Geology and Ecology of National Parks

Yellowstone National Park

Overview

Yellowstone National Park is a UNESCO World Heritage Site in northwest Wyoming, southern Montana, and eastern Idaho. The park was created March 1, 1872 as the first national park in the world and encompasses over 2,000,000 acres (3472 square miles) of wilderness. Yellowstone is home to a wide range of unique plants and animals seen in few other places in the country. Herds of bison and newly reintroduced packs of gray wolf roam the Yellowstone Plateau in close proximity to visitors. In addition to the diverse ecology of the park, Yellowstone’s geologic features attract over four million tourists each year. Much of the park rests on top of a shallow body of magma which drives the nearly 500 geysers within the park, including Old Faithful. This body of magma has erupted multiple times in the last several million years, creating three different calderas and producing some of the largest volcanic eruptions the world has ever seen.

 

Geologic History

Like the rest of the Rocky Mountains, this area was once a flat basin covered by the Western Interior Seaway until roughly 66 million years ago. Shortly after, the Laramide Orogeny (mountain-building event) began to uplift the Rocky Mountains. From ~50-40 million years ago, widespread volcanism, seismic activity, and mountain building also produced the Absaroka Range which borders the park’s north and eastern sides.

 

Super Volcano

Yellowstone National Park sits above three calderas (volcanic craters) which were the result of a series of supermassive volcanic eruptions starting just over two million years ago. Yellowstone is known as a super volcano because it has had at least one eruption in which 240 mi3 (1000 km3) or more of material was erupted, which is also the threshold for the highest magnitude 8 eruption on the Volcano Explosivity Index (VEI). The first and largest of these known eruptions occurred ~2.1 Ma (million years ago) and is one of the largest eruptions ever studied. The caldera produced is ~ 47 miles (75 km) wide with a surrounding ash fall, known as the Huckleberry Ridge Tuff, covering 588 mi3 (2450 km3). The second eruption occurred ~1.3 Ma, and deposited the smaller Mesa Falls Tuff, covering 67 mi3 (280 km3). The most recent eruption occurred ~640,000 years ago and marks the last super eruption. This volcanic activity released 240 mi3 (>1000 km3) of ash, creating the Lava Creek Tuff, as well as the 30 by 45-mile-wide Yellowstone Caldera. Volcanic activity has occurred more recently between 180,000-70,000 years ago, but these were lava flows and not super eruptions. There is a low risk of an eruption occurring anytime soon, but scientists still use advanced satellite radar imagery, seismographs, and more to detect any vertical or horizontal changes in ground movements.

 

Magma and Hot spots

The pressure from the underlying magma body deforms the land surface throughout the caldera, but most extensively in two resurgent domes. These domes, known as Sour Creek and Mallard Lake Domes, occur as the pressure in the magma chamber increases, causing uplift in the land above it. As magma or hydrothermal fluids leave the chamber the domes drop back down and continue to shape the landscape. It is estimated that magma is as close as 3-8 miles beneath Sour Creek Dome and between 8-12 miles beneath Mallard Lake Dome. The location of the eruptions has moved eastward over the past ~16 million years as the tectonic plate has ridden over a relatively stationary heat source. This is what is known as “hot spot” volcanism and is the same process that is responsible for the formation of the Hawaiian Islands in the Pacific. To think about how a hot spot works, imagine holding a paper plate over a candle on a birthday cake (note: do not try this at home). The candle will burn a hole in the plate. If you move the plate a few inches in one direction, the candle will burn another hole. Move it again in the same direction and it will make another hole. The line of holes shows where the plate has been in the past, and the direction in which it has moved. About 16 million years ago, heat convection in the mantle caused a plume of hot magma to rise close to the surface, melting rock and heating up the crust along the way. This plume came to rest and created a reservoir of magma, the source of the heat and energy that caused the massive super volcano eruptions. When the magma plume first reached for the surface it was in Northern Nevada, but over the last ~16 million years the hot spot has moved through Southern Idaho and into its current location in northwestern Wyoming in Yellowstone National Park.

 

Seismic and Hydrothermal Activity

Earthquakes are abundant in Yellowstone National Park, averaging 1,000-3,000 per year, but most are too small to be felt.

A geyser is a hydrothermal feature, formed as A shallow magma chamber heats up the overlying rock and groundwater. When enough heat and pressure build up, the water rushes toward the surface and rises into the sky. Old Faithful, one of the most well-known geysers in the world, was named for being so predictable is one of many hydrothermal features found in the park. 

 

Map of Yellowstone National Park

Yellowstone National Park Map

(Courtesy: National Park Service)

 

To learn more about Yellowstone National Park, visit the National Park Service website.