: The greatest volcanic eruption about which we know quite a lot Toba, Indonesia
The naysayer of our time are busy telling us that increases of carbon dioxide in the atmosphere will destroy human life and our cities before the end of this century unless we change our ways and reduce the present levels of carbon dioxide. Yet, beneath our feet are forces of change far more destructive for the earth’s environment and all of its occupants than anything that human activity has done or can ever do.
Ordinary volcanic activity is familiar to us because we see it frequently. It is no surprise to visitors in
when magma pours on to the surface from deep volcanic vents. It is a common occurrence. Occasionally, however, a super volcanic eruption occurs—one that affects the entire globe. Fortunately, they appear rarely in human history but their destructive power is enormous and, unfortunately, their timing is not predictable. We give the name super volcanoes to them. Toba was one of these, the biggest of all of them within the last two million years with a Volcanic Explosivity Index (VEI) of 8. It is now the model by which geologists assess worst-case scenarios for the future. Hawaii
There are only about half a dozen locations around the world where geologists have identified supervolcanoes.
One location is in
New Zealand, one in Japan, and one in . In the Russia United States there is one in where there was an eruption of strength 8 on the VEI, about 640,000 years ago. That strength represents a tenth of Toba’s and a hundred times the strength of Yellowstone National Park Krakatau.
The past geological history of
Yellowstone reveals that it builds up to the level of a super volcanic eruption approximately every 600,000 years so it is reasonable to say, as some geologists have already said, that another terrible explosion is overdue. Geological specialists have been checking the movement of magma deep below . Yellowstone Park
The presence of this magma is well known by the surface manifestations of boiling
and mud pots. hot springs
Precise measurements over time show that the land within the caldera that is now
Yellowstone rose thirty-five inches between 1923 and 1984.
Later in the 1980s it subsided slightly.
Yellowstone eruption on the scale of the previous one is a terrifying concept. It would transform all aspects of human life worldwide. The death toll would be huge. Although its VEI would only be one-tenth that of Toba, it would be disastrous. Tambora, an Indonesian volcanic eruption of 1815, was ten times stronger than Krakatau and only a tenth as strong as the ancient Yellowstone one yet it caused widespread destruction of life and agriculture all over the world. If no one wants to see a repeat of the ancient Yellowstone eruption, then it is even more certain that we do not want to see another Toba, especially since the scale of its destructive activity is now known through seafloor cores and ice cores from Greenland. From both of these data banks we can define climatic conditions around the time of Toba’s eruption. Overall it is clear that the dust cloud from the explosion, one that reached high into the atmosphere because it happened near the equator, reduced the amount of sunshine that could reach the earth. Thus, temperatures worldwide were lowered by as much as seven degrees Fahrenheit and this condition remained for more than seven years. Had the eruption occurred near the North Pole the atmospheric dust would have stayed at a lower level within the atmosphere
It is tempting to think that once the seven or more years had passed everything would come back to its former state.
The reality was quite different. To begin with, the eruption coincided with one of the last phases of the last Ice Age, the Wisconsin Ice Age. The years of lower temperatures were an addition to the influences that ice was already exerting on the environment. Overall, geologists concluded that the damage caused by Toba was similar to the scenario drawn up by scientists for the effects of a nuclear war, generally described as nuclear winter. The aftermath of this global environmental disaster was most severe in tropical areas where vegetation is unprepared for coldness. In these tropical areas all the plant tissues above ground would die. Even temperate forests would suffer from the relatively sudden drop in temperatures and 50 percent of them would die.
Large amounts of dead wood, aided by drought, typical of ice age regimes, would likely lead to an increase in forest fires.
The story would be similarly destructive for life in the oceans but the elements involved would be different.
Geneticists believe that Toba had a particularly catastrophic effect on humans who, 74,000 years ago, were still at an early stage of development.
The population on Earth may have been reduced to a few thousand people, pushing humanity to the edge of extinction. Homo sapiens had become an endangered species. The evidence for the catastrophic reduction of numbers around the time of Toba comes from an analysis of mitochondrial DNA that revealed a limited genetic diversity, far lower than the known age of humans would indicate. The total numbers of humans in the years following Toba seemed to be no more than ten thousand. Not until 50,000 years ago, 20,000 years after Toba, was there evidence of a rapid and widespread increase in the numbers of humans. In order to test the validity of their calculations regarding humans, geneticists examined the mitochondrial DNA of chimpanzees to find out if they too had been victims of the same environmental disaster. The results were conclusive.
They had experienced a bottleneck similar to human DNA.