Yellowstone Caldera Eruption: What to Expect

Mt. Vesuvius. Mt. Saint Helens. Krakatoa. Kilauea. Famous volcanoes, every one, and all have histories as great destroyers and disruptors of civilizations. Here in the U.S., the relatively recent eruption of Mt. Saint Helens is remembered for its severe local destruction and regional effects.

But there is another volcano in the continental U.S., one that is possessed of destructive might geometrically greater than Mt. Saint Helens, or those puny things that make up the Hawaiian island chain. That volcano is…

You will sometimes hear preppers discuss plans to deal with a supervolcano eruption. Well friends, this is a big one, and one that is in our own backyard. If the Yellowstone caldera were to erupt, it would have catastrophic, perhaps even worldwide consequences. In this article, we’ll be examining this giant volcano, and its potential effects in detail.

Is Yellowstone a Serious Volcano?

Wait, Yellowstone? Like, geysers, grizzlies and bison Yellowstone National Park? Yes, reader. Yellowstone, while well known for its abundant wildlife and geothermal geyser activity, is also the site of truly immense volcano, and one that is not obvious to the eye.

In fact, the spectacular geysers (which bring in loads of people every year to see them) are actually symptoms of volcanic activity. In fact, scientific and public concerns over a major eruption have been escalating steadily in recent years.

A full-scale eruption of the Yellowstone caldera would make the St. Saint Helens eruption look like a party popper.

While it does not look like a glowing, smoking mountain of doom, the Yellowstone caldera is so named because of how it is shaped; a caldera is a depressed area resembling a crater, and was formed because previous eruption events were so titanic and ejected so much material from beneath the ground the surrounding area sank.

This supervolcano’s overall size measures 34 by 45 miles, an immensity that is difficult to comprehend.

The United States Geological Survey has estimated that approximately 2/3rds of the continental U.S. was covered with ash fall after one of the Yellowstone calderas historic eruptions. There is no reason to suspect that a similar eruption in the future would occur on a smaller scale.

How Bad is a Volcano Really?

It depends on how you quantify “bad.” The good news is, most volcanoes aren’t potentially powerful enough to devastate entire regions. Most regularly active volcanoes erupt periodically with some magma ejection, choking smoke and ash and perhaps flying chunks of screaming hot rock. Sure, they can be locally destructive, even disastrously so, but you aren’t talking about anything world-ending with them.

The bad news is, Yellowstone is not one of those. It and other supervolcanoes are huge threats that can erupt with titanic explosive force, leveling a considerable area before the arrival of typical volcano threats like toxic gas, choking ash, and fast moving magma flows. Flaming hot debris can be thrown far and wide, with each mass representing a significant fire hazard.

The U.S. Geological Survey compares and quantifies volcano eruption magnitude on a scale called the Volcano Explosivity Index, or VEI. The scale goes from zero, the volcano equivalent of a pop-gun, to eight, which is cataclysmic and the point at which point a volcano earns the “supervolcano” classification.

Contrast with the 1980 Mt. Saint Helens eruption; as bad as that was, that was only a six on the VEI index. Yellowstone is a strong eight on the scale, and has already erupted 3 times on a colossal scale in the past, each of them several thousand times more destructive than Mt. Saint Helens.

A supervolcano can eject over 250 cubic miles of volcanic material over an extremely wide area and high, high into the atmosphere. Previous Yellowstone eruptions have been analyzed by scientists and ash from them has been calculated to have covered an area totaling more than half of the continental United States. The effects on agriculture, people, animals and machines will be terrible and likely on a worldwide scale.

The most spectacular lethal element from a volcano is the pyroclastic flow, or cloud, a fast-moving body of shrieking-hot gases and various materials ejected from the volcano that travels away from it upon eruption.

Normally travelling at a comparatively leisurely 60mph and travel a few kilometers from the base of the volcano. The flow from a supervolcano can easily reach half the speed of sound and travel over 100 miles, annihilating everything in their path.

Pyroclastic flows are incredibly lethal and incinerate, instantly, any living organism they reach. Trees and buildings will be flattened. All the evidence you need of their destructive effect can be seen in the remains of Pompeii and Herculaneum, destroyed by Mt. Vesuvius, and St. Pierre, destroyed utterly by Mt. Pelee.

