Did the Yellowstone Volcanic Eruptions Cause Some Large Mammal Extinctions During the Pleistocene?

Most people visiting Yellowstone National Park don’t realize they are standing over an active supervolcano that will destroy most of western North America the next time it erupts.  Yellowstone National Park is located within 3 volcanic calderas created following 3 supereruptions that occurred during the Pleistocene.    A volcanic caldera forms  when the chamber that held all that hot magma empties and collapses into a crater-like landscape.  The Yellowstone supervolcano erupted 2.1 million years BP; 1.3 million years BP; 640,000 years BP; and will erupt again at some unknown time in the future.  Scientists have no way of determining exactly when this will happen, but the catastrophe will likely destroy the United States as we know it.

Diagram of the Yellowstone Supervolcano.

Diagram of Yellowstone calderas formed following 3 supereruptions and 1 regular eruption.

Map showing how far a major ashfall occurs following supereruptions.  Minor ashfall would occur over a much wider area.

Scientists are unsure how the Yellowstone supervolcano originated, but they do know it’s a magma hotspot that has been in existence for 18 million years.  It originally was located in what today is western Idaho, and as the continental plate moved west over this hot spot, its location has been shifting east-northeast so that now it is in northwestern Wyoming.  Actually, the hot spot has stayed in the same place–it’s the continent that has been moving.  There have been 142 caldera forming eruptions from the Yellowstone supervolcano, including 12 supereruptions.  One supereruption occurred 10 million years ago and a foot of volcanic ash fell over a 1000 square mile radius.  The volcanic ashfall preserved one of the best Miocene fossil sites in the world–the Ashfall Fossil Beds in Nebraska.

Inside the rhino house at the Ashfall Fossil Beds Historical Site.

The ashfall from this supereruption preserved over 200 skeletons from 17 species including 5 kinds of horses, 3 kinds of camels, the hippo-like rhino (Teleoceras major), a saber-toothed deer, a raccoon dog, a fox-like canid, secretary birds, crowned cranes, a rail, giant tortoises, and a mud turtle.  Gnaw marks on some of the bones are evidence the bone-eating dog (Borophagus diversidens) was a common predator in Nebraska during the Miocene. The large mammals survived the initial ashfall but died within 3 weeks from breathing volcanic ash.  Volcanic ash consists of tiny shards of glass that eventually destroy lungs.

The 3 Yellowstone supereruptions of the Pleistocene must have caused the extinctions of vertebrate and plant species that had a strictly western distrubution.  Nevertheless, I haven’t been able to find enough information in the scientific literature to link corresponding extinctions with the 3 dates of the Pleistocene eruptions.  It may be that there isn’t enough data to exactly date when most species became extinct.

A decade after a supereruption, plants began recolonizing the ash-enriched soil from seeds and roots that survived inside the ashfall zone, and from plants outside the zone.  Animals from north, east, and south recolonized the west and within centuries, the region was probably as rich an environment in wildlife as it was before the supereruptions, minus the locally confined species that were lost.

The Yellowstone supereruptions impacted the rest of North America and even the world, though not to the catastrophic degree that devastated the west.  Weather systems brought up to an inch of ashfall as far east as Georgia and Florida.  This may have caused an increase in mortality among the wildlife here.  The ash from the supereruption blocked sunlight, resulting in a volcanic winter when for several years freezing temperatures occurred during summer, and winter temperatures plummeted far below average.  This phenomenon happened as recently as 1816 following the eruption of Mount Tamboro in Indonesia, a volcanic eruption that was much smaller than a supereruption.  1816 was known as the “year without a summer” and “eighteen hundred and froze to death.”  In New England there was snow in June and a frost in August.  The corn crop completely failed as far south as New York.  (The last supervolcano to erupt on earth was located in Java.  This eruption occurred 70,000 years ago and lowered earth’s temperatures for 1,000 years.) Volcanic winters following the Pleistocene supereruptions led to reduced plant growth and forest mast, resulting in significant wildlife mortality.  But wildlife was resilient.  Ground sloths and armadilloes stayed in their burrows, carnivores scavenged the animals that starved to death, and herbivores ate bark to stave off starvation til frost free summers returned.  Pine and oak trees are especially resilient and could rapidly recolonized even the ashfall zones.  Conifers continued to photosynthesize in low light conditions, while oak saplings germinating from buried acorns thrived in the sunny locations created in dead, shade-free forests.  All of the plant and animal species with us today are ancestors of organisms that survived past catastrophes such as volcanic supereruptions.

When the Yellowstone supervolcano next erupts, the human death toll will be in the millions.  The death zone will resemble that of a nuclear warhead blast.  Those living within hundreds of miles will be obliterated by the blast and lava flow.  Those living within a 1000 miles will have to cope with lung-destroying levels of ash.  Volcanic winters will disrupt the food supply.  The U.S. government was incapable of helping survivors of the Katrina hurricane, a minor disaster compared to a volcanic supereruption, so no one should expect any help from the government.  The United States and much of the rest of the world will splinter into hundreds of warlord-like entities, fighting over dwindling supplies of food in wars that will last at least a decade.

Lots of people, including me, laugh at survivalists who stockpile food and guns.  They will be the ones laughing after a volcanic supereruption when they roam through neighborhoods killing people and taking their food.

Tags: Ashfall fossil beds, volcanic caldera, volcanic winter, Yellowstone supereruptions will destroy the United States, Yellowstone supervolcano