The Yellowstone Volcano: Past, Present and Future
So please welcome Jake Lowenstern to talk about Yellowstone. For the next hour or so, we’re going to talk about Yellowstone. Yellowstone, for those who haven’t been there, it’s in the northwest corner of Wyoming. About 1000 miles to the northeast of us here. And it’s a pretty big park. It’s about 9000 square kilometers, or something like 3600 square miles. And for this Bay Area audience it might be useful to look at Yellowstone relative to the Bay Area itself. So that’s Yellowstone National Park. The pink line in the middle is the caldera. We’ll talk more about that, but the outline of the park is here. So it stretches pretty much from San Jose to San Pablo Bay and from Bolinas all the way over to Pittsburg. It’s a big park, and so when we talk about things happening at Yellowstone, you have to think a little bit big.
Yellowstone is many things to many people. It of course is the first National Park in the United States and it was the first National Park in the world and it started a trend of humans trying to preserve their wild places for the benefit of future generations, and so Yellowstone is a really special place just from that standpoint alone. Of course it was preserved primarily because of the amazing geothermal features that are there. The geysers…. pressurized boiling waters…. a boiling groundwater system. Its spectacular Rocky Mountain scenery. Its world-class fly fishing. Its charismatic megafauna, as they are known. Lots of animals that have a place to breed because we have such a special large, wild wilderness area for them to hang out in, where they’re free from hunters and other problems we often have with our civilized society. Of course, more and more lately Yellowstone is starting to be known as the supervolcano.
And along with that we get a lot of crazy publicity, with articles in newspapers often highly exaggerated and very frequently with a great deal of misinformation. So we’re going to try and cut through some of that today and see what really has happened at Yellowstone. What’s possible at Yellowstone. And we’re going to do that starting out with what we know about Yellowstone, and go through a short history of the park and our understanding of the geology and volcanology of it. We’ll then talk about the primary geologic hazards and their relative probability.
What’s more likely than other things? What’s actually happening right now? How do we go about monitoring Yellowstone? What are the techniques that we use and what do we learn? And then a little more about the prospects for future activity. And any of those who want to stick around we can do plenty of questions and answers if you’re still awake. Originally there wasn’t a whole lot known about Yellowstone except the legends of the Native Americans and the tall tales told by the trappers. Jim Bridger here talked of petrified forest with petrified birds singing petrified songs. And he talked about rivers that raced downhill so fast they turned warn on the bottom.
But there wasn’t a lot of cold hard facts. Congress finally put together a whole series of expeditions to explore the various parallels and Ferdinand Hayden was one of the people who ran the expedition that went through Yellowstone in 1871. These were the groups that eventually got the U.S. Geological Survey started about ten years later. Hayden brought along William Henry Jackson, a photographer, and Thomas Moran, a painter, to help document what they found in the area. They collected samples, they documented what they were seeing, and they did it both through the photography and the painting. Those materials went back to Washington and they were really instrumental in having Congress set aside Yellowstone as a national park.
Hayden also figured out quite a lot about the geology. He recognized that this was a volcanic area. And so here as he was looking out from Mount Washburn over the surrounding terrain he said : “..it is probable that during the Pliocene period the entire country drained by the sources of the Yellowstone and the Columbia was the scene of as great volcanic activity as that of any portion of the globe. It might be called one vast crater, made up of thousands of smaller volcanic vents and fissures out of which the fluid interior of the earth, fragments of rock, and volcanic dust were poured in unlimited quantities ….
Indeed, the hot springs and geysers of this region, at the present time, are nothing more than the closing stages of that wonderful period of volcanic action that began in Tertiary times.” So he recognized that this was a volcanic area. He recognized that it was not TOO long ago in the geologic past that it was active. He put it a little bit older than it actually is, and he also recognized that the hot springs and hot water are in some way related to the volcanic system.
He and his colleagues camped on the north side of Yellowstone Lake and they experienced another remarkable thing that we know about Yellowstone that there are a lot of earthquakes. They experienced what we now call an earthquake swarm, where they were awakened in the middle of the night by a series of shocks that woke them up, woke their horse up, and were shaking the trees. And this is a little quote from Albert Peale, one of the people on the expedition. Philetus Norris was the second superintendent at Yellowstone and he had the good fortune of witnessing a hydrothermal explosion… sort of a “geyser gone bad,” where rocks are thrown out into the air. And he has a great quote here: “The pool was considerably enlarged, its immediate borders swept entirely clear of all movable rock, enough of which had been hurled or forced back to form a ridge from knee to breast high at a distance of from 20 to 50 feet from the ragged edge of the yawning chasm.” So a very alliterative quote.
This photo here is the hydrothermal explosion… something that we’ll talk later on tonight. And then Thomas Jaggar who later founded the Hawaiian Volcano Observatory, went to a place called Death Gulch, and saw seven grizzly bears that had imbibed a bit of poisonous gas and he wrote: “… the poor creatures are tempted one after another into a bath of invisible poisonous vapor, where they sink down to add their bones to the fossil records of an interminable list of similar tragedies, dating back to a period long preceding the records of human history.” These guys knew how to write back then. And they also made a lot of great observations. So we knew that there was a lot of gas coming out at Yellowstone.
