EDIT: damn, this got me my first gold badge
Here is a useful source, which is itself based off of this. Here is an ancillary source.
WTL;DR: all the damage
TL;DR:
- everything within 80 kilometers utterly deleted to an extent I am incapable of describing
- everything within 125 kilometers is the surface of Mars, unbreathable atmosphere included
- everything within 200 kilometers sees everything from buildings to biospheres collapse
- everything within 300 kilometers is post-apocalyptic
- everything within 800 kilometers is basically post-WW2 Germany
- everything outside of 800 kilometers is basically COVID-19 but ten times worse
ZONE 1: HELL
ESTIMATED ASHFALL: 3 Metres
DISTANCE FROM BLAST: up to 80 KM
MAJOR TOWNS: West Yellowstone, Mammoth
POPULATION: 70,000
POPULATION DISPLACED: 100% (guess why)
COST (2012 DOLLARS): 7.1 billion
Zone 1 is called the 'pyroclastic zone'. Surges of scorching hot gas
and ash (over 400 centigrade) exceeding the speed of sound would spill
from the side of the volano [sic] and could extend up to 100 kilometres out.
It is not survivable.
There used to be an entire building here. Note that its rebar - this is reinforced concrete, i.e. what they build support columns for big buildings and the bulk of the structure of nuclear bunkers out of - has been bent in the direction of the pyroclastic flow, rocks have been embedded in the concrete, it has been sandblasted, and it has been scorched black.
There are various ways that that bending of rebar should impress you. Either:
- the flow blew hard enough to bend rebar
- it got hit with so many rocks, pebbles, and the like that it was slowly "hammered" into that shape over the course of a few minutes
- it was heated so heavily that it could be bent like taffy
- a combination of the above
What's more - if this is were the product of a Yellowstone-derived pyroclastic flow, this would be the second story, as the first story would have been buried in 10 feet of ultra-hot ash.
It's a nuclear blast wave from hell - yes, I mean worse than a normal one - without the radiation. It is unsurvivable. It is a soup of ultraheated gases and rocks moving faster than a jet aircraft. Anyone in this zone is irrevocably dead, do not pass GO, do not collect $200, no saving throw, etc.; if you are not in a far-underground, well-reinforced nuclear bunker with air recyclers and zero connections to the surface, you are fucked, you are dead, and the heat might still cook that bunker anyhow.
It's like Hell throwing up on you. A nuclear weapon is child's play compared to this. Extremophile bacteria might survive this. You went outside with a gas mask well haha dumbass it melted onto your face. Life is impossible.
I cannot overstate how incredibly destructive and lethal this is.
ZONE 2: MOON
ESTIMATED ASHFALL: 1.8 Metres
DISTANCE FROM BLAST: 80-125 KM
MAJOR TOWNS: Bozeman, Cody
POPULATION: 350,000
POPULATION DISPLACED: 95%
COST (2012 DOLLARS): 28 billion
Zone 2 would have to be evacuated completely prior to the eruption.
The very heavy ashfall would collapse all structures. Vegatation
[sic], livestock and aquatic life would die. Power and telephone lines
would break and roads would become completely unusable.
Aside from the folks with easy access to fast transportation, nobody is getting out before ~6 feet of ash destroys everything; if you are not in a nuclear bunker (albeit a less-tough one than for Zone 1), you are dead.
Pretty much paved flat. Everything has been crushed by ash fallout. Ash has a density of, on average, 1,000 kg/m^3, which ups to about 1,500 kg/m^3 as it gets rained on. Breathing outside will be very difficult, due to massive levels of airborne sulfuric acids. A gas mask is mandatory.
The dry bulk density of newly fallen and slightly compacted deposits
ranges from 500 to 1500 kg/m3, whereas the bulk density of wet ash
ranges from 1,000 to 2,000 kg/m3. Distal ashfall deposits most
commonly show slight decreases in bulk density with distance from the
volcanic vent source.
In other words, there is between 1.8 and 2.7 metric tons of ash per square meter in the average portion of this area. That's like having two Mini Coopers dropped onto a space the size of a bath towel. Not really survivable for most forms of life; it's just too thick and there's just too much of it.
Roads and reinforced infrastructure would still exist, but that's about the only thing that wouldn't collapse, and they'd still be buried. A lot of buildings are going down under that much weight. Power lines might survive, especially if undergrounded. Microbes will survive in the long run, as well as the hardiest of insect colonies.
ZONE 3: VERDUN
ESTIMATED ASHFALL: 1 Metre
DISTANCE FROM BLAST: 125-200 KM
MAJOR TOWNS: Idaho Falls
POPULATION: 640,000
POPULATION DISPLACED: 90%
COST (2012 DOLLARS): 225 billion
Zone 3 would have to be evacuated completely prior to the eruption.
The very heavy ashfall would collapse all structures. Vegatation
[sic], livestock and aquatic life would die. Power and telephone lines
would break and roads would become completely unusable.
An irritating copy of the text for Zone 2, to be sure, but an accurate one.
People will have time to flee, but they'd have to flee to survive; if you are not in a reinforced, sealed building with long-term supplies, you are fleeing or dead but don't know it yet. Breathing outside will be very hard. A respirator is mandatory.
