Landscape & Geology

The Yellowstone and Grand Teton region is one of the most dynamic seismic areas in the world -- wracked by earthquakes, cracked by water boiling to the surface, and littered with the detritus of previous volcanic eruptions. Today, the bowels of the Yellowstone caldera are again filling with magma. Geologic studies show that, for the last 2 million years, the plateau has blown its top every 600,000 years or so -- and the last explosion was about 600,000 years ago. That means that a titanic blow -- bigger than anything seen in recorded history -- could happen, well, any century now, give or take 10,000 years. The geological time frame is a long one, by human standards.

As you'll learn when you visit the exhibits on the park's geology at Moose, Mammoth, and the various geothermal areas, what you see on the surface -- great layers of ash and the core of volcanic vents, such as Mount Washburn and Bunsen Peak -- is only a fraction of the story of Yellowstone and Grand Teton.

Situated on 2.2 million acres, Yellowstone is significantly larger than its sister to the south. Encompassing 3,472 square miles, Yellowstone boasts 370 miles of paved roads and 1,200 miles of trails, and it is home to more geysers and hot springs than the combined total in the rest of the world.

Although it can't match Yellowstone's size, Grand Teton National Park is nothing to sneeze at. It has towering mountain spires, that have been compared to cathedral towers, reaching almost 14,000 feet skyward, picturesque glacial lakes, and a great deal of interesting topography. The 485 square miles of Grand Teton contain about 160 miles of paved roads and over 250 miles of hiking trails.

Geysers, Hot Springs, Mud Pots & Fumaroles: What's the Difference?

Here's a way to identify the four most common types of thermal attractions in Yellowstone:

Geysers, the most prominent and spectacular of the thermal features in the park, are formed by the marriage of three elements: heat in the center (mantle) of the earth, water, and pressure-resistant rock. Here's how they work together: The water source comes in the form of snowmelt that sinks into the Earth, reaching depths of 10,000 feet -- that's 2 miles, but, remember, thermal areas in Yellowstone are that close to the surface. The second element is heat, which is provided by the cauldrons of magma. When water moves toward the center of the Earth, the heat brings it to a boil and sends it back toward the surface, often with traces of numerous minerals. The third element, pressure-resistant rock, acts like a geologic traffic cop by guiding the water toward the surface. Because the geyser's plumbing system does not have a way to diffuse energy, pressure builds, the boiling water is converted to steam, and boom! Plumes of steam are spewed forth from vents in the Earth's surface. Following the eruptions, silica that once was a component of the magma returns down the pathway to form a lining through which more snowmelt will travel, and the process repeats itself.

Hot springs are closely related to geysers but don't display the same eruptions because they don't develop the same subsurface pressures. Their colorful appearance is a result of different minerals, algae, the absorption of light by colloidal particles -- tiny, suspended particles -- and reflections.

Mud pots are hot springs on the Earth's surface that are formed as heated water mixes with clay and congealed minerals. Some mud pots are very colorful; others are unsightly and smelly.

Fumaroles are steam vents known as "dry geysers," from which gases rush into the air; they are considered hot springs that lack a liquid component.

The Faces of Yellowstone Park

By the completion of the 1872 Hayden expedition, explorers had identified several distinct areas in the park, each with its own physical characteristics. Less spectacular than the craggy mountain scenery of Grand Teton, and less imposing than the vast expanses of the Grand Canyon of Arizona, Yellowstone's beauty is subtle, reflecting the changes it has undergone during its explosive past.

Although Yellowstone has its share of mountains, much of the park is a high mountain plateau. The environment changes dramatically as you ascend the mountain slopes from the foothill zones in the valleys -- the elevation at the entrance at West Yellowstone is 6,644 feet, for example, compared to 5,314 at the Gardiner entrance. Because the park lies about halfway between the equator and the North Pole, its summers consist of long, warm days that stimulate plant growth at the lower elevations.

As you walk the park trails, you'll find that plant distribution changes with the elevation. At the lowest elevations, down around 5,000 feet above sea level, you'll find grassy flats and sagebrush growing on dry, porous soils, with creeks and rivers cutting through to form wildlife-rich riparian zones. Next up: the foothills, sloping upward toward peaks, sometimes dotted by deposits of glacial moraine. Douglas fir, pine, and other conifers, as well as stands of aspen, clad these slopes, and there are marshes and ponds fed by the spring snowmelt. Shrubs and flowers, such as huckleberry and columbine, favor these wet, shady spots.

Then comes the mountain zone (6,000-7,600 ft.), thickening forests dominated by lodgepole pine, broken by meadows where deer, elk, and moose often graze. The transition area between the highest forest and the bare surface above timberline is known as the subalpine zone (7,600-11,300 ft. of elevation). Finally, we come to the bare rock at the very top of the continental shelf, where small, hardy plants, such as glacier lilies and sky pilot, bloom briefly after the annual thaw.

Although the park is most famous for its geysers, visitors can choose among very different environments, reflections of the long-term effects of geologic activity and weather.

The limestone terraces at Mammoth Hot Springs give testimony to the region's subsurface volcanic activity. The park sits atop a rare geologic hot spot where molten rock still rises to within 2 miles of the Earth's surface, heating the water in a plumbing system that still mystifies scientists.

The northern section of the park, between Mammoth Hot Springs and the Tower-Roosevelt region, is a high-plains area that is primarily defined by mountains, forests, and broad expanses of river valleys that were created by ice movements.

The road between the Tower-Roosevelt junction and the northeast entrance winds through the Lamar Valley, an area that has been covered by glaciers three times, most recently during an ice age that began 25,000 years ago and continued for 10,000 years. In geologic terms, that was yesterday. Because this area was a favorite spot of Theodore Roosevelt, it is often referred to as "Roosevelt Country." The beautiful valley where elk, bison, and wolves interact is still dotted with glacial ponds and strewn with boulders deposited by moving ice.

Farther south are Pelican and Hayden valleys, the two largest ancient lakebeds in the park. They feature large, open meadows with abundant plant life that provides food for a population of bison and elk.

In the warm months, you'll enjoy the contrast between the lush green valleys and Canyon Country, in the center of the park. Canyon Country is defined by the Grand Canyon of the Yellowstone, a colorful, 1,000-foot-deep, 24-mile-long gorge -- in many opinions, just as dramatic as its cousin in Arizona. The Yellowstone River cuts through the valley, in some places moving 64,000 cubic feet of water per second, creating two waterfalls in the process, one of which is more than twice the height of Niagara Falls.

When you arrive at the southern geyser basins, you might feel that you've been transported through a geologic time warp. The cratered landscapes here are unlike any other in the park. Here you will find the largest collections of thermal areas in the world -- there are perhaps 600 geysers and 10,000 geothermal features in the park -- and the largest geysers in Yellowstone. The result: boiling water that is catapulted skyward and barren patches of sterile dirt; hot, bubbling pools that are unimaginably colorful; and, of course, the star of this show, Old Faithful geyser. Plan on spending at least 80 minutes here because that's the typical period between eruptions that send thousands of gallons of boiling water through the sky at a speed exceeding 100 mph.

You'll see the park's volcanic activity on a 17-mile journey east to the lake area, the scene of three volcanic eruptions that took place more than 600,000 years ago. When the final eruption blasted more than 1,000 square miles of the Rocky Mountains into the stratosphere, it created the Yellowstone caldera, a massive depression measuring 28x47 miles, and Yellowstone Lake basin, some 20 miles long and 14 miles wide, reaching depths of 390 feet. You'll notice, as you travel the roads here, that the landscape consists of flat plateaus of lava that are hundreds of feet thick.