largest basins, few park features have ever been diverted for human use (such as bathing pools or energy).
Yellowstone National Park offers visitors and scientists an opportunity to appreciate thermal features in their natural, changing state. For example, research on thermophilic bacteria, algae mats, predators, and their environments is applied elsewhere to energy fuel production and extraction, bio-mining, control and removal of toxic wastes, development of new surfactants and fermentation processes, and other fields. Park features have always been subject to some influence from human vandalism. In the park's early years it was common for visitors to use thermal features as wishing wells, and this practice continues to some degree today. Coins, rocks, trash, logs or stumps, and other paraphernalia are found in the narrow vents of geysers and hot springs. Features have been plugged up, and little can be done to repair the damage. Radical attempts to siphon surface water and induce eruptions have occasionally been tried on famous features such as Morning Glory Pool, with varying degrees of success. Damage also occurs when people leave walkways and climb on features, or occasionally break pieces of sinter or travertine off for souvenirs (Marler 1973). Features can also be affected by nearby ground-disturbing activities. The presence of water, sewer, and other utility systems adjacent to thermal areas has likely affected features in the past. Since many major features are located near roads and developed areas, major maintenance and construction activities must be carefully designed and monitored so as not to alter thermal features. Periodically, applications are made for geothermal leases in Known Geothermal Resource Areas (KGRAs) outside the park, such as in the Island Park KGRA west of the park, and the Corwin Springs KGRA north of Yellowstone National Park near LaDuke Hot Springs.
A rapid change in energy economics could increase pressure to open non-federal lands to leasing and drilling activity. Thus, research is needed to determine the extent to which Yellowstone National Park's geothermal systems connect with areas of lease application west and north of the boundary. Volcanic and seismic processes are very active in the park. A network of seismic monitoring stations in the park provides data to help understand overall seismicity in the region and gauge the magnitude of earth tremors. Thermal features and basins respond violently to volcanic/seismic activity, which creates both a serious hazard to humans and an opportunity to study and possibly predict major geologic hazards. Thus, maintenance of a long-term geothermal data base also helps us manage visitor use to increase public safety in a naturally hazardous environment. Legislative restrictions on geothermal development around Yellowstone, such as the Old Faithful Protection Act introduced in 1992, have failed to pass Congressional approval. In 1994, the NPS and the state of Montana agreed to monitor and control the use of hot, warm, and cold groundwater in areas just north of the park. Proponents of water use must show that proposed geothermal development will not adversely affect park features. This Water Rights Compact could serve as a model for agreements between the park and other states to ensure the continued flow of heat and water to Yellowstone's famous geysers and hot springs. References Marler, George. 1973. Inventory of Thermal Features of the Firehole River Geyser Basins and Other Selected Areas of Yellowstone National Park. Natl. Tech. Info. Serv., U.S. Dept. Commerce. Pub. PB221 289. 652p.
Additional Geothermal Resources Information
A great deal of data is being collected and interpreted by our friends at the Yellowstone Volcano Observatory.