What States Would Be Destroyed if Yellowstone Erupts?

The Yellowstone Supervolcano, hidden beneath the surface of Yellowstone National Park, is one of the most powerful geological features on Earth. Its last major eruption occurred approximately 631,000 years ago, and scientists continue to monitor it closely due to its explosive potential. Though a supereruption is highly improbable in the foreseeable future, understanding its possible consequences is essential—not just for residents of the region but for all of North America.

So, what states would be destroyed or severely impacted if Yellowstone erupts? The answer depends on the scale and style of the eruption, but a full supereruption could spell disaster for large portions of the western and central United States.

The Nature of a Supereruption

Yellowstone is classified as a supervolcano, meaning it is capable of ejecting over 1,000 cubic kilometers (240 cubic miles) of material in a single eruption. This is over 2,500 times the volume of the 1980 Mount St. Helens eruption.

Rather than forming a towering cone like Mount Rainier or Mount Fuji, Yellowstone’s eruptions collapse the ground, forming a caldera—a massive craterlike depression. The current Yellowstone Caldera spans roughly 30 by 45 miles and sits atop a vast reservoir of partially molten rock.

If Yellowstone erupted on the scale of its past three supereruptions—Huckleberry Ridge (2.08 mya), Mesa Falls (1.3 mya), and Lava Creek (631,000 years ago)—the impact would be catastrophic. The destruction would not be limited to Wyoming; it would extend far beyond state borders.

States That Would Be Completely Devastated

1. Wyoming

Ground zero. Yellowstone National Park is located in the northwest corner of Wyoming, and the state would absorb the brunt of the eruption’s violence. Pyroclastic flows—fast-moving clouds of superheated gas and volcanic debris—would obliterate everything within a 30- to 60-mile radius of the caldera. Entire ecosystems would be incinerated. Cities such as Jackson, Cody, and possibly even Casper could be completely destroyed.

2. Montana

Southwestern Montana, especially areas like Bozeman, Big Sky, and Billings, lies just north of the caldera. Ashfall here could reach several feet in thickness, collapsing roofs, contaminating water supplies, and rendering agriculture impossible. Infrastructure would fail, and long-term evacuation might become necessary.

3. Idaho

Eastern Idaho, including cities like Idaho Falls and Rexburg, lies just west of Yellowstone and would likely suffer severe pyroclastic flows or extremely heavy ashfall. These regions could be rendered uninhabitable for decades, if not centuries.

States Facing Extreme Ashfall and Societal Collapse

4. Utah

Though not in the blast zone, northern Utah—including Salt Lake City—could be blanketed with several inches of ash. Volcanic ash is not like soft campfire ash; it’s fine, glassy, and abrasive. Even 1–2 inches can disable vehicles, short out electronics, contaminate air and water, and collapse roofs.

5. Colorado

Central and eastern Colorado could receive ash depths of 1–5 inches depending on wind patterns. Denver, Fort Collins, and Colorado Springs would face severe air quality hazards, disruption to transportation, and a possible breakdown of municipal systems.

6. Nebraska and the Dakotas

Prevailing winds (generally west-to-east in the U.S.) would carry massive ash plumes across the Great Plains. Nebraska, South Dakota, and North Dakota could be buried in inches of ash. This would devastate farmland, pollute water, and destroy machinery. Electricity and water purification systems would likely fail.

States Affected by Moderate to Light Ashfall

7. Kansas, Iowa, and Missouri

States like Kansas City, Des Moines, and St. Louis would see light to moderate ashfall, depending on atmospheric conditions. A few inches of ash may not seem life-threatening, but even this level can grind transportation, communication, and trade to a halt.

8. Illinois, Indiana, and Ohio

By this stage, ash layers might only be a fraction of an inch thick—but enough to infiltrate HVAC systems, disrupt aviation, and create significant public health concerns. These areas could face food shortages and supply chain disruptions due to problems farther west.

The Rest of the United States: Indirect but Widespread Consequences

While the Pacific Northwest, Southeast, and Northeast might escape the worst ashfall, they would not be immune to disaster:

• Air travel across North America and the North Atlantic would likely be grounded for weeks or months.

• Volcanic winter could lower global temperatures by 3–5°C (5–9°F) for years, causing massive crop failures across the Midwest and worldwide.

• Water contamination and shortages could affect even distant states as ash chokes river systems and reservoirs.

• Mass migration from the central and western U.S. could create political and humanitarian crises.

Would the Entire U.S. Be “Destroyed”?

The word “destroyed” can mean different things in this context. If we define it as total physical obliteration, then the destruction would be largely confined to:

• Northwestern Wyoming
• Southwestern Montana
• Eastern Idaho

However, if we define “destruction” as collapse of infrastructure, economy, agriculture, or livability, then nearly all of the continental United States would suffer to some degree.

Could People Survive a Yellowstone Eruption?

Yes—but survival depends on location, preparedness, and resilience. Those within a few hundred miles of the eruption would need immediate evacuation, gas masks, and access to clean water. In the long term, surviving the aftermath would require:

• Stable food and energy sources
• Functioning government and emergency management systems
• Global aid and cooperation

How Likely Is a Yellowstone Supereruption?

According to the U.S. Geological Survey (USGS), the chance of a Yellowstone supereruption in any given year is approximately 1 in 730,000. Smaller hydrothermal explosions or lava flows are more likely but far less destructive.

Still, Yellowstone is monitored constantly by scientists using GPS, satellite imagery, and seismic sensors. At present, there are no signs of imminent eruption.

Final Thoughts

A Yellowstone supereruption would be a continent-altering event. While Wyoming, Montana, and Idaho would face the greatest physical destruction, dozens of states across the country could face life-altering consequences. Ashfall, climate effects, infrastructure collapse, and mass displacement would fundamentally alter life in the United States—and reverberate globally.

Though such an eruption is extremely rare, it's a sobering reminder of nature’s power and our need for scientific vigilance and disaster preparedness.