A sleeping giant is nestled in the western part of the United States. Though it stirs occasionally, it has not risen from slumber in nearly 70,000 years. But when it finally awakes it may roar and heave with unprecedented force.

This giant is the “supervolcano” that lies beneath Yellowstone National Park, the wildlife and forest preserve positioned on a sprawling expanse that extends through the states of Wyoming, Idaho, and Montana. The volcano itself is actually located in northwestern Wyoming, which is where the bulk of Yellowstone is contained.

The ground above the Yellowstone supervolcano sits on a hot spot made of molten and semi-molten rock called magma. As magma feeds into a magma chamber, or reservoir situated about 6-10 kilometers (4-6 miles) beneath the park, the ground swells. When the magma begins to solidify and cool, the ground falls. 

Volcanologists, who have been measuring this activity since 1923, say the ground rose about 25 centimeters (9.8 inches) between 2004 and 2009. However, in 2010 the land began to subside. 

The period of slow, steady rise has many scientists wondering whether Yellowstone might erupt in the near future. And if it does, there is concern about how intense that eruption may be. 

“The big question is if Yellowstone started shaking tomorrow, what is there to expect?” says Dr. Steve Anderson, a volcanologist and earth sciences professor at the University of Northern Colorado. “I don’t think we know exactly what to expect.”

While scientists may not know exactly what to expect, they have an idea—and most say it’s unlikely to be doomsday. 

In fact, Dr. Jacob Lowenstern, research geologist and Scientist-in-Charge at the Yellowstone Volcano Observatory, says that Yellowstone is currently a dormant volcano, with low levels of unrest. 

“There is no current activity that is going on that would indicate anything is happening. If there was something coming, there is nothing to show at this point in time,” he says. 

Learning from the Past

Still, the level of recent underground activity fuels speculation about the intensity of an eruption. Within the past decade, the volcano has continued to rise at the fastest rate ever recorded.

 

Yellowstone also averages between 1,000 and 3,000 earthquakes a year. Most are virtually unnoticeable, with a magnitude of three or less. Still, these quakes give scientists insight into just how fast the magma chamber beneath the park is filling up. An increase in the shaking and rattling throughout the park might indicate a fresh batch of magma was recently fed into the reservoir. 


Even with the increase in temblors, scientists don’t think the rumblings in the magma chamber pose a threat anytime soon. However, since people haven’t been around to analyze absolutely everything that happens in Yellowstone, it’s hard to predict what exactly is going on, making it difficult for geologists to predict Yellowstone’s next move. 

Examinations of the volcano’s distant past do provide something of a clue. Geologic evidence suggests that Yellowstone has produced three colossal eruptions within the past 2.1 million years. Volcanologists say the eruptions occurred at gaps of about 600,000 to 800,000 years. Evidence from the last big event, estimated to have to been about 640,000 years ago, is sprawled throughout the park and across thousands of kilometers of the surrounding landscape

Each of the previous eruptions spewed enormous amounts of volcanic ash, gas, magma, and other volcanic debris that covered most of the continental U.S. Some material has been found as far away as Louisiana.

After each of these eruptions, the Yellowstone supervolcano collapsed on itself, sucking in trees, mountains and everything else in the landscape. The depression formed by this phenomenon is called a caldera. (In fact, the Yellowstone supervolcano is also called the Yellowstone caldera.) A caldera-forming eruption would create a massive natural hazard in Yellowstone. 

Scientists say the last Yellowstone eruption was 1,000 times greater than the notorious 1980 Mt. Saint Helens eruption that killed 56 people and thousands of animals, and scorched hundreds of square kilometers of land in Washington and Oregon. 

Thousands of years ago, the last blast from the Yellowstone supervolcano shot a fatal plume of hot ash, molten rock, and lethal gases thousands of meters into the air. A third of the continent was likely plunged into complete darkness. Pyroclastic flows (fast-moving currents of hot, dry rock fragments and gases) raced along the region at alarming speeds, burying or shattering anything in their path. Magma spewing out of the ground charred the once-charming landscape for kilometers.  