There’s earthquakes there, there’s hot springs. It’s a big volcanic system. And so the stage was set… It wasn’t really though, until the 1960s when a modern perspective on Yellowstone came to pass. This is Bob Christiansen (Chris). He works here. He’s retired now, but works out of the USGS in Menlo Park. And he spent much of his career working at Yellowstone. And over here on the right is a picture of a thin section of the Lava Creek Tuff. Tuff is a word for a kind of rock that had been known to be present all around the Western US. In the 1950s, a guy named RL Smith, out of the USGS in Reston started doing a lot of work on this particular type of rock.
They’re fragmental rocks, and they contain crystals and they contain a lot of glass. And so in this example from Yellowstone, there’s a little glass shard. The glass is quenched silicate melt. It’s the melt that’s present in a volcanic eruption. Bubbles form as gas comes out of solution when the eruption is starting. The material is going into the air and the liquid quenches into glass. The bubbles break and form little glass shards that are swept along in very violent, very hot clouds that fill in valleys and are called “tuff,” or called ignimbrite, also called pyroclastic flow.
In this case, there’s such a thick amount of material that gets deposited and it’s so hot, that it starts to weld over time. It condenses. And all the little glass shards tend to get stretched out and aligned. So the glass shards stretch out and you can see they wrap around this crystal that is a much tougher, less pliable material. Anyway, these kinds of rock, the welded tuffs, are evidence of massive volcanic eruptions. And Chris was able to find not just one of these eruptions, which they knew about, but he found that there were three separate eruptions that had happened relatively recently in the geologic past. There was the Lava Creek Tuff that he mapped out in green here. This is a map of how it would have looked 640,000 years ago, right after the eruption of the Lava Creek Tuff.
And preceding it was the Mesa Falls Tuff, and before that was another, very, very large eruption, the Huckleberry Ridge Tuff (purple). So the material comes out and moves down valleys and sometimes is many hundreds of feet thick. And it completely fills in this area here, which is called the caldera. Now, in the case of the Lava Creek Tuff, there’s a thousand cubic kilometers of material that got taken out of the ground, more or less, during that eruption. That’s enough material to bury the State of Texas about five feet deep. So it’s a really big amount and it all came out of Yellowstone. So when you take that amount of material out of the ground, and you put it on top of the ground, you’re left without a whole lot of support for the ground surface, and it caves in.
It’s what we call a caldera. It’s kind of like a giant sinkhole. These are all the fractures that are associated with the formation of this caldera. And all of this happened 640,000 years ago at Yellowstone. It’s the last really large eruption in this particular place. I’m going to really focus in this talk on what the USGS did at Yellowstone, also some other colleagues, but we’re here in Menlo Park and I want to focus on some of the work that’s been done in this particular location.
These guys right here had an amazing time back in the 60s. On the right is a guy named Don White and on the left is his protégé Bob Fournier, who’s around and still lives in Portola Valley. We see him pretty frequently. These guys were funded, as was Bob Christiansen by NASA to do studies at Yellowstone. And they got the opportunity to study the geothermal system and to drill 13 science exploration wells into the geyser basins at Yellowstone. First of all, that would be very difficult to get permission to do today, so we’re very grateful to them for what they were able to learn, and for the samples that they collected in drillcores. We’re able to use them today because they’re sitting in a warehouse in Denver. Anyway, these guys wrote a lot of very classic papers on Yellowstone and a lot of what we know about geothermal energy production really came from the work that was done back in the 60s. Here’s an example of one of the wells that they were drilling at the time. So the next really remarkable thing about Yellowstone is that it moves up and down.
The ground surface is unstable and over time it moves. Bob Smith, who’s down here, was one of the party that came in and re-surveyed a series of roads that hadn’t been surveyed since the 1920s. Dan Dzurisin also worked on this topic. He’s at the Cascades Volcano Observatory, and here he’s carrying this tripod that was used for leveling. Well Bob and his colleagues re-occupied the benchmarks that were done previously in Yellowstone, and this is a contour map that shows the number of millimeters that the area had gone up between the 1920s and the 1970s. You can make out 500, 400, 700 is the largest one in the middle. Here’s the caldera, and so most of the activity here is going on in the caldera, and the maximum uplift is about 700 mm in between these two areas that we call the resurgent domes, the areas of maximum uplift within the caldera. So 700 mm is 70 cm, it’s around 2 feet… and so that had happened in those 50 years. This was really a remarkable observation and something that we’ve been tracking ever since.
Bob Smith by the way, is one of our collaborators at the University of Utah through the Yellowstone Volcano Observatory, and he’s been working there on a very, very productive career for many years. The last topic I want to bring up is the gas flux from Yellowstone, which is something that we didn’t know about until about ten years ago, at least in terms of its magnitude. Here are my colleagues Bill Evans and Deb Bergfeld who are trying to figure out how much gas is coming out of this particular pool at Terrace Springs. Over here is Cindy Werner. She’s now at the Alaska Volcano Observatory, but she did her PhD at Yellowstone using this, an accumulation chamber. Here’s an example of some more modern ones. These look at the flux of gas through the soil. If you have enough of them and you spend enough time in the field, in her case, many, many summers, going to many places and running grids, she was able to ascertain that a very high flux of gas is coming out of Yellowstone, on the order of 45,000 tons of CO2 every single day.
