There is nothing to suggest that any ancient civilization would have been able to predict volcanic eruptions thousands of years hence. Therefore the inclusion of this section is due to super-volcanoes fitting the global cataclysm category, and because we shouldn't rule out any possibilities, no matter how remote. Also, keep in mind that a pole shift type event might be predictable, and a pole shift could be the trigger for an eruption - so they don't necessarily happen in their own due course.
In general, if a global cataclysm triggers volcanic eruptions, active volcanoes presently exist on every continent except for Australia. But the type of volcano that can single-handedly harm the entire planet in a substantial manner is a super volcano.
What is a Supervolcano?
A supervolcano is an arbitrary definition for volcanoes that can have the largest of eruptions. It is such a recent term, the spelling of the word is not yet set in concrete, but we'll use the spelling most commonly used. While there is no precise measurement used to qualify a volcano as "super", the word is used to describe a volcano that can threaten global civilization. A supervolcano will either wipe out all of humankind, or make a very good attempt to do so.
It is the only local, natural event that has such power, and ranks alongside comets and asteroids as a force of nature we should fear.
Supervolcanoes tend to be active over millions of years. They erupt less frequently than other volcanoes, but when they do erupt, they are substantially more intense. They are rare enough to be missing from modern history, and we only know they have ever occured due to geological studies of the clues they have left for us.
Supervolcanoes of the Past
These are the largest supereruptions we are aware of - they all have a Volcanic Explosivity Index of 8 (VEI-8) which means they have thrown out at least 1,000 km³ Dense Rock Equivalent of ejecta. The level of ejecta is the most important criteria in terms of risk to the survival of our species. Local disasters will not affect our continued existence, but this level of ash in the atmosphere will create immense difficulties for the entire planet.
26,500 years ago - Lake Taupo, NZ - 1,170 km³
74,000 years ago - Lake Toba, Sumatra - 2,800 km³
254,000 years ago - Whakamaru, NZ - 1,200-2,000 km³
640,000 years ago - Yellowstone, USA - 1,000 km³
2.1 million years ago - Yellowstone, USA - 2,500 km³
2.5 million years ago - Cerro Galan, Argentina - 1,050 km³
4 million years ago - Atana Ignimbrite, Chile - 2,500 km³
4.5 million years ago - Yellowstone, USA - 1,800 km³
6.6 million years ago - Yellowstone, USA - 1,500 km³
27.8 million years ago - La Garita Caldera, USA - 5,000 km³
29.5 million years ago - Sam Ignimbrite, Yemen - 5,550 km³
As an indication of how massive these supereruptions were, Mt St Helens had just 1.2 km³ of ejecta, and Krakatoa had 25km³.
While it might be possible to discern eruption patterns for individual volcanoes, collectively it becomes much more random. Hopefully scientists will be able to forewarn us of the next one to blow.
How Bad Can a Supervolcano Be?
The supereruption of Toba caused temperatures to drop globally by between 3 and 9 degrees Farenheit, as much as 18 degrees in some places, killed 80-90% of humans and destroyed as much as three-quarters of all vegetation in the Northern Hemisphere. (1) Substantial amounts of ash were distributed across southern Asia. In India, the ash was typically six inches thick, and at one site it reached an extraordinary depth of twenty feet (2).
Tephra is the fragmental material created by a volcanic eruption. Different types of tephra are determined by size - anything larger than 2.5 centimetres is called a "bomb", and ash is the smallest. Volcanic ash is quite different to the ash you get from burining something. Because it is a fragment of glass or rock, it has sharp edges - if you breathe it in, you will damage your lungs. These tiny pieces will combine with the moisture in your lungs and form a type of cement.