The danger is far from over. Any air-breathing animal or machine will risk suffocation or illness at the least from inhalation of the enormous quantities of ash and toxic gases. Water supplies will be rendered unable to support aquatic life in no time. Machines will be affected by the amount of ash that gets pulled into engine intakes and precise fittings.

Satellite and radio communications will be affected as the atmosphere is occluded with fine particulate. Even landlines will degrade or fail, above ground or not.

It does not take much imagination to understand how well a telephone pole would fare against a pyroclastic flow travelling at a significant fraction of the speed of sound, and underground lines are likely to be disrupted by tumultuous seismic activityThe resulting strain and collapse of society and infrastructure will be near total the closer one is to the site of the eruption.

This will not be a bang-pow-flames event; Yellowstone and all supervolcanoes like it are truly cataclysmic in nature.

Can you Truly Prepare for a Supervolcano Eruption?

Preparing for and staying abreast of volcanic eruptions can be tricky. On the one hand, most volcanoes have a sort of rhythm and pace to their activity that is measureable and constantly observed by scientists and other interested agencies. Much of the time an eruption will be heralded by other seismic and geological phenomena, and warnings or cautionary statements will be issued by the Volcano Notification Service.

On the other hand, sometimes a volcano can erupt, even catastrophically, with effectively no warning, allowing no time for effective evacuation. While a smaller volcano could still be survivable, if you are anywhere near the Yellowstone caldera when it touches off you are probably toast, very literally. Early warning would be your only true defense.

If you live near a volcano, or anywhere in the region around a supervolcano, sign up for local and federal warning systems. These notification systems work much like traditional severe weather alerts and status updates, alerting you to increased risk or imminent eruptions. You can get on the VNS here.

The biggest issue with preparing to deal with a supervolcano eruption is its massive range of effect; you could potentially need to flee hundreds of miles just to outside the primary danger area of pyroclastic flow and immense ash and vapor buildup.

Wherever you live in relation to a volcano, you must investigate the risks to your locale based on the particulars of a given eruption. Depending on the type and strength of the eruption your best plan may be to shelter in place, or it might be to flee along a specific route prior to the event should you get enough warning.

Volcanoes are nowhere near as predictable in timing or effect as other disasters; the volcano itself as a feature of the landscape is just one component of a system.

That system is made up of underground chambers of magma under immense pressures from tectonic plates and other geologic action being forced up through conduits into breaches in the earth’s outer crust, the visible mounds and apertures being our volcano itself.

Even the best scientists are comparing data deduced from timescales so long and forces and variables so great that it is, necessarily, and inexact science. This means you can never be 100% certain of when an eruption may occur or how bad it will be.

Procedures for Surviving a Volcanic Eruption

While a volcanic eruption itself produces threats to life that are extreme, both in speed and lethality, they are not the only problem you’ll have to contend with; the aftermath will have significant to severe impact on all aspects of society for the foreseeable future.

The impact on the environment will lead to shortages or drastically increased prices of food, water contamination, significant temperature shift and probable issues with travel depending on the area directly affected and air quality issues (aircraft never work well with engines full of ash). Economic backlash will likely be significant also, so that is another issue to be prepared for.

The U.S. government has detailed, step-by-step procedures for escaping or avoiding danger posed by volcanoes. I have reproduced those steps here with my own commentary. With a little luck and warning, if you act quickly enough and can get far enough away from the volcano prior to the big bang your chances of survival are good.

Pre-Event Preparation

Know Your Local Risk from an Eruption: Not all areas will be impacted equally, even near a volcano. If you live in a high-risk area, you must take extra precautions.

Investigate Evacuation and Shelter Plans Early: In some areas there may be suitable shelter for protection against the worst of a volcanoes deadly effects. Talk to local emergency management officials to find out more, as they may not be easy to find.

Be Sure to Activate Early Warning Notifications: It cannot be oversold how important early warning is for surviving a volcanic eruption, especially a supervolcano.