And that makes Yellowstone one of Earth’s most prolific natural sources of carbon dioxide, comparable to a pretty big coal-fired power plant. It’s similar to Mount Etna and similar to what comes out of Kilauea in Hawaii. Basaltic magma, that’s the kind that gets formed deep down in the Earth’s mantle, contains a lot of carbon dioxide when it comes up towards the surface. So when you see a lot of carbon dioxide, that’s a typical thing for a volcano, but its something we didn’t necessarily know was happening at Yellowstone, and by seeing that big number we can equate Yellowstone with some of the other big volcanoes on Earth.
Let’s step back a little bit and try to understand how this works on a larger scale. This is a map of the Western United States. (Shows Idaho and Wyoming, followed by , Oregon, Utah and Nevada). This is a feature called the Snake River Plain. Idaho Falls and Twin Falls are there. The Snake River runs through it. It is very productive farming country. It’s also very flat. Underneath all that flat terrain is a whole series of old volcanic calderas very similar to Yellowstone. Around 16 to 17 million years ago there was a rifting in Northern Nevada. There was the outpouring of the Columbia River basalts in Oregon and Washington and there were calderas forming in northern Nevada, and these numbers, 16, 14, 12, 11, are a progression in the occurrence of these caldera systems that move towards the northeast and towards the present day Yellowstone. So there have been a whole series of Yellowstone-like features that have existed in the Snake River Plain over the last 16 million years.
The North American Plate is moving towards the southwest, and so it’s overriding an area within the earth’s mantle, down 50, 60, 70 kms. Kilometers by the way are 0.6 miles. I’m a scientist. I tend to use the weird metric units a lot, so please divide if I don’t translate into English (units). The plate is moving overtop this melting anomaly in the mantle. So we have a progression in these caldera systems that get younger and younger toward the northeast, ending up with Yellowstone today. This is what the Snake River Plain looks like. This is from the Craters of the Moon. It’s very flat and this is what Yellowstone will look like a few million years from now. Eventually, it’s going to cool down. The land is going to subside, and sink. We’re going to continue to have outpouring of mantle rocks but not as much melting of the upper crust as happens at Yellowstone today.
It will all get buried and flattened, and they’ll be growing potatoes on it. This is an example of seismic tomography of the Yellowstone plume or hotspot region. In this case on top we’re looking at the surface of the earth looking out from Yellowstone to California. Yellowstone. Snake River Plain, Basin and Range, Sierra Nevada and Central Valley. So this is now looking at a slice down into the earth. The is in kilometers , 200, so about 100 miles deep. And the colors represent the velocities of seismic waves that are moving through the crust . To make these diagrams you are looking at earthquakes that are happening across the globe. And you’re looking at which regions the rays from the earthquake are coming in quickly and which ones where they’re delayed. And they’re able to put together these maps and show that the mantle of the earth beneath the Snake River Plain is slower, the earthquake waves move slower through that region, and that’s either because it is hotter, or it’s partly melted.
And that’s not something that you see, for example, beneath the Central Valley. This is an area that is fairly unique. We have a lot of melting going on and that ultimately is what is producing basaltic magmas, similar to Hawaii, that are coming up to the surface beneath Yellowstone. Here’s another cross section, again where you’re looking at depth, where this is to the base of the crust beneath Yellowstone, 40km, something like 25 miles. You have the basaltic magma, that’s liquid. It’s molten rock. It’s coming off the mantle. It’s rising into the crust. The crust of the earth is less dense and it contains materials with higher amounts of silicon dioxide.
It melts fairly readily. You mix what melts in the crust with what’s coming from the mantle, and you eventually create magma reservoirs high up in the crust that are less dense than the materials coming in from below, and they’re also “thicker”, more viscous, and much more explosive. And that’s how you get these accumulations of fairly explosive magma up in the crust at depths 5 to 6 miles beneath Yellowstone. OK. So let’s talk about some of the hazards at Yellowstone. In this series of slides I’ve got this blue dot and it’s going to move over from low frequency events to high frequency events. Low frequency events might occur every 100,000 or every million years, and an example of those would be the big volcanic eruptions at Yellowstone, these caldera-forming eruptions. There have been three remarkable ones, and there is ash that can be found from these events as far away as Texas. So they’re putting ash high up into the atmosphere, into the stratosphere and it comes down a long ways away. So these are big events, but Yellowstone may be done with this particular type of event.