The eruption of Mount Tambora in 1815 was minor compared to a supereruption, but serves as an example of the types of problems we could face. It ejected an estimated 36 cubic miles of ash and pumice, rising as much as 30 miles into the stratosphere. This cloud drifted around the world, visually affecting the atmosphere above both Europe and the USA. Many places suffered their worst winter on record. The winter at Yale University, in Connecticut USA, was 7°F below average. In Europe, food shortages were commonplace. Riots broke out, and armed groups looted farms. Ireland was worst hit, where the famine was believe to cause the spread of typhus, infecting 1.5 million people and killing 65,000. It was known as the Year Without Summer. In the last 600 years, only one year has been colder - 1601, following the eruption of a Peruvian volcano.
The famous Krakatoa eruption of 1883 caused a series of tsunamis, up to 100 feet in height, killing tens of thousands of people. The final explosion was defeaning, and was heard 3,000 miles away.
Research into some likely large eruptions from 6th century (El Chichon) and 13th century (Proto Krakatoa) suggest that they may have also caused famines, in each case leading to a wipespread plague outbreak, and possibly, in the case of the former, causing the Dark Ages.
Chlorine gases emitted can damage the ozone layer. On top of the damage we have already inflicted via CFCs, the eruption of a supervolcano could deplete the ozone layer to such an extent that it becomes another deadly side-effect. The increase in ultra-violet radiation would cause skin cancer in humans and damage crops.
The excellent Supervolcano, by Dr John Savino & Marie D. Jones, includes an in-depth, fictional account of a Long Valley supereruption. Based on current scientific understandings, it is compelling reading. Here's a brief excerpt:
Within days and weeks of the supereruption, the suspension of air routes, the inability to bring cargo in and out of the most deeply affected areas, and the virtual decimation of the Grain Belt, the area of our nation responsible for the vast majority of our grain food sources, all contribute to a growing sense of desperation and panic among survivors anxious to find food. It only takes 0.04 inches of ash to close airports, and the wide swath of blanketed ash would literally shut down every major and minor airport for thousands of miles across the country.
Because even a small amount of ash can clog an engine, road transportation is heavily curtailed, and trucks and machines normally engaged in the moving of supplies from one state to another find themselves immobilized. Electrical equipment shorts out, and wide areas experience power outages and rolling blackouts, rendering communication via computers and phones obsolete.
The description continues, pointing out the importance of short-wave radios. They tell of food riots and contaminated water, of violence and anarchy. Although the USA is the worst hit, the suffering is global. Greatly decreased food production means mass starvation and social unrest. It is a truly horrific scenario. While we can only hope and pray it does not happen in our lifetime, it will certainly happen one day. It would be extremely unlikely that mankind can ever tame even the smallest of volcanoes, so it would appear that a global catastrophe via a supervolcano is entwined in human destiny.
This map shows the extent of ash fall from the last three eruptions of Yellowstone:
Candidates for a 2012 Eruption
We know of roughly 50 supervolcanoes that have ever existed, and most of those are now extinct. Others are believed to be dormant, while a few are currently active - listed here under their common names:
- Toba (Sumatra, Indonesia) - supereruption 74,000 years ago, which was the largest volcanic eruption anywhere on Earth within the last 25 million years. Most humans did not survive this eruption, and in theory it caused a population bottleneck that may have contributed to our evolution, or at least our genetic makeup. Toba may have been active within the last several hundred years
- Yellowstone (USA) - last erupted 630,000 years ago. It has been speculated that the force of a Yellowstone eruption would be the equivalent of one thousand Hiroshima bombs exploding per second (3)
- Long Valley (California, USA) - last erupted 760,000 years ago (600 km³ of ejecta).
- Valles Caldera (New Mexico, USA) - last erupted 1.15 million years ago (600 km³ of ejecta)
- Lake Taupo (New Zealand) - supereruption just 26,500 years ago. Has erupted roughly every thousand years since, with the most recent, 1,800 years ago, being considered the largest in recorded history, 100x larger than Mt St Helens. Fortunately it was not recorded, for New Zealand was yet to be settled by humans.
- Phlegraean Fields (Naples, Italy) - supererupted 39,000 years ago (500 km³ of ejecta), with other major eruptions since. Could have a major eruption within decades.
