Last year I wrote a redemptive short story set in the Western United States after an eruption of the Yellowstone volcano--an event modeled on Yellowstone's most recent "mega-colossal" eruption of six-hundred-forty-thousand-years ago. In this story, the Central United States has been smothered under a meter of abrasive volcanic ash, and the world is struggling through the third year of an unbroken volcanic winter. Human civilization continues to limp along only because of the widespread use of space program technology originally developed for permanent settlements on the Moon and Mars.
I read dozens of papers on "super volcanoes" while researching for this story. Of particular interest were articles on the eighteen-or-so super events that have taken place during the past two million years. Of these, one of the most fascinating but frustrating to research was the eruption of Italy's Campi Flegrei.
Most people are aware that the city of Naples is imperiled by its close proximity to Mt. Vesuvius, which destroyed the Roman cities of Pompeii and Herculaneum in AD 79. Not so commonly known is that the city is also located adjacent to Europe's only active super volcano. Around thirty-nine to thirty-five-thousand-years ago, the Campi Flegrei erupted over five hundred cubic kilometers of rhyolitic ash in a caldera-forming event that must have devastated downwind regions in Europe, North Africa, and the Middle East, and lead to a dramatic climatic shift.
This was also the period during which anatomically and behaviorally modern Homo sapiens first entered Europe. At the time the continent was already inhabited by the Neanderthals.
How Europe came to be settled exclusively by modern humans has been a subject of much debate. It's still not known if Homo sapiens out competed, out bred, or directly killed off Homo neanderthalensis, or if they absorbed some of them through interbreeding. So it was frustrating to read about the eruption of Campi Flegrei during this time and to find out there was almost no information about the volcano's impact on the region's hominid populations.
Now, however, there is new evidence in the form of ash layers and tool deposits in Russian caves. These findings suggest that Flegrei's Campanian Ignimbrite super-eruption played an important role in depopulating portions of Europe and clearing the way for the first influx of modern humans.
If true, this would help to make sense of how Homo sapiens were finally able to displace the Neanderthals, as an earlier Neanderthal presence in the Middle East appears to have kept our ancestors bottled up in Africa for tens of thousands of years. When we finally undertook our first successful migration out of our home-continent, it was south along the coastline of the Arabian Peninsula, skirting the areas inhabited by Homo neanderthalensis at the time.
Campi Flegrei is not the first super volcano to have shaped our species. The earlier and far more devastating eruption of Indonesia's Lake Toba around seventy-five-thousand-years ago appears to have nearly exterminated the human race, and may have left survivors in scattered pockets that were isolated for thousands of years. Depending on if and how far humankind had migrated out of Africa at the time, these groups of separated survivors may have been the ancestors of the first distinct racial groups.
In other words, prior to the Toba event it's likely that all humans possessed a single skin color.
Regardless if our species had left Africa or not, the signs of a population bottleneck from this period are written within our genome. When Toba erupted and triggered a years-long volcanic winter, our numbers and those of other mammals such as elephants and lions plummeted. This left the tell-tale genetic signs of gene selections from large populations suddenly suddenly sectioned into small survivor groups.
As an aside, I don't lose sleep fretting over Yellowstone. No one knows if the volcano is currently cooling off or heating up, just as no one knows what the exact saturation states of the magma in the chambers immediately below the park are.
Super volcanoes depend on intrusions of gas-poor basalt lava from below, which then melts the continental crust and forms caches of gas-rich explosive rhyolitic magma--explosive in the frothy sense that a shaken up can of soda has the potential to jet out it's contents if opened. As the Yellowstone hotspot has already generated three caldera forming eruptions at its current location, it is entirely possible that it has exhausted the ability of the bedrock there to produce more gas-saturated rhyolitic magma. In the six hundred thousand years since the last super volcano scale eruption, it has only erupted large quantities of basalt and some gas-poor rhyolitic lava.
Or it may be saturated enough at this very moment for one final colossal event. Even if there is enough saturated and cystalized rhyolitic magma present, we do not understand the mechanism that causes it to shift from a stable state into volatile chain reaction.
The potential super volcano that I am most curious about at present is the steadily swelling Iwo-Jima caldera several hundred of miles off the southern coast of Japan. Within this volcano, the island of Iwo-Jima has been uplifted over one hundred twenty meters (approximately three hundred sixty feet) during the past four hundred years. The location where the US Marines first landed during the famous and bloody assault on the island of Iwo-Jima is now twenty meters (sixty feet) above sea level.
Further reading for those who are interested:
* Volcanism and the Mantle, Campi Flegrei. This research paper contains maps and photos of the half-submerged Italian caldera's geology and placement.
The present-day Campi Flegrei is of particular interest not only because it is inhabited, but also due to its restlessness. During the 1970s portions of the caldera floor rose by two meters (six feet), and another 1.8 meters of uplift during the early 80s resulted in the temporary evacuation of twenty-thousand townspeople. Europe's youngest mountain also stands at the center of the caldera, erected there during an eruptive period in the 1500s.
* Monitoring super-volcanoes: geophysical and geochemical signals at Yellowstone and other large caldera systems. A previously cited, easy-to-read and very informative Royal Society paper on Yellowstone and the difficulties in monitoring known super voclanoes to determine if a large-scale eruption is imminent. Also includes is a clear history and good maps of past activity.
* Radiating Volcanic Migrations: An example from the Pacific Northwest, U.S.A.. A research paper detailing how the emergence of the Yellowstone hotpot on the Nevada-Oregon border accompanied a transformation that radically altered the shape of much of Western North America. Good maps of major associated volcanic activity and the volcano's migration on page three, four, and five.
The video below shows the stretching and thinning of the Western United States' continental crust driven by its collision with the northward moving Pacific plate. This collision and stretching first began shortly--in a geologic sense--before the Yellowstone hot spot first emerged. Interestingly, both the Yellowstone and Newberry volcanic hotspots as well as the chain of rifts that buried much of the Pacific Northwest under layers of basalt lava all appeared at the center point of this stretch over a two million year period.
* Mantel Plumes.org. A site with articles written by geologists debating the existence of mantel plumes. Some scientists believe that Yellowstone and other volcanoes that have persisted for millions of years are the products of heat plumes rising from deep within the Earth's mantel. Others believe that these are localized hot spots formed by interactions between the upper lithospheric layer and the mantel beneath it.
* The fate of the Juan de Fuca plate: Implications for a
Yellowstone plume head. The Pacific Northwest region of United States and Southern Canada is currently overriding an oceanic plate that is subducting beneath the North American continent. In this journal article, two geologist argue that they have empirical evidence that suggests that the subducted oceanic plate beneath Eastern Oregon was destroyed by the arrival of the Yellowstone plume, seventeen million years ago.
* Upper-mantle origin of the Yellowstone hotspot. A research a paper written by two USGS scientists and a University of Durham professor arguing that there is no empirical data for a mantel plume beneath Yellowstone.