There’s no reason it ever has to happen again. Volcanoes do live and die eventually. And Yellowstone may have finished the amount of highly silicic melt that it can extract out of the crust. But it is also possible that we could see another one of those eruptions again at some time in the future. In general, they are very, very rare events… not only at Yellowstone, but also around the world. Just to give you an idea of what might happen if this ever did happen again, one of my colleagues at the Cascades Volcano Observatory, Larry Mastin, has done some simple modeling, using wind patterns that we have available to us and tossing ash and replicating the Lava Creek Tuff eruption. In this case, he took wind data from 2006, for a specific week, April 21-27, he put 300 cubic km of material into the air and let it settle out with the wind patterns that were present, and you can get an idea of what would happen. There are some fingers coming out above the Great Lakes. But this color is 1-3 mm. So even though you hear about how these are enormous events, most of the material is falling out either within the caldera or in areas immediately east of Yellowstone.
Now you can choose another week and you get a fairly different result. Every possible week that you can have an eruption, you will get a different event. You can’t just say: “This will happen,” because it depends on how the volcano erupts, the amount of time it takes and the specific wind conditions. In this particular case you get some fingers of 1–3 mm of ash that make it near the Great Lakes, and almost over into New York State. But for the most part, the eastern United States doesn’t end up getting a lot of ash even from a giant eruption. These eruptions in the past have a remarkable effect on the landscape. Here are the Rocky Mountains. Yellowstone Lake sits right here.
Here’s the Yellowstone Caldera. There’s the Grand Teton Mountains. You’ll see the Tetons march up here. There’s all sorts of ranges, the Gallatins, the Absarokas, but there’s no big mountain ranges within Yellowstone (caldera) itself. And that’s because during these big caldera-forming eruptions — especially the first one and the third one — the mountains eventually fall into the caldera, and they disappear. And then later on, new lavas come out of the ground and bury the previous landscape. These are big events and they have big impacts. The reason that Yellowstone looks like it does is because of its geological history. OK. This slide shows you the park boundary. It’s about 100 km or 60 mi on a side. Here’s the caldera, which we’ve seen several times now.
Here in pink are the roads that run through the park. I’m now going to show you everything that’s happened at Yellowstone in the caldera since the last caldera-forming eruption (640,000 years ago). All of these are lava flows, in some cases very big lava flows, and they buried the topography and flattened out the pre-existing topography. This is one of the larger ones. It’s called the Pitchstone Plateau. It’s about the size of Washington, DC. It’s anywhere from about 50 to 300–400 feet in thickness and sometimes a little bit more, and it’s 70,000 years old. So this is the last volcanic eruption at Yellowstone. Since that time, there has been no volcanism at Yellowstone. But all of these lava flows came out since the last big explosive eruption.
A lot of times you’ll hear, if Yellowstone erupts… THIS (and they’ll talk about the worst-case scenario). But this is what’s been going on for the last 30 or 40 big eruptions at Yellowstone. If you’ve been to the Grand Canyon of the Yellowstone, you were looking at one of these post-caldera lava flows. If something like this came out today, it would be a big deal in Yellowstone National Park.
But it wouldn’t have a lot of explosive activity, it wouldn’t be a national-scale emergency. It would be very much a local event. But it would still be very spectacular. Another thing that’s happened since the last caldera-forming eruption is all of these yellow lava flows, and these are all basaltic lava flows. These are the sorts of materials that are created in the Earth’s mantle.
Normally if they come up beneath the caldera we have all of this silicic magma, the stuff that forms the explosive eruptions. It’s high up in the crust and it doesn’t allow the deep magma to come up and penetrate through. They pond below, just like in the figure I showed you a little while ago. Outside the caldera, the crust is cool. The rock can break and the basalt can come out and form nice little flows, like you see at the Sheepeater Cliffs, and this is an example of what one looks like in Hawaii. You can imagine what it would be like if it happened at Yellowstone. So these events occur more on the order of every ten thousand years. They actually appear in groupings The last one was 70,000 years ago, so they don’t always occur every ten thousand years. There’ve been about 80 eruptions since the last caldera-forming eruption 640,000 years ago, and the last one was 70,000 years ago.
Even more frequent are hydrothermal explosions. This is where the hot-water system that underlies Yellowstone becomes unstable, and the water flashes to steam, throws rocks out onto the surface and can create fairly large holes in the ground. This is called Indian Pond. It’s about 1000 feet across. It formed 4000 years ago. There were a lot of these events within the past 15,000 years at Yellowstone. The largest of them forms Mary Bay within Yellowstone Lake. It’s two miles across. So if you think about the way that geothermal systems are established…
If you drill into a geothermal system, the boiling temperature of water at the surface is 100°C. At Yellowstone, you’re at a higher elevation and it’s 92°C, or about 200°F. But as you go down in the ground, the pressures increase. The boiling temperature increases, just as it would in a pressure cooker. And so the temperatures once you get a few hundred feet down, are much, much higher than they would be at the surface. So if you’re able to depressurize that system, you’ll take water that’s way above it’s boiling point at the new lower pressure, and it’ll catastrophically explode into steam, breaking rocks along the way, and forming these very interesting landforms. Here’s an example of what one looks like at Biscuit Basin. And this is one that a whole field trip of geologists was witnessing. The park geologist Hank Heasler and Bob Smith from Utah were there to witness this at the time.
