I have been doing this for two and a half years now…one-hundred-and-some-odd actual volcanoes and a few not-really-volcanoes…and all the time debating about whether or not I should pay a visit to one particular volcano. To be honest, I was worried that spending a virtual-vacation with her would give me the wrong sort of reputation. Oh I’ve heard plenty of talk around the internet about the sorts of things this volcano might do…bad things in the bad sense of the word….and there are certain groups of people who don’t even want to hear this volcano’s name because of such scandalous talk. So I came all the way to the northwest corner of Wyoming to get to know the Yellowstone Caldera for myself.
She’s not the sort of volcano people say she is….but whoa-howdy she used to be!Yellowstone Caldera’s origin is somewhat debated. The popular theory is that a hotspot (aptly called the Yellowstone Hotspot) has been slowly “moving eastward” and now resides beneath Yellowstone. Of course the hotspot is actually stationary and the North American tectonic plate is moving westward across it. This hotspot began making its mark across what would become the Snake River Plain, beginning around 16 million years ago at the McDermitt caldera near the Nevada-Oregon border, where a large lava dome collapsed and formed a caldera. That site now is best known for the valuable ores mined there in the 20th century, including mercury, uranium and cesium.
Then between 10 and 12 million years ago the hotspot moved on to the Bruneau-Jarbidge caldera in southwest Idaho, where a single event produced pyroclastic flows that burned and suffocated animals within 160 km as well as devastating ashfall that was carried 1,500 km down-wind. Shortly thereafter, geologically speaking, it moved on to the Twin Falls and Picabo volcanic fields 10 million years ago, producing the Arbon Valley Tuff.
Around 6.6 million years ago, the hotspot created the Heise volcanic field, and over the next 2 million years, produced four rhyolitic caldera-forming eruptions, ending 4.5 million years ago with the Kilgore Tuff, erupting 1,800 km3 of ash.
Finally, around 2.1 million years ago, the hotspot reached what would become the Yellowstone Plateau and proclaimed its arrival by erupting 2,500 km³ of tephra, spreading ash across more than half of the U.S., and leaving behind the Island Park caldera, measuring approximately 80 km X 65 km. This event laid down the Huckleberry Ridge Tuff, and is thought to be the largest eruption produced by the Yellowstone hotspot.
But it was not finished. 1.3 million years ago, at the western end of the Island Park Caldera, a new eruption disgorged 280 km3 of tephra and left behind the Henry’s Fork Caldera, whose western rim corresponds with the westerm rim of the larger Island Park Caldera. Measuring 29 km X 37 km, the Henry’s Fork Caldera may not be the largest, nor the youngest, but of the Yellowstone calderas, it is the most well-defined and visible. This eruption produced the Mesa Falls Tuff.
The final “super-eruption” occurred 630,000 years ago, creating the 55 X 72 km Yellowstone Caldera and emplacing the Lava Creek Tuff, 1,000 km3 of welded ignimbrite that measures up to 200 m thick in some places. A fourth caldera was formed at the West Thumb Geyser Basin around 174,000 years ago, but it pales in comparison to the others.
Yellowstone Caldera has also experienced effusive activity. Between 180,000 and 70,000 years ago, 600 km3 of rhyolitic lava flowed within the caldera, mostly from two north-to-south aligned chains of vents. Since then, the Yellowstone Caldera has managed to hold her magma, but is still quite active hydrothermally. The Indian Pond crater was created around 1350 BCE by a phreatic explosion.
But perhaps Yellowstone is known best for her dramatic waterworks. The area now included in Yellowstone National Park is known to contain 1,283 geysers, 465 of which are active in a typical year. There are 10,000 assorted geothermal features altogether…that being half of the world’s total geothermal features and two thirds of the world’s geysers. The most famous geyser is called Old Faithful with good reason. It erupts at relatively regular intervals ranging between 35 minutes and two hours. A typical eruption discharges 14,000-32,000 litres of boiling water as high as 56 m into the air with duration ranging between 1.5-5 minutes.
There are also hot springs in abundance thanks to the Yellowstone hotspot. Grand Prismatic Spring is the third largest hot spring in the world and in my own opinion the most fabulous. The colours are actually caused by mats of microbial organisms that live around the perimeter of the lake, and the hues actually change with season.
Yellowstone National Park now encompasses most of the Yellowstone caldera complex. The park was established by congress and signed into existence by President Ulysses S. Grant in 1872. Today the park covers 8,983 km2 and is home to wolves, grizzly bears, and herds of free-ranging elk and bison. The volcano is monitored by Yellowstone Volcano Observatory As for the popular notion that “she’s about to blow”…well…that’s a lack of understanding at best and a load of hooey at worst.
Oh…and did I neglect to mention we have a geyser-cam?
Congratulations to Glenn for finding me, as well as identifying Grand Prismatic Spring in my third clue. The first two features were Fern Lake crater and Duck Lake craters. Be here this coming Monday for a new challenge, and new adventure at a new volcano.