This is what ~1 meter of ash looks like.
The collapse of the car and building was likely averted by shoveling ash off of both; in the event of a Yellowstone eruption, imagine this but with 3 feet of ash on top of everything - not just the ground - and the car and the building crushed. I recognize that that this doesn't look as bad as the image below, but I guarantee you it's worse; it just doesn't look that way because it's in a more built-up area. It's the best image I could find.
As you can see, cars are going to have a bad time. It won't be as bad as Zone 2, but it's still going to mess people's shit up. Many things will survive the initial ashfall, but then the rain will come along and double the weight, and they'll be crushed. Biological life and supply chains will die right off the bat. The ecological devastation will still be extreme. Bugs might survive in the long run, and small underground animals - like, the smallest of mice.
ZONE 4: POST-BOMB HIROSHIMA
ESTIMATED ASHFALL: 60 centimeters
DISTANCE FROM BLAST: 200-300 KM
MAJOR TOWNS: Salt Lake City, Boise
POPULATION: 11 million
POPULATION DISPLACED: 80%
COST (2012 DOLLARS): 225 billion
Zone 4 would still see substantial amounts of ashfull [sic]. Any areas
with more than 30 centimetres of ash are under severe risk. The
primary cause of death would be from roofs collapsing due to heavy ash
load, potentially 1 in 3 people would be killed this way. Breathing
outside would be very difficult. The water would be contaminated with
sulphuric acid. The ash would enter air filtration systems causing air
quality problems in structures still standing. There would likely be
no power and very limited transporation [sic], if any at all.
Basically a post-nuclear wasteland, which says a lot about the past three zones; if you aren't a prepper here, you're either dead or fleeing. It's still survivable by biological life, though - the ash is thin enough that burrowers, VERY small land wildlife, and creatures in deep lakes might survive. Breathing outside without mechanical filtration is indeed "very difficult" - but, unlike the previous zones, also possible. A respirator is heavily advised.
60-ish centimeters of ash.
Among the first challenges they faced as they sloshed ashore from a
motorized canoe was the two feet of ash.
As you can see, it's not completely collapsing that shack - note that it's a one-story house; it's just that the nearby trees have collapsed under the weight of ash, giving the illusion that those are treetops. On the other hand, ash is about twice as dense when wet, so rain might actually be what takes out buildings that the ash doesn't.
Life will go on in this part, if incredibly differently. Ash levels are low enough that human habitation might be possible in the long run, and certainly in the short run - it won't take down the vital infrastructure right off the bat, so you'll have the time and resources to shovel yourself out and get ready to dig in for when things eventually start failing.
If you want a post-apocalyptic story, this is the place - the right blend of "survivable" and "catastrophic".
ZONE 5: POST-WW2 GERMANY
ESTIMATED ASHFALL: 15 centimeters
DISTANCE FROM BLAST: 300-800 KM
MAJOR TOWNS: Denver, Portland, Calgary, Seattle, Regina
POPULATION: 34 million
POPULATION DISPLACED: 10%
COST (2012 DOLLARS): 234 billion
Buildings in zone 5 are still at risk of collapse if the roofs are not
immediately cleared of ash. Trees would be severely damaged due to
breaking of branches. Road transport would be halted due to build up
of ash on roads and cars would stop working as air-filters become
clogged. Rail transport and electricity may be cut as wet ash short
circuits signaling systems and sub-stations.
Much more survivable, but there will be serious supply chain and minor societal collapses.
A light blanket of ash; oh, sure, the sky isn't black, but look at the ground.. A respirator is advised, as is a snow shovel. This level of ashfall is more dangerous because it's better at killing crops, not because it's better at killing people (at least, not directly).
Imagine this part as Europe during Zero Hour. Society is technically still around, but things are breaking down. The ecosystem is in bad shape, but it'll bounce back.
ZONE 6: INTRA-COVID-19 USA
ESTIMATED ASHFALL: 1-6 centimeters
DISTANCE FROM BLAST: Beyond 800 KM
MAJOR TOWNS: LA, Dallas, New York, Toronto, Chicago
POPULATION: 190 million
POPULATION DISPLACED: 1%
COST (2012 DOLLARS): 213 billion
Minor damage to buildings in Zone 6 will occur as ash enters, soils
interiors and blocks air conditioning filters. Electricity may be cut
as wet ash causes shorting at sub-stations. This would cause water
supplies to be cut. Roads would need to be cleared to prevent ash from
blocking storm-water systems. Crop damage is possible and livestock
may be affected by lack of feed and contamination of water supplies.
Damage to electrical equipment and machinery is likely.
Bad, but basically normal life with massive inconveniences. Imagine the COVID-19 supply chain shortages blown up 10x.
It's nothing in comparison to Z̵͖̤̜͍̼̐̒̇͊̚ô̴̱̹̆̏͒n̶̞̲͌̓͊̓̚ẻ̷̢͎̝̙ ̶̯̳̂̊̀ͅ1̵̥͝. Wear a facemask, change your filters on a bi-daily basis, and listen to your local disaster control authorities. Ration. Store water in your bathtub. Shrink-wrap electronics if you're not using them.