Active - but no evidence they are capable of wiping us out
- Kikai Caldera (Japan) - supererupted 6,300 years ago. Still active, with minor eruptions occuring as recently as 2004
- Laacher See (Germany) - potentially still active, erupted 12,900 years ago
- Mount Tambora (Sumbawa, Indonesia) - last erupted in 1815, killing at least 71,000 people.
- Aira (Japan) - erupted 22,000 years ago (400 km³ of ejecta), but is still very active. In 1914 an eruption caused the evacuation of 23,000 people. The city of Kagoshima is very close by.
The Yellowstone caldera is an active place, and there are regular reports that could cause some people to be concerned. Unfortuanately, because we have only been monitoring this area for less than a century, it's impossible to tell whether the current activity is relatively normal, or if it is unusual and an indicator that something is up.
A 25 mile section of the caldera rose 5 inches between 1997 and 2003. Prior to this, the whole caldera has risen, fallen, risen, fallen. Between 1923 and 1975 it rose 3-4 feet. Geysers start and stop mysteriously. In an average year the region has thousands of earthquakes too small for people to feel underneath them.
Paranoid folk might want to keep their eye on the Yellowstone Webcam
Long Valley is rated by the U.S. Geological Survey as a bigger risk than Yellowstone. Magma is bubbling beneath the surface, and strong earthquakes are not uncommon - in 1980 it had four which measured 6 on the Richter Scale. Paoha Island in the neaby Mono Lake was created from an eruption just 350 years ago.
This caldera is also showing signs of unrest. Containing a large portion of the city of Naples, a supereruption similar to the one 39,000 years ago would devestate Europe. Since the late 60s the caldera has risen by 3 metres. Even more worrying, scientists are preparing to drill into the volcano, an act that some experts consider irresponsible, and could result in an eruption.
In early 2010 the Icelandic volcano Eyjafjallajokull caused weeks of travel chaos, due to airlines not willing to risk their engines by flying jets in zones that could be stricken with ash. In the greater scheme of things this is a minor volcano, yet it still manages to grind local air travel to a halt. A supervolcanic eruption would render us completely useless...
Government to the Rescue?
Two years prior to the Mt St Helens eruption of 1980, scientists predicted that an eruption would occur within 22 years. But would such information be made public about an imminent Yellowstone eruption? For example, if a study predicted an eruption in the next 10 years, the economic upheaval created by half of America relocating could be too much to bear. Leaders might choose to ignore the possibility and cross their fingers. Like they (unfortunately) did with New Orleans. Plenty of conspiracy theorists have discussed the possibility of governmental secrecy (at the Above Top Secret forum, the Yellowstone topic has over 600 pages of posts), but of course proof is lacking otherwise it would be fact, not theory.
Where is Safe?
The relative lack of volcanoes make Australia and southern Africa the places to be...
Having said that, Australia may not have any active volcanoes, but it did, and it will. The most recent eruptions occured in South Australia (5,000 years ago), Victoria (10,000 years ago) and Queensland (13,000 years ago). For millions of years the level of activity in Australia has been decreasing, but small eruptions are still likely in the future. See The Volcanic Earth by Lin Sutherland for details and maps of Australian volcanoes. It also includes future scenarios, and predicts that eruptions that could affect us would be small, with the main hazards being lava flow and bushfires. Australian eruptions would be a minor inconvenience compared to the climatic disturbances for Australia coming from supervolcanic eruptions elsewhere.
Some useful, official sites, for monitoring Yellowstone:
- Yellowstone Webcams
- Yellowstone Volcano Observatory
- Frequently asked questions about recent findings at Yellowstone Lake
This official site describes actions to take in an ash fall situation :
And one non-official site with plenty of info:
(1) Supervolcano, by Dr John Savino & Marie D. Jones p37
(2) Supervolcano, by Dr John Savino & Marie D. Jones p123
(3) Supervolcano, by Dr John Savino & Marie D. Jones p37