This is not a big one, but it gives you an idea of what one might be like. And here is a map of where these hydrothermal explosions are located at Yellowstone. All postglacial, so all in the last 15,000 years. A lot of them near the north end of Yellowstone Lake, forming holes in the ground that are fairly large. And so this is a hazard that definitely is present at Yellowstone today, on a more frequent basis than something like a volcanic eruption. Here’s another series of slides. These are faults… areas that have broken rock. These are associated with the resurgent domes where the caldera moves up and down.
These are associated with tectonic movements associated with the Tetons. And there’s also other earthquake faults out in this direction near Hebgen Lake. Here’s where a lot of the earthquakes have occurred at Yellowstone over the past 25 years. Just a representative sampling. You’ll see there’s a lot of earthquakes out hear near Hebgen Lake. And that’s probably because it’s near the location of the M7.5 earthquake that occurred in 1959, I’ll take about in a moment. But there’s earthquakes all around the caldera as well. Most of the earthquakes are small. They’re magnitudes 1s and 2s. Occasionally 3s. Most of them are not felt. Occasionally there is a big earthquake. And there might be a big earthquake somewhere in the Yellowstone area every 100 to 300 or 400 years.
The last really big one was this M7.5 in 1959. It occurred outside the park at Hebgen Lake. It caused a big landslide that buried a campground and killed around 20 people. And here is a slide from Bob Smith showing the offset, the actual scarp that was formed from breakage of this fault was 3 geology students tall… so it’s a pretty sizeable earthquake. So this is a geologic hazard that’s again much more present in the area than volcanic eruptions. Something that the people living in the area need to be familiar with. And here’s some photos from the 1959 earthquake. OK. Monitoring Yellowstone. Well, you’ve now gotten the picture by now that Yellowstone does have a lot going on. It’s an active place. We have a volcano observatory there partly because we feel we need to keep an eye on it, because it does have this big hazard that’s a possibility there, but also because it’s a globally unique place. There is no place on Earth that’s quite like Yellowstone. It has this big magma system. There’s contantly things happening. And so we feel it’s important that we as scientists know what’s going on there and can present that data and can publish it for our colleagues all around the world.
Because what we learn at Yellowstone really teaches a lot about volcanoes everywhere. A lot of volcanoes don’t do anything. They sit there having no activity at all until about two weeks before they erupt. At Yellowstone we’re constantly seeing activity even though it hasn’t erupted for 70,000 years. So it’s an interesting place to do work. We have a volcano observatory that’s set up to look at Yellowstone, and it has eight member institutions. The USGS, who runs the other volcano observatories, but also Yellowstone National Park, the University of Utah runs the seismic network at Yellowstone and has for over 40 years, and they’re very active, they receive a co-op through the USGS to work there, there’s also the University of (indended to say Wyoming), the three geological surveys of Montana, Wyoming and Idaho, and UNAVCO, which is an organization that runs through a contract from the National Science Foundation to run a lot of geophysical equipment, some of which we have at Yellowstone.
So we all work together. It’s a virtual observatory. There’s no buildings that we have at the park. We go to Yellowstone. We collect data. We have data that’s streaming over the internet, that we all get a chance to look at, and you can all look at it too, because it’s all available for the public. Here’s an example of our seismic network. There’s around 30 seismometers spread around the park. When you have a seismic network you’re able to locate earthquakes. You’re able to find out where they’re happening, how deep they’re happening and how large the earthquakes are. This is an example of the earthquakes that occurred at Yellowstone last year. There were about 1900 earthquakes. In this case they’re sized by the magnitude. So you can see that most of these earthquakes are much too small to be felt.
There were maybe 4 or 5 last year that were big enough to be felt. They’re color coded by time. And so you can see that different groupings of earthquakes occurred at different times. The blue ones are the earlier ones, such as these by West Thumb. The yellow ones occurred later in the year. Some of these red ones occurred in December. These are all little earthquake swarms.
And it turns out that about half of the earthquakes at Yellowstone are in these swarms. They’re little groupings of earthquakes. An area might become over-pressurized and the earthquake swarm relieves that pressure, in that particular area. And it’s very common. We might get a week that goes by where we’ll see 50 or 60 earthquakes in one particular area and then we won’t see any more earthquakes for the week after that. Another thing we have is GPS monitoring. These are fancy GPS receivers attached to monuments. We have well over 20 GPS receivers around the park and maintained by UNAVCO. The next data I’m going to show you is from the White Lake area in the eastern part of the caldera.
Here you can see one data point for each day. We actually get data out of these things every second. We typically average a day’s worth of data, and here you’re looking at time from 2005 to 2014. You can see that this particular station was moving west; it was moving south; and so southwest is the direction that all of North America is moving. It’s moving along with the rest of the continent toward the southwest. But it’s also moving up and down. From 2005 to 2009 or 2010 it was moving up, and in this particular case moved up about 20 cm (8 inches). And then it started going down in this time period here. So the great thing about these GPS receivers is they allow you to look in great detail at one spot. And we have 20 or 30 spots, so we can look at each in great detail and get a feel for day-to-day variations. If something starts happening, you go to the GPS and see if the ground surface is moving up. We have another technique that’s called InSAR. It’s another satellite-based technique like GPS, and one of the people who works on it is Chuck Wicks, who’s a scientist in Menlo Park.
