Are there any supervolcanos within China or Mexico?

Question

If it blew up tomorrow, would there be a big populated city nearby?

What percentage of the total Chinese/Mexican population would be directly affected by ...

1. The lava,

2. A tsunami,

3. A pyroclastic flow,

4. The ashcloud,

5. The earthquakes,

6. The fires,

7. Sudden population migration ?

Answer 1

Eruptions with a Volcanic Explosivity Index of 8 (VEI-8) are mega-colossal events that extrude at least 1000 km³ of magma and pyroclastic material. Such an eruption would erase virtually all life within a radius of hundreds of kilometers from the eruption, and entire continental regions further out can be buried meters deep in ash. VEI-8 eruptions are so powerful that they form circular calderas rather than mountains because the downward collapse of land at the eruption site fills emptied space in the magma chamber beneath. The caldera can remain for millions of years after all volcanic activity at the site has ceased.

VEI-8 volcanic events have included eruptions at the following locations

Aira Caldera, Kyūshū, Japan

Aso, Kyūshū, Japan

Campi Flegrei, Campania, Italy

Kikai Caldera, Ryūkyū Islands, Japan

Long Valley Caldera, California, United States

Lake Taupo, North Island, New Zealand

Lake Toba, Sumatra, Indonesia (2,800 km³)

Valle Grande, New Mexico, United States

Yellowstone Caldera, Wyoming, United States

La Garita Caldera, Colorado, United States

The most recent VEI-8 eruption was at Lake Toba, Sumatra (the Toba event), and occurred around 74,000 years ago, plunging the Earth into a volcanic winter and quite possibly threatening the existence of Homo Sapiens, resulting in an estimated 40% death of our ancestors and resulting in the remaining population numbering as little as 14,000 individuals, thus creating a bottleneck in our evolution that is evident in our lack of diversity in our mitochondrial DNA.

The largest known eruption on Earth occurred at the La Garita caldera in the San Juan Mountains approximately 28 million years ago.

There are a few of these volcanos that are near to your selected countires, namely those in the Southern USA for Mexico, and those in Japan for China.  But most of your follow up questions are impossible to know.  The Japanese volcanos may pose the risk of Tsunami's that could ravish the Chinese coast, the ashflow would go with the prevailing winds and thus would flow away from both of your questions in question (the majority of the ashcloud would go towards the east seeing as the US and Japan are in the Northern Hemisphere, not south as would be needed to effect Mexico immediately, or west to effect China immediately.)  Fires would pretty much be irrelivent in the effected regions in the immediate aftermath.  Some migration might occur in the regions form thousands of kilometers away where the first survivors might be found, but also don't forget that as the cloud spreads around the globe all areas will eventually be affected and airtravel will probably become impossible because of the sulphuric acid and ash in the air.  The distance that would have to be covered to escape the worst effected area would be difficult to acomplish so I think that people would just be forced to sit tight and die from ash/acid inhalation eventually if they were close enough to be affected that badly.  The survivors of such a catastrophe would now be living in a drastically altered world.  It would be much cooler as less sun would reach the earth for many thousands of years and an ice age would follow, which is actually a good thing because the snow fall and compression into ice would store some of the pollutants and clense the atmosphere slowly.  We would have to adapt to discovering new sustainable food sources, and many that were not even close to the eruption would starve to death over that adaption cycle.  In human history we have altered our environments to survive, but in this case it would not be that simple, because it would be our food supply that was under threat, not our ability to protect ourselves from the harshness of this new environment.

Answer 2

No and none but there are volcanoes.  Supervolcanoes generally refers to very ones with very viscous magma like yellowstone.

Answer 3

There was one in Liaoning province, another in Guizhou province, another in Australia. But not sure about Mexico.

As for the effects on the local populations, I can tell you from my experience in fossils remains, that the population don't even have time to react, death is almost instantaneous after the explosion, since it is so huge.

I find fossils of Psittacosaurus still standing, others sleeping. While in Guizhou, most trapped animals were aquatics, and also get trapped while swimming...

Even one of my friend got a specimen with his prey still half in his mouth...

So, if you know about supervolcanos, you should also know, that its not its local effects that will be the most disturbing, but its global effects... At your place, I would investigate those before looking to the local effects.

And by the way, the beast that got killed in the eruption, were not killed by the lava, nor a tsunami, but by the ashclouds!! They just got litterally covered with it, in a fraction of a second suffocating them almost instantly!!

Answer 4

Well, if a Super Volcano erupted in either of those countries the entire population would be affected.  However, they don't know where all of the Supervolcanoes are in the world.  Some are only known because of the amount of ash that was dumped over a large region, but they have yet to locate even some of those.

Toba is in Sumatra, Indonesia (which is kind of in one of those areas).  It has a 1,080 square mile caldera and last erupted about 74,000 years ago (with a bigger eruption than Yellowstone).  It wiped out enough of the world's population to distort the results of genetic studies of human origins.  I don't remember what they said the spread was on the ash, but the ash made the Earth cool down very rapidly worldwide.  They can only guess at what an eruption like that would do to fault lines, oceans and more.

The Sibarian Traps had lava flows that spanned the size of the United States, but there doesn't seem to be any activity there now.

The other close one to China is Aira.  It is only 150 square miles.  This one seems to be somewhat active, but is mostly venting through smaller volcanoes that have formed within it.

The Valles Caldera in New Mexico is the closest to Mexico that they are aware of.  It is still very mildly active with it's hot springs.  It through ash as far away as Iowa.  

Some of this was from memory, but my source for filling in the blanks I couldn't remember is seen below.  I would say that certainly all of either of those countries would be directly affected by a supervolcano should one decide to become known.  However, it would be felt worldwide.