The Yellowstone Caldera in Wyoming is widely known as being a supervolcano.
In the previous episode, I discussed the movement of the hotspot which formed several other
calderas leading up to the region in northwest Wyoming.
This video will discuss the three most recent caldera forming eruptions from this hotspot
which are termed the Yellowstone calderas.
Before I go in depth about these eruptions, I need to first mention how a caldera forms.
Caldera forming eruptions are quite rare.
For one to occur, there first needs to be a very large magma chamber present beneath
a volcano.
Then, during a very large eruption, a significant amount of the volcano's magma chamber empties.
Once the magma chamber is partially empty, the weight of the above rock makes it collapse
and fill what used to be a full magma chamber.
In some cases, large areas lose several thousand feet or hundreds of meters in elevation due
to a collapse.
The calderas created by these events form have a wide distribution of size.
They can be several hundred meters across, several kilometers or miles across, or up
to 100 kilometers or 62 miles wide.
Calderas that are dozens of miles in width typically require a vast magma chamber with
thousands of cubic kilometers of material to partially empty.
The first of the three supereruptions to happen in yellowstone, occurred 2.1 million years
ago.
This eruption was unfathomably large.
It violently erupted 2200 cubic kilometers or 528 cubic miles of ash, lava, and rock
in a rather short timespan.
To understand how large this eruption was, I will provide a comparison.
The Lassen Peak eruption of 1914 to 1917 in California was quite large.
However, if every named mountain in the United States was to have an eruption of this size,
all 73000 of them, it would still be smaller than this supereruption.
Recently, us geologists have discovered that this eruption didn't occur all at once, but
rather over a period of several years to decades.
We know this as the the eruption produced three distinct layers.
Each layer was separated by short periods of erosion and geologic alteration, which
suggest an interval of time between the large eruptions.
Overall, this eruption most likely occurred over a period of 20 or so years in three distinct
pulses.
The effects of this eruption aren't fully known, but it would have been drastic.
Large pyroclastic flows traveled over a hundred kilometers from their source, depositing a
unique type of rock known as ignimbrite.
Additionally, the majority of the continental United States, along with portions of Mexico
and Canada would have been blanketed with ash.
This ash would be thickest near the eruption, and decrease in volume as you go further out.
Areas far away such as what is now Boston probably received a trace amount of ash, while
areas closer to the center received a thickness of up to 1300 ft or 400 meters.
This eruption created the island park caldera, which today has some overlap with the two
recent yellowstone calderas.
This massive caldera is about 60 by 40 miles wide.
The second large yellowstone eruption occurred 1.3 million years ago.
This eruption dwarfed any eruption in human history in terms of size.
However, this large eruption was not considered to be a true supereruption.
Remember, to be considered a supereruption, a volcanic eruption needs to emit 1000 cubic
kilometers of tephra.
This eruption only emitted 280 cubic kilometers, and was about eight times smaller than the
previous supereruption.
This eruption created the Henry's fork caldera in Idaho, and deposited a discernible unit
of rock which is today referred to as the Mesa falls tuff.
The third and most recent of the caldera forming Yellowstone eruptions occurred 640,000 years
ago.
This eruption was larger than the Mesa falls eruption, but smaller than the Huckleberry
ridge eruption.
If you were to put all of the erupted products from this eruption into a cube, it would measure
10 kilometers or 6.2 miles on each side.
This eruption is called the Lava Creek eruption, and it created prominent tuff beds which can
be seen throughout areas of the yellowstone national park.
It deposited layers of welded tuff that were up to 660 feet or 200 meters thick.
After the eruption had ended, it formed a caldera which was more than 50 miles wide.
You might think that after these large scale eruptions, yellowstone would have been quiet.
However, this was not the case.
The next video will cover the volcanic activity which occurred after the formation of the
last caldera, and discuss the 4 volcanic eruptions it has produced in the last 10,000 years.
I hope that you enjoyed this video!
Part three will be posted tomorrow.
Once it is released, a link will appear on screen right here!