And he produced this particular image, and it’s called an interferogram. Now InSAR is a radar technique. You have a radar up in space and it’s taking an image of the land surface below. It’s scanning the land surface. You take an image and compare, in this case it’s maybe 1995 to 1997, two years apart, and you’re looking at how the ground surface changed in elevation relative to that satellite. And what you get here is like a contour map. Any yellow ring, for example, is going to represent places that moved up a similar amount towards the satellite during that time period. Same goes for this yellow ring or this pink ring. And when the rings are really close together, that means that there was a lot of movement in that particular area.
During 1996-2003, there was about 12 cm of uplift over that time period, something like this amount (shows with hands), over an area about 5 miles across. It’s a large volume increase, though it dies off when you get to his area out here in the middle of the caldera. So instead of looking a various spots (with GPS), where you might sort of get a feel for what’s happening, a map like this really gives you an understanding on a map view of where the ground is deforming, where it’s moving up. Another satellite technique that we use looks at heat flow. This is Greg Vaughan who works at the USGS in Flagstaff. He uses the ASTER satellite, and he can specially send it to look at Yellowstone at night when the sun’s rays are no longer heating the ground. And can look at those areas that are hot, and those areas that are not as hot.
So some of these areas only have a little anomaly and some have a lot of watts per square meter. A lot of energy is coming out of the ground, such as the Sulfur Hills here, or some areas within the Norris Geyser Basin. And so this is another technique that we can do, every ten years or so, to compare if things are changing within the park, and we can also use some other satellite-based techniques as well. Couple other techniques we have. We look at river discharge and temperature. We look at some geyser behavior. We look at geophysical things like tilt and strain. Right here I have a couple images that look at temperature and water flow. In this case, it’s related to the eruption of Steamboat Geyser, it’s Yellowstone’s tallest geyser, sending water over 300 feet into the air.
This is close to it in an image from 2005. Last summer Steamboat erupted again. This is from a temperature gage that we have in the outlet, right below the geyser. And here is time on the bottom (x-axis), and right there is when there was a big spike in temperature, a couple hundred feet away from the geyser itself. And you can also find that about a mile away, and an hour later, there was a big pulse of water that went out through a stream gage on Tantalus Creek. So this is discharge here versus time. This peak lines up with this peak. And another neat thing that you can see with this particular diagram is that before the eruption there were all these tiny little peaks, which represent small eruptions of Steamboat sending water maybe 15 or 20 feet in the air. As soon as the big eruption occurred where the water came out for an hour, hundreds of feet in the air, nothing came out of the geyser anymore. So all you see here is a nice flat curve that represents the daily variations in temperature that you would normally measure in any creek.
So those are the kinds of things you can learn from data that we have streaming on the internet and that you can look at every day. In the next series of slides I’m going to talk a little bit about what’s been happening in the last ten years at Yellowstone… some of the more exciting things that we’ve been noticing. First one I’m going to talk about is the Denali Earthquake. Then we’ll talk a little more about uplift in the caldera. Some of the hydrothermal disturbances at Norris Geyser Basin. And some swarms that occurred in the last few years. This part is a little bit more technical, but try to stay with me. The Denali earthquake occurred in 2002. And it was a magnitude 7.9 that occurred on the Denali Fault up in Alaska. Any time you have an earthquake, especially on a strike-slip fault, you’ll get surface waves produced. Those are the ones that do a lot of damage to buildings.
And in the case of this particular earthquake it sent big surface waves out in a southeasterly direction. Now every one of these little diamonds here represents a seismic station. And the ones that are red are “pegged out”. They’re clipped data because the surface waves that were coming from that earthquake were so big, even down in Montana and Wyoming that the seismometers couldn’t record the data. There was too much shaking and so it’s what we call “clipped.” Whereas the blue stations there was a little bit less ground surface wave movement down into California for example. These are figures from a paper by the University of Utah group. Stefan Husen was the main author. And this one over on the right, you don’t need to worry about to0 much, but it’s calculating the stress level associated with these surface waves.
Well when the ground shaking got to Yellowstone, it set off earthquakes all over the place. They were small earthquakes, magnitudes ones, twos and threes, but some of them were felt. And this is a remarkable example of something that wasn’t even known about until the early 90s. That is, the phenomenon of triggered earthquakes. That you could have an earthquake at one location and that the waves that are moving around the earth are actually triggering earthquakes at (a distant) location, although much, much smaller earthquakes. And so you can see here, that most of the events were within the first couple hours of the Denali earthquake surface waves hitting Yellowstone. So it also illustrates just how pressurized and ready for earthquakes Yellowstone is, and how easy it is to set off Yellowstone, at least in terms of producing earthquakes. Another thing that happened back around that time was that there was a lot of hydrothermal activity in the Norris Geyser Basin area. There was a new linear vent that formed at Nymph Lake.
