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Yellowstone – Super Volcano

Copyright © 2012 All Rights Reserved By Daryl L. Hunter ~ written for and originally published in The Greater Yellowstone Resource Guide

Illustration of internal structure of volcanoAt the heart of Yellowstone’s past, present, and future lies volcanism, the Yellowstone Caldera. The Yellowstone Caldera is one of the largest and most active calderas in the world. Catastrophic eruptions occurred here about 2 million years ago, then 1.2 million years ago, and then 600,000 years a go. The latest eruption spewed out nearly 240 cubic miles of debris. What is now the park’s central portion then collapsed, forming a 28- by 47- mile caldera.  Cataclysmic eruptions ejected huge volumes of rhyolite magma; each eruption formed a caldera and extensive layers of thick pyroclastic-flow deposits. Yellowstone’s caldera is buried by several extensive rhyolite lava flows erupted between 75,000 and 150,000 years ago so it isn’t evident to the eye as are most volcanoes. The magmatic heat of the Yellowstone Caldera powers the park’s famous geysers, hot springs, fumaroles, and mud pots. The spectacular Grand Canyon of the Yellowstone River provides a glimpse of Earth’s interior: its waterfalls highlight the boundaries of lava flows and thermal areas. Rugged mountains flank the park’s volcanic plateau, rewarding both eye and spirit. It is Yellowstone’s caldera that creates the geological wonders of Yellowstone.

The Earth’s crust beneath Yellowstone National Park is still restless and very thin.  Surveys have detected an area in the center of the caldera that rose by as much as 86 centimeters between 1923 and 1984 and then subsided slightly between 1985 and 1989. We do not understand the cause of these ups and downs but guess that they are related to the addition or withdrawal of magma beneath the caldera, or to the changing pressure of the hot groundwater system above Yellowstone’s large magma reservoir.

The occurrence of a super-eruption of the Yellowstone Caldera would have severe environmental effects and has the potential to threaten global civilization. The effects of a super-eruption would be comparable to those predicted for the impact of a 1km-diameter asteroid with the Earth. In fact, super-eruptions are 5-10 times more likely to occur than such an impact.

Diagram Yellowstone hot spot theory
Diagram Yellowstone hot spot theory

The Yellowstone Caldera isn’t the only volcano on the Earth capable of colossal eruptions with global consequences.  Such eruptions are quite frequent on a “geological” timescale, although not one has occurred on Earth in the short time that human civilization has existed.  However as our present civilization depends on global trade and food production, air travel and satellite communications, all of which could be at considerable risk if a super-eruption of one of these volcanoes occurred.

Super-eruptions large enough to cause a global disaster average every 100,000 years.  This means super-eruptions are a significant global threat.  They occur more frequently than impacts of asteroids and comets of comparable damage potential.

“Several of the largest volcanic eruptions of the last few hundred years, such as Tambora (1815), Krakatoa (1883) and Pinatubo (1991) have caused major climatic anomalies in the two to three years after the eruption by creating a cloud of sulphuric acid droplets in the upper atmosphere.  These droplets reflect and absorb sunlight, and absorb heat from the Earth – warming the upper atmosphere and cooling the lower atmosphere.  The global climate system is disturbed, resulting in pronounced, anomalous warming and cooling of different parts of the Earth at different times.

“Super-eruptions are up to hundreds of times larger than these, and their global effects are likely to be much more severe.  An area the size of North America can be devastated, and pronounced deterioration of global climate would be expected for a few years following the eruption.  They could result in the devastation of world agriculture, severe disruption of food supplies, and mass starvation.   No strategies can be envisaged for reducing the power of major volcanic eruptions.

It’s not a question of “if” – it’s a question of when!  As several large volcanoes on Earth are capable of explosive eruptions much bigger than any experienced by humanity over historic time.  The occurrence of a super-eruption would have severe environmental effects and are capable of threatening global civilization.  Events at the smaller scale end of the super-eruption size spectrum are quite common when compared to the frequency of other naturally occurring devastating phenomena such as asteroid impacts.  The effects of a medium scale super-eruption would be similar to those predicted for the impact of a 1 km-diameter asteroid with the Earth, but even super-eruptions of this size are still 5-10 times more likely to occur within the next few thousand years than an impact.

The Yellowstone Caldera averages a super-eruption every 600,000 years and we are over due but the chances of it happening in our time or the time of our immediate progeny is slim to none.


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