Monthly update of activity at Yellowstone Volcano for July 2021

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During July, Yellowstone caught everyone’s attention with 1,000+ earthquakes located in seven distinct earthquake swarms. The largest swarm occurred beneath Yellowstone Lake and had 764 earthquakes, the largest of which was a Magnitude 3.6. While this seems like a lot of earthquakes, it is not the most Yellowstone has experienced in any given month and the volcano alert level remains unchanged.

The earthquake swarms are not caused by magma. The earthquakes occurred on existing faults, triggered by increased pore pressure from the extra groundwater that accumulated as the snow melted. One of the things we look at to see if magma was involved, is changes in ground deformation. We haven't seen any changes in ground deformation during the month of July that has been outside multi-year trends.

Yellowstone Volcano Observatory scientist-in-charge Mike Poland discusses activity in Yellowstone in this monthly update recorded near Solitary Geyser, within Yellowstone National Park.


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Length: 00:06:42

Location Taken: US

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Video edited by Liz Westby


Hi everybody, I'm Mike Poland, the scientist-in-charge of the Yellowstone Volcano Observatory, and this is the monthly update for August 1st of 2021. 

Today we're coming to you from the Upper Geyser Basin in Yellowstone National Park, not too far from Old Faithful. This is Solitary Geyser behind me, just on the hill above Old Faithful, and Solitary has sort of an interesting history. For a long time, it was just a pool, very gentle, calm pool, but in the 1930s, water was actually piped away from Solitary to feed, of all things, a thermal swimming pool down in the Old Faithful area. Now when that water was drawn off, it changed the dynamics of the geyser and actually, the pool started to erupt infrequently, just small eruptions every few minutes. Now, after a few years of this, of course, the pool was deemed not a great idea, and the pipeline was removed and the water level was restored, but Solitary's activity continued. Even to this day, we see small eruptions, just a few feet high every few minutes here, at Solitary. 

Alright, well, let's talk about what happened during the past month in terms of volcanic and earthquake activity in Yellowstone. 

Well, it was a doozy of a month for earthquakes in Yellowstone during July. The University of Utah seismograph stations, they maintain and monitor the Yellowstone Seismic Network, located over 1,008 earthquakes during the month, and they're not even done counting, yet. They still have some small earthquakes that they need to review that may have been missed by the computer. Now, most of these earthquakes occurred as part of seven distinct swarms. Five of those swarms occurred here in the area between Hebgen Lake and the Norris Geyser Basin. There was a small swarm also down here, on the Pitchstone Plateau. All of these swarms were anywhere between one and three or four dozen events, magnitude one to two, so fairly typical swarms for the Yellowstone region. The big swarm of the month was this one right here, right beneath the center of Yellowstone Lake. This one had at least 764 earthquakes, probably a few more once the catalog finally gets completed. The largest was a magnitude 3.6 and that occurred on July 16th when most of the earthquakes of this swarm took place. 

Now this may seem like a lot and it is. The month was quite a doozy for earthquakes, but it's not actually the most we've seen in any given month. Back in June of 2017, we saw over 1100 earthquakes, mostly due to a swarm that occurred here, in the Maple Creek area. It lasted three months and had over 2400 earthquakes. And in 1985, there was a much larger earthquake swarm or more than 3,000 events located in the Madison Plateau area. And this also isn't, by far, the largest earthquake we've seen in Yellowstone. The 2017 swarm had a magnitude 4.4. Back in 1975, there was a magnitude 6.1 event that occurred in the Norris Geyser Basin area. And of course in 1959, there was a magnitude 7.3 that occurred just off the western boundary of the park in Hebgen Lake. So this is a really impressive earthquake swarm, no doubt about it, and a big month for earthquakes. But is not out of the range of what Yellowstone has done in the past. 

And this is also not something that's caused by magma moving around. These are existing faults that are moving, sometimes sort of goosed by increases in pore pressure, that's groundwater from snow melt that's getting into these faults and causing them to trigger. Now, one of the things we might look at to see if magma might be a cause of these sorts of earthquakes is ground deformation, and we haven't seen any changes in ground deformation during the month of July. 

This is vertical deformation over the last two years at the White Lake GPS station, which is on the east side of the caldera on the Sour Creek resurgent dome. Each one of these blue dots represents one day of data and you can see it goes back to August of 2019. Downward trends are subsidence and upward trends are uplift. And you can see the overall trend is one of subsidence over this two-year span of about one to two inches per year or so, maybe three centimeters per year. Each summer, though, we see these small pauses or even slight reversals in that subsidence trend and that's due to this groundwater recharged from snow melt. So we've seen the same changes pretty much every summer over the last several years. What we're seeing now is very much akin to what we saw last year and the years past. So we haven't seen any significant changes in deformation that might suggest that something different was happening at Yellowstone. 

If we look over at the other side of the caldera, this is the west side of the caldera and the Mallard Lake resurgent dome near Old Faithful. We see the same trend of subsidence of an inch a year or so with a slight pause now, just as we saw back in the last summer due to groundwater recharge. And we see a much better dataset here, since September of last year, because, due to some fire danger nearby, some of the trees near the station were cleared and that allowed a much cleaner signal at this particular GPS station. 

In the Norris Geyser Basin, we also haven't seen many changes in deformation. Now, Norris had been uplifting from 2015 to 2018 and subsided a bit, as you can see here, in late 2019, and since early 2020, there really hasn't been much in the way of changes at all. We're seeing a slight increase in the level of the ground by about a centimeter or so over the last few months, but we saw a similar change here, in the summer of 2020, so it's likely that this is related to groundwater, as well. 

So overall, in the Yellowstone region, we're not seeing changes in deformation associated with the seismicity. So yes, there were a lot of earthquakes, but they're related to motion on pre-existing faults, perhaps goosed by the groundwater that is increasing in pressure because of the snow melt and the groundwater increasing in volume because of that melt. 

Finally now, turning to Steamboat Geyser, we have seen one eruption during the month of July, and that was right here, on July 8th. All of this sort of variability in the temperature record of the Steamboat runoff channel is due to minor eruptions. Then we had the major eruption, right there, on July 8th, and then we went back to these daily temperature variations. And we haven't seen much of a change in these daily variations, so it very much seems like Steamboat might be, to pardon the pun, running out of steam. We have seen many fewer eruptions this summer than we have each of the past three summers. And this is what Steamboat does, it goes through cycles of more eruptions and less. So it appears that we may be coming to an end of the current cycle of Steamboat eruptions. We'll have to see how the activity holds over the remaining part the summer. 

Well, that does it for the monthly report for the Yellowstone Volcano Observatory. Now remember, if you have any questions, you can feel free to email us anytime at YVOWebTeam, that's all one word, Stay safe, stay healthy and we'll see ya next month, bye-bye.