Some evidence of the last eruption can be found in the Yellowstone caldera itself, 50 kilometers (30 miles) wide and 70 kilometers (45 miles) long. The thick volcanic debris that remained after the eruption can still be seen in an area referred to as the Lava Creek Tuff.  


Unlikely to Erupt

Officials of the United States Geological Survey (USGS) say a massive eruption like the last one is an unlikely scenario. In fact, officials at the Yellowstone Volcano Observatory say the most likely activities that might take place in the future are hydrothermal explosions (eruptions of steam and hot water, rather than molten rock) or lava flows.

Although lava flows are a type of magmatic eruption, they are not as devastating as the caldera-forming explosions. Instead of instant destruction, lava flows slowly ooze out of the ground over a period of days, months, or even years. 

They are also relatively rare. The last Yellowstone lava flows took place about 70,000 years ago. Yet even today, hikers can see evidence of those eruptions in the form of distinct rock layers along the park’s trails. Some evidence of younger lava flows can be found near the cliffs surrounding the Upper Geyser Basin, near Old Faithful. (Old Faithful is a geyser and one of the park’s most popular tourist attractions.)

Today, Yellowstone sleeps, with scientists checking its every hiccup or cough in an effort to predict its next move. While the brewing force beneath the park has been restrained for thousands of years, Yellowstone’s dormancy does not mean it will not one day awaken. The question remains: When and with what force?

“We are getting into the time period where it is supposed to become more unstable,” says Anderson, “but I am not holding my breath.”

 

When a Sleeping Giant Awakes
Like many calderas, the Yellowstone caldera includes a lake (Yellowstone Lake).

Hot Water
Yellowstone's current geologic activity is limited to hot springs and geysers. Old Faithful, the park's most famous geyser, spews more than 14,000 liters (3,700 gallons) of boiling water more than 30 meters (100 feet) in the air every 91 minutes.

Migrating Eruptions
Like all volcanic hot spots, the Yellowstone hot spot has remained stable for millions of years, while the North American continent has drifted southwest. The oldest eruptions associated with the Yellowstone hot spot occurred in what is today the southeastern part of Oregon. The most recent eruptions have been in the northeast corner of Wyoming.

Supervolcanoes
Supervolcanoes are loosely described as volcanoes that produce more than 1,000 cubic kilometers (240 cubic miles) of gas, ash, magma, and rock. Those that erupted less than 100,000 years ago include:

  • Lake Toba, Indonesia
  • Yellowstone, United States (Idaho and Wyoming)
  • Lake Taupo, New Zealand
Noun

large depression resulting from the collapse of the center of a volcano.

char
Verb

to burn.

Noun

steep wall of rock, earth, or ice.

debris
Noun

remains of something broken or destroyed; waste, or garbage.

dormant volcano
Noun

volcano that has erupted in the past but is unlikely to erupt soon.

earthquake
Noun

the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

erupt
Verb

to explode or suddenly eject material.

geologist
Noun

person who studies the physical formations of the Earth.

Noun

natural hot spring that sometimes erupts with water or steam.

Noun

intensely hot region deep within the Earth that rises to just underneath the surface. Some hot spots produce volcanoes.

hydrothermal
Adjective

related to hot water, especially water heated by the Earth's internal temperature.

Noun

the geographic features of a region.

lava
Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

lethal
Adjective

deadly.

Noun

molten, or partially melted, rock beneath the Earth's surface.

magma chamber
Noun

underground reservoir that holds molten rock.

molten
Adjective

solid material turned to liquid by heat.

natural hazard
Noun

event in the physical environment that is destructive to human activity.

Noun

current of volcanic ash, lava, and gas that flows from a volcano.

steam
Noun

water vapor.

supervolcano
Noun

volcano capable of ejecting more than 1,000 cubic kilometers (240 cubic miles) of material.

temblor
Noun

earthquake.

tuff
Noun

type of rock formed from hardened volcanic ash.

unprecedented
Adjective

never before known or experienced.

Noun

(United States Geological Survey) primary source for science about the Earth, its natural and living resources, natural hazards, and the environment.

Noun

fragments of lava less than 2 millimeters across.

volcanologist
Noun

scientist who studies volcanoes.