It formed some really loud jet-like thermal features. A lot of trees died in the area. The Park Geologist Hank Heasler spent quite a bit of time documenting the changes. Later that summer there was a whole region in the Norris Geyser Basin, the Back Basin, where there was anomalous activity in a lot of the geysers, ground temperatures that were increasing and pools that were turning into steam vents or fumaroles. Here’s an example of a thermal image taken on the trail. And you can see that some of the temperatures right on the trail were hitting above 50°C. There were measurements right off the trail that were the boiling temperature of water. So if you were walking barefoot, you would have been pretty uncomfortable.
But the Park Service closed off the Back Basin for a period of about a month, and things cooled off and went back to normal. A final thing that happened in this time period was Steamboat Geyser. It went off six different times in the period between 2000 and 2005, with most of them happening in 2002 and 2003. Then it went to bed after 2005. It didn’t erupt again until this last year. And our colleague Chuck Wicks—I showed that interferogram with the northern part of the caldera that was experiencing uplift— he hypothesized that maybe the uplift in that area, there were maybe some magma there at great depth and it was pushing up on the crust, and that causes maybe a little bit of tension at the surface, and maybe that was enough to let more of the deep thermal fluids to get out and cause some of the ground heating and some of these other strange behaviors.
And he may well be right, we don’t know for sure, but what we do know is that when deformation in that particular area stopped, we stopped seeing a lot of the strange hydrothermal activity. So we probably want to see a few more cycles of this before anyone will believe it, but … interesting observation. This is another one of these interferograms produced by Chuck Wicks. And it shows you what happened after this area up here stopped rising. The main caldera started to go up. Again we have this bullseye. Maximum uplift is in the center. It falls off as you move to the edge. And the area near the Norris Geyser Basin and the northern caldera is going down from 2004 to 2009. So this part goes up, and the part that had been going up before, now goes down.
And this is really an immense amount of uplift, especially when you consider how big the area is, something like thirty miles across. All of that area going up as much as 25 cm or even 20 cm… it’s a big volume change, and probably because there’s some magma coming into the system at depth and is pushing the ground up a little bit. The uplift went on until around 2009 but eventually it stopped, and one of the interesting things, which has been noticed several times now, is that the uplift often stops when there are big earthquake swarms. The earthquake swarms appear to be relieving the pressure on the system. You have uplift… things are gradually moving up. You have the earthquakes and things start to settle again. These are seismograms. The one on the left is from a station at the north end of Yellowstone Lake and the one on the right is at the south end of the lake. All of the data are for the 27th of December 2008. These are from the Yellowstone Seismic Network. You have time starting from early (at the top) to late (at the bottom). Each 15 minute period is one line. Four lines would be an hour.
These are all earthquakes. When you’re on a black line the earthquakes are all black. When you are on a red line the earthquakes are all red. Every time you get a squiggle, you are looking at an earthquake. In this particular day…. you have a lot of earthquakes. And the biggest one was a magnitude 4. There was also one M3.5, M2.0, there were a number of felt earthquakes. This happened in December, there weren’t a whole lot of people around. Yellowstone was pretty cleared out. There were maybe 15 or 20 people who were living at Lake at the time, and they were feeling many of these earthquakes. It happened for about two weeks. The data were later reduced by Jamie Farrell.
He was a PhD student, now finished, at the University of Utah. And here are a couple maps that show you what was happening during that period of time. It turns out that the earthquakes were on a linear trend. The left is a map view. The blue are the early earthquake and the red are the latest earthquakes. They started at the south and they slowly moved north. This is another one of these cross sections. Now you’re looking down into the crust, ten kilometers deep. South to the left, north to the right. The biggest earthquake is down at depth. And as time went on the earthquakes moved more toward the north and there were fewer and fewer deep earthquakes. This was a pretty nervous time for us, not only because there were a lot of earthquakes, but also because people get rather agitated when things are happening beneath lakes. Lakes freak people out. You can’t see what’s going on. You can’t see that nothing is happening. And so people hypothesized all sorts of crazy stuff.
And it was a nervous time. There were a lot of earthquakes going on, but there were never any steam explosions, never anything happening other than these small earthquakes. Then there was another earthquake swarm and this one was the next year, 2010. In this case, instead of over hear by the lake, we had an earthquake swarm over here on the western side of the caldera, and this was about two and a half times more earthquakes; about 2500 earthquakes over a two month period. Most of the earthquakes were within the first few weeks. People didn’t seem to get as nervous about this one. Mostly because it wasn’t under a lake. And it was under an area that was just a big lava flow. There wasn’t anything terribly interesting out there on the Madison Plateau. But it still turned out to be a really interesting series of earthquakes. David Shelly who works here in Menlo Park just published a paper where he used some interesting techniques called waveform-based detection and relocation. Normally if you’re measuring earthquakes, you have a big cloud of earthquakes and you can’t really make out how they’re all related to each other because they’re using data from seismometers that are distant from each other.
