The Volcanic Explosivity Index or VEI was created in 1982 to describe the magnitude of explosive volcanic eruption in much the same way that the Richter scale describes the magnitude of earthquakes. 0 is the lowest rating and 8 is the highest. Mt. ST. Helens, for example, is a category 5 on the VEI. This means it ejected at least a cubic kilometer of substances like ash, pumice and lava and belched forth a plume of gas and dust reaching at least 25 kilometers into the atmosphere. To reach super volcano status requires a full blown category 8 eruption, an explosive event which again sends a plume 25 kilometers into the atmosphere but ejects at least 1000 cubic kilometers, or 240 cubic miles of ejecta.
The last known super volcano eruption took place about 71,000 years ago, the Toba event, originating on the Island of Sumatra. The eruption had profound climatic impact precipitating a drop in temperature of 9 degrees F in equatorial areas and as much as 27 F in higher latitudes. This triggered a 6 year long volcanic winter and a thousand year long ice age. There is profound debate on the impact on human development and evolution; one school of thought holds that humankind, represented by both Erectus and Neanderthalus were reduced to a total population as low as 10,000 worldwide, others maintain that the impact was marginal.
Super volcanic trouble spots:
Are there volcanic hotspots around the globe today that have the potential to erupt with the shattering force of a super volcano? Yes, there are in fact at least six, and they have at various times in the past exploded with devastating consequences to planetary climate and habitability.
This list of potential trouble makers – if we wish to define the possible end of all life on earth as trouble – begins with a familiar name, that of Toba caldera on the Indonesian island of Sumatra. Although the area is for now generally stable the magma dome that generated the titanic eruption of 71,000 years ago is very much in place, and remains a seismically active zone, indicating that all, long term, may not be well in Sumatra.
New Zealand has its own claim to cataclysm, the vast and scenic Taupo caldera on the North Island. Just 22,600 years – an eye blink in geologic time – ejected nearly 1200 cubic kilometers of volcanic material. A mere 1800 years ago a relatively minor eruption buried 20, 000 acres under a layer of ignimbrite. The area remains active, potentially dangerous and therefore closely monitored.
The Aira Caldera in Japan, the Valles caldera complex in the United State’s New Mexico and a huge portion of Yellowstone Park, which comprises much of western Wyoming and portions of Idaho and Montana as well are all the scenes of super volcano type explosions in the past; Yellowstone is particularly notorious for no less than 3 known major eruptions, the last one taking place about 600,000 years ago. One titanic Yellowstone blast which occurred just about 2.1 million years ago ejected an almost unimaginable 585 cubic miles of material and formed a gigantic caldera over 60 miles in diameter.
If an event of that magnitude, if it occurred today, would kill nearly everyone and every thing in the United States and much of Canada and Mexico as well. There would be profound and generally lethal consequences for nearly every region on earth. It is not a pleasant prospect on which to dwell, and yet the BBC and discovery channels have recently done just that, producing extremely informative documentaries on the subject of a Yellowstone super eruption.
And yet, the Yellowstone caldera does not appear to be our biggest threat in terms of cataclysmic volcanism. Seismically active, yes indeed the Park is famous for just exactly that. A strong track record of previous eruptions, the geologic record clearly records that very thing. But not an imminently dangerous hot spot, if we are to believe the experts.
That honor may go to the Long Valley caldera in California, itself the location of a large magma dome and with a record of cataclysmic eruption. But more importantly, there is evidence that the Long Valley caldera is rising, that the magma dome deep below may be rising inexorably to the surface. This makes Long Valley the hottest of the known hot spots, and is closely monitored by a number of scientific institutions.
A big bang theory:
What would happen if a super volcano erupted tomorrow? Let’s use the example of the aforementioned Long Valley Caldera; and postulate an eruption of ten days duration ejecting perhaps 2000 cubic kilometers of material.
The result for most inhabitants of California and adjoining states and provinces of Mexico would be death, by shockwave, by superheated air, by burial under hot ash, by suffocation by highly sulfur charged air, and by “lava bombs” chunks of magma thrown many, many miles. Those unlucky enough to survive the initial explosion would surely die of starvation, and respiratory failure. Volcanic ash can be survived when the exposure is minor, but these folks would have to way to mitigate its effects, relief efforts would not be possible except perhaps, at the very edge of the ash field. Animal and plant life would be similarly scoured from the field.
But the effects would be far more widespread: In several weeks the entire globe would suffer a nuclear type winter due to the tremendous quantities of nearly aerosolized volcanic ash and the incalculable tons of sulfur and other volcanic gases. Global cooling of 10 degrees or more on average, with dire consequences for agriculture would be inevitable. An instant ice age of a thousand years or more would be inevitable. If humans survived at all the consequences for social order would be grim indeed.
Don’t book passage to the moon just yet:
Another super volcanic event is inevitable, but even the relatively dangerous Long valley hot spot is unlikely to erupt next year, or next century, or even within the next 10,000 years. For now, mankind has far more imminent dangers to contend with; and the super volcano as presented in the form of disaster fiction may simply function as an escape from those more pressing dangers.
