The Hawthornes had only two days to explore Yellowstone Park. The first day, we went down the east side. The second day, we went down the west side. I could have spent a month just traveling by vehicle to see the different sites, not to mention the hiking trails which we were unable to experience due to time constraints, arthritis, improper walking shoes, lack of bear mace, general laziness, and a multitude of other "excuses." In our two days in Yellowstone, we tried to hit the highlights, but it's impossible to see everything. As Mr. Hawthorne says, "We gotta leave something for next time." What immediately struck me were the obvious geological differences between East and West Yellowstone. East Yellowstone is more mountainous. West Yellowstone is blatantly precarious and fragile. It's thin-crusted. It's under pressure. It's ready to blow. And it does frequently. It vents. Constantly. It's geologically and physically one scary Mo-Fo. Please click to enlarge and check out the map of Yellowstone. The red line shaped like a figure eight is the road in Yellowstone. If you notice, it is situated atop a giant caldera - the dotted black line. As I've said before, the past, present, and future of Yellowstone is shaped by volcanism. Did you think you were getting away without a history/geology lesson? 2,000,000 years ago, 1,300,000 years ago, and 640,000 years ago, catastrophic volcanic eruptions occurred here. These three caldera-forming eruptions were about 2500, 280, and 1000 times larger respectively than the May 18, 1980 eruption of Mt. St. Helens in Washington State. The initial eruption 2 million years ago is thought to be the largest, most violent eruption in the earth's history. Enough ash and volcanic debris exploded from the eruption to cover the entire western half of the United States with about a four-foot deep layer of ash. Roughly 600 cubic miles of material were thrown into the atmosphere. The last eruption spewed out over 240 cubic miles of debris and the park's present central portion collapsed, creating a giant 30 by 45 mile caldera or basin. Most of the world's caldera-forming volcanoes are found over subducting tectonic plates, meaning one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle as the plates converge. Subduction zones are noted for their high rates of volcanism, earthquakes, oceanic trench formation, and mountain building. In the Earth, there are currently 7-8 major tectonic plates. These plates make up the lithosphere of the Earth. Plate tectonics is a scientific theory which describes the large scale motions of the Earth's lithosphere. The lithosphere is the hard and rigid outer layer of Earth and is broken up into what are called tectonic plates. The lithosphere rides atop the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. These plates move in relation to one another at one of three types of plate boundaries: convergent, or collisional, boundaries; divergent, or spreading, boundaries; and conservative transform boundaries. Convergent boundaries occur where two plates slide towards each other, forming a subduction zone if one plate moves underneath the other, or a continental collision if the two plates contain continental crust. Examples are the Andes mountain range and the Japanese island arc. Divergent boundaries occur where two plates slide apart from each other. Examples include the Mid-Atlantic Ocean Ridge and Africa's Great Rift Valley. Transform boundaries occur where plates slide, or perhaps more accurately, grind past each other along transform faults. An example is the San Andreas Fault in California. Unlike most of the caldera-forming volcanoes that are found over subducting plates, the Yellowstone Caldera is fed by what geologists call a hotspot beneath the crust. This theory explains how volcanic activity can occur in the middle of tectonic plates, away from geologically active plate margins. A hotspot, or enormous magma chamber, lies in wait beneath the enormous Yellowstone Caldera. Scientists have surveyed the ground in the caldera and have found that it seems to be bulging upward, an indication of a magma chamber on the move. Since there are no historical/geological precedents for this type of eruption, scientists do not know how to predict if a giant caldera-forming eruption will occur again. This violent volcanic activity has most prevalently shaped Yellowstone's topography. Biodiversity - from microorganisms to moose - has been shaped and formed by Yellowstone's underlying geology. Processes of glaciation, physical weathering, and mountain uplift have shaped the landscape, and have influenced both mountain and forest geography. Because of the tremendous biodiversity protected within Yellowstone, the Park was declared an International Biosphere Reserve in 1976 and a World Heritage Site in 1978. The Greater Yellowstone Ecosystem, with Yellowstone National Park as its core, is a 20 million acre expanse of mountainous wildlands spread over three states - Idaho, Montana, and Wyoming. Yellowstone is on a high plateau averaging 8000 feet in elevation. The mountain ranges surrounding Yellowstone vary from 10,000 feet to nearly 14,000 feet. A unique cradle of life, the Greater Yellowstone Ecosystem is the last intact contiguous temperate ecosystem in the world. River systems, elevation, mountain topography, wildlife ranges, characteristic flora and fauna, and human-use patterns are unparalleled inside the Greater Yellowstone Ecosystem when compared to the surrounding lands. The GYE still contains nearly all of the living organisms found in pre-Columbian times, though not in the same numbers. The unique ecosystem, biodiversity, and geologic features are intimately related to the geologic history of Yellowstone. Glaciation, tectonic activity, and most importantly, volcanic eruptions, have shaped and influenced the landscape and life within the park. Yellowstone contains over 10,000 thermal features. Between 300 and 500 are active geysers. Conservatively, over 55% of the world's geysers reside in Yellowstone. Within these thermal features can be seen the product of millions of years of geology at work. For hundreds of thousands of years following the last volcanic eruption, subsequent lava flows slowly filled in most of the giant caldera. Even now, in some places, molten rock resides as little as 2-3 miles below the surface. Intense heat from the volcanic activity makes its presence known by heating ground water and creating the thermal features we now see in Yellowstone. There are four basic types of thermal features present in the Park.
- Geysers. Geysers are hot springs that erupt periodically. The eruptions are the result of super-heated water below ground becoming trapped in channels leading to the surface. The hottest temperatures are at the bottom of these channels, nearer the hot rock, but the deeper water cannot vaporize because of the weight of the water above. Instead, steam is sent upwards in bubbles, collecting in the channel's tight spots until they essentially become clogged. This leads to a point where the clogged bubbles actually lift the water above, causing the geyser to overflow. As the pressure decreases from the overflow, violent, sudden boiling occurs throughout much of the length of the column, producing a tremendous volume of steam which forces the water out of the vent in a superheated mass. This is an eruption and as the eruption continues, the heat and pressure gradually decrease. The eruption ceases when the water reservoir is depleted or the steam runs out.
- Hot springs. Hot springs are similar to geysers, but their underground channels are not large enough to allow rapid circulation of water. The plumbing system is slow so that pressure is released gradually as water reaches the surface. Rising hot water releases heat energy by evaporation or by hot water runoff. Convection currents return the cooler water to the underground system, thus maintaining an equilibrium.
- Fumeroles. Fumeroles are vents or holes from which steam rushes into the air. It's like a hot spring, but lacking liquid water. Either the underground rock is too hot and boils off all the water so a pool can't form or there isn't enough water to begin with. The small amount of water that does seep into the area is converted to steam and expelled from the steam vents, small cracks in the surface of the ground. Oftentimes this pressurized steam from below creates an audible hissing noise when it escapes to the surface.
- Mudpots. Mudpots are thermal areas where water-saturated sediment, similar to clay, is affected by super-heated steam from below. Hot water is limited and the pH of the thermal waters is very acidic. The acid waters dissolve the surrounding rock into silica and clay. Not enough water is present to carry away the dissolved rock so it mixes with the water and creates this thick muddy bubbling feature. The rising steam forces its way upwards, bursting through the mud and ground water, sending showers of mud into the air, as if in a small explosion.