Stock Needed Supplies and Equipment in Advance: This is as fundamental as it gets for preppers. It will be way too late to get or gather what you need when the smoke starts rising. Hit all your essentials here- food, water, medicine, lighting, personal docs, etc. Double-stock fire extinguishers: flying debris will likely be exceedingly hot, and will readily set fires.

Consult Physician about any Breathing Ailments: A volcanic eruption will be doubly hard to manage if you have any kind of persistent breathing difficulty or lung disease. Consult your doctor and explain your concerns. See if there is any additional precaution you may need to take to deal with toxic vapor or ash, even in small concentrations.

Create and Practice Communications and Evacuation Plans- You may have little warning of a volcanic eruption. You will need clear, simple, concise and redundant plans for getting you and yours out of harm’s way. No one waits at home for bad things to happen; have plans for collecting or rendezvousing with your family when everyone is at different places.

Active Eruption Procedures

Listen to Alert Status Updates: The VNS will provide up-to-the-minute info across multiple channels. You should be listening at all times for important updates so you can plan or act accordingly to the situation.

Follow Evacuation Orders: Don’t take them lightly! If a volcano goes big, it is far too late to react. Your only hope is to be far enough away that you survive. Any watch or caution status placed on a supervolcano is reason to leave until it is cancelled.

Be Sure You Do Not Travel Downwind or Downstream of the Volcano: The ash and other debris will be guided by wind. Waterways may be converted by the eruption into a lahar, a nightmare mixture of lava, mud and rock that acts like a boiling mudslide, following the path of the waterway. Extremely dangerous.

If Your Primary Threat is Ash, Shelter in Place: Shutdown and close ventilation openings. Seal windows, doors, cracks and crevices.

If Outside, Protect against Ash: Falling ash can irritate skin and severely injure breathing passages, mucous membranes and your eyes. Use a good, well-fitted breathing mask like the N95 or better.

This is one disaster where a gasmask makes good sense. Get a modern, quality model and supplemental filters. Know how to use it, and keep your facial hair very short.

Do Not Drive or Operate Motors When Ash is Falling: Heavy ash fall will choke, stall and seriously damage an engine when it is drawn in through intakes. Keeping it out of machinery is critical to maintaining operability later.

Aftermath Procedures

Reach Out to Family/Friends Using Text Messaging: Phone systems will be degraded or down in the aftermath of the eruption. Save phone calls for emergencies only. Text messaging has a much higher chance of transmitting successfully.

Avoid Contact with Ash and other Volcanic Material: Do not stir up ash or risk secondary contamination. Volcanic strata can remain hot enough to severely burn for many hours.

Take Care to Remove Ash Buildup from Roofs: On the other hand, ash is much heavier than it looks as it piles up, and just like snow can place terrific strain on roofs. If you can do so safely, try to sweep or push it off of the roof of your shelter. Take extra care when walking over it, as it makes surfaces very slick, just like snow.


A supervolcano is one of the most plausible national- or world-scale catastrophes known, and scientists have pinpointed dozens of cataclysmic eruptions all around the world in the past.

Sadly, one of the biggest and most destructive volcanoes on earth is located smack in the middle of the continental U.S. in the form of the Yellowstone caldera. Despite its incalculable power, it too can be survived if you take the right steps and act immediately on any early warning you get.

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1 thought on “Yellowstone Caldera Eruption: What to Expect”

  1. We prep to increase our odds of living. All is subject to chance. If you have a full on bunker complex and suffer a heart attack and die so be it. But to die from something we could prevent with foresight and preparation’s is stark foolishness. Who thinks it’s a good plan to dance in a busy highway? Who thinks it’s a good idea to tell your hungry kid we have nothing to eat because Grub Hub is not working?

    Proverbs 27:12 The Prudent man sees danger and avoids it, the fool presses on and suffers. Much can be learned from daily readings of the book of proverbs. 31 chapters, 31 days in a month? Hummm

    We are born to die. How you live, how you affect others is important. As William Wallace said “All men die , not all men truly live”.

    We need to prep for the physical and the spiritual. The many times I comforted the dying over decades of medical work I have never found a “Proud Atheist”, everybody wanted some knowledge of a kind and merciful God.


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