Deep beneath the surface of the earth, two supervolcanoes of unimaginable ferocity lie dormant in the American states of California and Wyoming. If they explode, then in a matter of hours the entire western part of the United States will be covered with a thick layer of volcanic dust. Each of these volcanoes has exploded at least four times in the past two million years! Fire-breathing monsters of similar power await their time in the depths of Indonesia and New Zealand.
The countdown has begun
The eruption of a supervolcano in destructive power can only be compared with the fall of a medium-sized asteroid. But this monster wakes up ten times more often - about once every several hundred thousand years - and gives rise to the most dramatic natural disaster that could befall humanity. Moreover, in addition to the momentary consequences of this tragic event, remote, for example, unpredictable changes in the global climate will also occur. It is not surprising, therefore, the great desire of researchers to understand the reasons for this phenomenon, so that if not to prevent this deadly cataclysm, which, of course, people cannot do, then at least to foresee it. Scientists have been dealing with this problem since the 1950s, but only in recent decades has there been a tangible breakthrough in understanding the mechanisms operating inside supervolcanoes.
Calderas
The word “caldera” comes from the Spanish caldera, which means “big cauldron,” and refers to an oval or circular depression at the top of a volcano, usually formed after an eruption. There are calderas 30-60 kilometers in size and several kilometers deep. They tend to arise when underground voids beneath volcanoes (volcanologists call them magma chambers) overflow, and high-pressure magma breaks through vents "plugged" by solidified rock masses. And there is an explosion! The aforementioned enormous calderas were generated by true supervolcanoes, hundreds and thousands of times larger than those known to scientists! It is clear that the magma chambers under these calderas were monstrous in size.
Yellowstone National Park is home to three relatively young calderas of supervolcanoes. They were formed at different times - 640 thousand years ago, 1.3 million and 2.1 million years ago.
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Magma chambers
Over the past two million years, four supervolcanoes in the areas of Yellowstone National Park in Wyoming, Long Valley in California, Toba in Sumatra and Taupo in New Zealand have ejected 750 cubic kilometers of magma from the bowels of our planet!
Since the mid-1970s, studies have been conducted on the peculiarities of the formation of magma chambers. Super-eruptions occur as a result of the appearance of vertical cracks under the influence of magma pressure, reaching the Earth's surface. Magma rises along these cracks, multiplying their number in a circle. A kind of ring is formed, inside which a massive cylinder is formed, devoid of support. It collapses into the empty magma chamber, like the roof of a house that has lost its walls! This collapse squeezes out the remaining magma and gases in the chamber, rushing into the annular vents.
Tiny crystals will solve the big problem
It has long been observed that chunks of volcanic rock are composed of tiny crystals. However, only by the end of the 1980s did it become possible to begin a more thorough study of them. In the last decade, geochemists have become seriously interested in crystals of the zircon mineral, which are part of volcanic rocks. The mineral attracted their attention with its high resistance to high temperatures and pressure. It turned out that zircon crystals contain oxygen-18, which has not 8 neutrons in the atomic nucleus, as in atmospheric oxygen, but 10! In addition, in the studied samples of zircon crystals, there was little oxygen isotope - less than in magma! This meant that the zircon was formed from rocks washed by rain or crumbling snow!Based on the study of zircon crystals, geochemists were able to work out a method for assessing the likelihood of impending supervolcano eruptions. True, different opinions are expressed about the interpretation of the estimates made. At least some geochemists predict the imminent onset of a new cycle of volcanism.
Disagreements arose over the consequences of the super-eruptions. The explosive nature of the release of magma from the magma chambers is determined by two factors - the viscosity of this substance, that is, the rate of its outflow, and the pressure difference in the magma chamber and on the earth's surface. To test this assumption, special studies were performed. Studied, in particular, the nature of the outflow of magma at the microscopic level.
Consequences of super-eruptions
Several models of these processes were considered. In one version, a large-scale eruption of supervolcanoes in Long Valley and Yellowstone National Park was simulated under the condition of superheating of ash and gases, which in this case would rush into the upper layers of the stratosphere to a height of 50 kilometers. As the "roof" over the magma chamber collapses, huge gray clouds erupting from the vent will scatter horizontally around the caldera. These flows, which are intermediate formations between lava and ash, will spread extremely rapidly - at speeds up to 400 kilometers per hour! Cars and even light aircraft will not be able to "escape" from them. In addition, streams of gray clouds will be very hot - up to a temperature of 600-700 degrees Celsius.
This means that they will incinerate everything around within a radius of tens of kilometers. The gray clouds mentioned above will leave even more ominous and far-reaching consequences.
In an area hundreds of kilometers around the supervolcano, lumps of white-gray ash will fall out for several days or even weeks. Even within 300 kilometers, the thickness of the fallen ash will be at least half a meter. If it mixes with rain, wet and therefore heavy ash will collapse rooftops on many residential buildings. Within a radius of 200 kilometers around the caldera, even at noon it will be as dark as twilight. In addition to what has been said, we will mention power failures in cities, ash clogging of navigable rivers, irreparable damage to agriculture.
Another factor is sulfuric acid
Of the many gases emitted by volcanoes, sulfur dioxide is particularly harmful to the environment. Reacts with atmospheric oxygen and water, it forms droplets of extremely toxic sulfuric acid. It is these droplets that block the sunlight, turning day into night and "providing" our planet with a cold snap. This situation is becoming similar to the notorious "nuclear winter", predicted as the disastrous outcome of nuclear war. The peculiarity of hydrological cycles on Earth is such that self-cleaning of the planet from the consequences of supervolcanic eruptions will take decades! Interestingly, in 1996, glaciologists examined samples of ice cover from Greenland and Antarctica and found traces of sulfuric acid there in layers corresponding in time to the eruption of the Toba volcano in Sumatra, which occurred 74 thousand years ago!Then from the bowels of the planet, 2800 cubic kilometers of lava and ash were expelled, and the global air temperature dropped on average by 5-15 degrees Celsius! By the way, the researchers found that the bulk of the sulfuric acid evaporated from the ice in six years!
Let's not forget about ozone
Geochemists conducted a special study of a particularly effective oxidant - ozone. It is a gas that protects all life on earth from the harmful ultraviolet radiation of the sun. When ozone in the stratosphere interacts with sulfur dioxide, acid is formed, which falls to the ground with rain. Here she interacts with volcanic ash. Thus, a thinning of the protective ozone layer occurs.
As a result of the 1991 eruption of Mount Pinatubo in the Philippines, the protective ozone layer in the atmosphere was thinned by 3-8 percent!
Magazine: Secrets of the 20th century №22. Author: Leonid Prozorov