GSC 350 Project
#22 - The Yellowstone Caldera: Describe the possible effects of an eruption and how likely such an eruption is in the near future.

The Yellowstone Caldera

A caldera is a round collapse basin or depression. It is formed from magma being drawn up from an underground reservoir. This removal of magma causes the ground above to weaken therefore resulting in collapse. A caldera is similar, but different from a crater which is caused by the displacement of rocks during an eruption. Some calderas are as wide as 25 kilometers across and can explode more than 50 km3 of magma. A resurgent bulge forms in calderas as a result of magma being pulled to the surface. These can form small mountains which may or may not be eruptive. Mallard Lake dome of Yellowstone is an example of a resurgent dome.

The Yellowstone caldera is an old eruption site of a large volcano. It is a resurgent volcano, which tells us that since the time of its previous eruption it has been refilling in order to release its pressures, erupt, again. It creates a beautiful valley in the Wyoming area in the United States. It is covered with breathtaking geysers that are a result of its eruption and the heat underneath. It is the site of one of the world’s largest hydrothermal systems including the earth’s largest concetration of geysers.

Background of previous eruptions:
The Yellowstone plateau is had been developed through three different eruptions over a span of two million years. Some of the world largest eruptions are included within the Yellowstone eruptions. There was an eruption at Huckleberry Ridge Tuff 2.1 million years ago which created the 75km long Island Park caldera. The second was the eruption at Mesa Falls Tuff 1.3 million years ago that formed the 16km wide Henry’s Fork caldera. This is located in the western edge of the first caldera. The latest eruption, 640,000 years ago at Lava Creek Tuff formed the present caldera with a size of 45 x 85km caldera.

When did it occur?
The caldera has erupted three times in the last 2.1 million years. Scientists can only look at residue from volcanic ash, pumice and gas left behind rather than a human documentation due to the fact that it has not erupted in human history. It’s last eruption was 700,000 years ago.
What type of event was it?
Volcano: A Resurgent Caldera
A caldera is one of the largest volcanic structures. It embodies a huge volume of magma under its crust surface. The surface itself can be tens of miles across, making it not as noticeable to the human eye. The eruption was so massive, that it inside the caldera it is not noticeable that ones in a caldera because it looks the same as far as the eye can see all the way around them. Also helping this fact is that it erupts in a ring fracture; multiple eruption points forming a circle. See Figure 1. When the magma is released the top of the volcano, the crust, collapses on itself causing a broad depression where as opposed to a crater where the whole top is ejected. Once the crust collapses and is no longer there it resurges; the magma begins to push crust back up and rebuild. The Yellowstone caldera is being closely watched for resurgence, there are tilt meters and remote sensing. It is difficult to predict when a Caldera will erupt in the short term. Even so, there are possible precursors or warnings such as small earthquakes known as harmonic tremors.
The caldera’s eruption produced many geysers throughout Yellowstone National Park; the most known being Old Faithful. See Figure 2. The Yellowstone caldera produced over half of the world’s geysers.

Where did it occur?
In the last eruption 700,000 years ago the eruption caused the 35-mile-wide and 50-mile-long Yellowstone Caldera. The actual caldera is mostly in Wyoming, but the park reaches into the states of Idaho and Montana. See Figure 2. It covered such an area that the ash can still be found in places as far away as Iowa, Louisiana, and California. The ash reached as far West as California, as far South as Texas, East as Louisiana, and reached North into Canada.

What are its consequences?
The latest eruption of the Yellowstone caldera had a much smaller effect 700,000 years ago than it would have if it erupted now. The eerie truth is that the size of the magma chamber completely covers the old eruption area and even reaches farther than the old caldera, by quite a bit, in certain areas. See Figure 3. The ash flow would be so large that it would suffocate many people in the covered area. The pumice would get into the lungs. The population in the surrounding area would be greatly effected. The lava flow would destroy all in its way, including houses and structures as well as the beautiful features of Yellowstone National Park. The simple fact that the volcano is referred to often as a Super Volcano helps to bring the feeling of destruction. It would be a catastrophic event that would be a huge los of human lives as well as an undeterminable monetary loss. Mount St. Helens monetary loss was incredible and the Yellowstone volcano is expected to erupted with 10,000 times the force of Mount St. Helens. It is expected to erupt again due to the current activity of the geysers, steam vents prevalent in the park. See Figure 4. It would be absolute devastation for the Western United States.

How likely such an eruption is in the near future?
The USGS reports that following the paths that led to previous eruption at the Yellowstone caldera that there is a 93% probability that the caldera will erupt again within the next 150,000 years. Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which averages more or less 0.6 inches every year, as an indication of changes in magma chamber pressure. The upward movement of the Yellowstone caldera floor – almost 3 inches per year for the past few years – is more than three times greater than ever observed since such measurements began in 1923. From mid-Summer 2004 through mid-Summer 2008, the land surface within the caldera has moved upwards, as much as 8 inches in some locations. The U.S. Geological Survey, University of Utah and National Park Service scientists with the Yellowstone Volcano Observatory "see no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future. Recurrence intervals of these events are neither regular nor predictable. . ." It is suggested that no one in this lifetime will live to see it, but that even today it would be incredibly devastating and we cannot imagine the advances we would loose if it erupted say 100,000 years from now. The caldera has been resurging, in certain areas the ground is uplifting while others fall. This is a sign of an active magma chamber and due to this fact and the frequent swarms and earthquakes scientist know that it is in progress toward an eruption.

The Yellowstone Caldera may not erupt in our lifetime, but it will be a spectacular event and could quite possibly be one of the world’s largest eruptions. This would be the fourth cycle and due to the size of the magma chamber, quite possibly it’s largest. It is in the process of resurging and is still a great interest to scientists. Especially those at the USGS who are consistently monitoring is horizontal ground motion. See Figure 5.



Fig 1: Description of the ring fracture eruption of a caldera.

Figure 2: The size of the ash flows of the Yeloowstone Caldera
in two of its three eruptions.

Figure 3: The comparison of the size of the latest caldera and where the
placement of the current magam chamber is located.

Figure 4: Visual of the steam vents in the Norris Basin of
Yellowstone Nation Park's caldera.

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Figure 5: Horizontal ground motion 1997-2005.