If you really focus on just a couple good sets of data, and you use relative locations, you might not get an accurate location for any particular earthquake, but you can look at their relative locations. So that’s what he did. I’m going to show you a movie that represents the earthquakes and there are 8700 events that he’s able to detect… way more than you can get with the seismic network itself. You can see that all those earthquakes are aligned on a single fault that’s dipping to the east. So they’re on a plane. The colors represent different times. The blue ones are early… the 18th of January and the red ones are happening later. You can see there are little “squirts” of earthquakes that are happening along this plane.
The thought is that there are fluids that are released on one part of the fault and they lubricate other areas and allow additional earthquakes to nucleate, or occur. So that’s a neat example of how some of these things work. Now it’s time for questions. I made questions first, ’cause I have questions that I get asked all the time, and I figured I’ll just cut to the chase and I’ll ask some questions. You can answer questions later on. When will Yellowstone erupt again? Somebody was going to ask that, right? And the answer of course is “we don’t really know.” It hasn’t erupted for 70,000 years, and even when we had these immense hydrothermal explosions back in post-glacial times 5000 years ago, there was never any evidence that any magma was involved.
It could erupt. It could erupt next year, but probably not. I don’t expect it to erupt within my lifetime. But at some point in time it will erupt. It just might be a thousand or ten thousand years from now. What will the eruption be like? There’s an outside possibility that it’ll be one of these supereruptions, but that’s by no means the most likely scenario. And as I said before, it’s perfectly possible that there never will be another supereruption out of Yellowstone. We’ll get one somewhere on Earth, but Yellowstone’s already had three pretty big eruptions, and most of these volcanoes don’t have four or five.
They use up all of the crust that’s available to melt, and they lose their ability to keep creating really big eruptions. More likely is we’ll have more of these big lava flows coming out… using up what magma is down there. But nobody can tell you for sure. Is there enough magma down there to create a supereruption? A supereruption again is one with a thousand cubic kilometers of erupted material. To get a supereruption you have to get all the melt into one place. The magma chamber is like a sponge. It’s crystals or rock with the pores filled with the melt. But you can’t erupt a magma unless it’s more than about 50% melt. Most volcanic eruptions are about 75% melt. All of the images that we have through the seismic tomography tend to predict that there’s 10 to 15% melt on a broad basis. We can’t really image small areas. So it’s possible that there’s some highly molten areas down there, but they’re probably not enormous. We don’t think there’s a big enough area (volume) with highly melted regions that could create one of these big eruptions, but there could be smaller areas that could erupt if the right circumstances forced it.
Has the magma chamber gotten bigger? This is something that came into the news recently. Our colleagues at the University of Utah have redone the tomography for the magma chamber beneath Yellowstone. And that’s something that’s constantly going to happen, ’cause we’re always getting better data. We have new equipment in the ground. We’re able to put things in better places so we have better coverage. And so they were able to find that compared with the last time that they did the tomography they were able to see the magma better. So they got two-and-a-half times more magma than the previous time.
The number is still consistent with what we see, the size of the caldera, the amount of heat coming out of Yellowstone. So it’s nothing shocking. It means that we can do our job better than we could earlier. And five years from now there’ll be a new study that comes out that figures thing out a little bit better. That’s the way science proceeds. Will we know it’s coming? This is a tough one to say, because nobody’s ever seen a supereruption. The last one was 26,000 years ago… and they took really lousy notes. We have seen some relatively large eruptions but the last big eruption on Earth, around a tenth of the size of one of these was the Tambora eruption in 1815.
It caused the “Year without a Summer.” And that was a very big eruption and would cause a lot of havoc, even though it’s only a tenth of the size of one of these Yellowstone eruptions. We don’t have a lot of data on exactly know what happens before them. We do know what happens before smaller volcanoes erupt and we know what we think would happen at Yellowstone. And we also have watched what’s happening at Yellowstone for a hundred years. We know earthquakes happen all the time. We know that ground deformation happens all the time. They really have to happen on a bigger scale. If we see earthquake swarms, they’re going to be big and they’re going to have some larger earthquakes to break the rocks up so that we can get magma to the surface.
You’re going to see ground deformation in the same area that you’re seeing the earthquakes. That’s something we rarely see, especially significant amounts of ground deformation, on the order of meters of uplift, in a year or so, to show that something’s really moving. You’re going to see increased gas emissions, and that’s going to be obvious no matter what techniques you have. And if magma is getting near the surface it’s going to cause steam explosions. Magma hits a boiling aquifer system, boiling groundwater system, it’s going to explode. And so you’re going to see all of those things happening at the same time. The last time there was a big eruption at Yellowstone, 640,000 years ago there was a whole series of lava flows that came out around the periphery of the caldera before the big eruption.
Maybe ten thousand years before. Here we haven’t had anything for 70,000 years. I’m not saying for sure we’re going to get the exact same thing, and that we can all not worry about it. It just goes to show you that a lot needs to happen before a big eruption. So that’s all I have prepared, except to say that we do have a really good website. It has lots of articles, provides a lot of information on what’s going on at Yellowstone, all the data that you might want to see. It’s really easy to find. You can just google YVO. We also have some fact sheets, these are downloadable, and they’re pretty nice six-page and four-page glossy brochures that you can print out for yourself. And they talk about all of the things that I’ve brought up today. .