Monthly update of activity at Yellowstone Volcano, May 1, 2023

Hi everybody, I'm Mike Poland, the scientist in charge of the Yellowstone Volcano Observatory. This is the monthly update for May 1st of 2023. Coming to you from the warehouse at the Cascades Volcano Observatory, where we're getting ready for summer fieldwork, deploying all kinds of new monitoring sites, that will include some work in Yellowstone as well. Now May is traditionally the start of the field season as snow levels go down, although that might be a problem this year. There is a lot of snow still at Yellowstone from a really extreme winter. But we're hoping to do a lot of work in Yellowstone, like the traditional deployment of semi-permanent GPS stations throughout the park. We do that to densify the GPS network.

There will also be studies throughout the year on hydrothermal explosion craters where water flashes to steam and creates craters like Mary Bay and Turbid Lake on the north side of Yellowstone Lake, also Pocket Basin in the Lower Geyser Basin. We'll be looking at the deposits created by the last big caldera-forming eruption in Yellowstone, the Lava Creek Tuff, which formed 631,000 years ago. And hopefully we'll be installing a new monitoring site in the Norris Geyser Basin, and that's part of the Yellowstone Volcano Observatory monitoring plan. Now we have the whole region very well covered in terms of low level seismicity and ground deformation, but we need to do a better job of looking at what's happening in the Geyser Basin specifically. We'll be installing a new site in Norris Geyser Basin, sort of away from the public areas. We try to be good stewards of the landscape in Yellowstone. And this new site will be able to locate small earthquakes, detect ground deformation in the Geyser Basins, and also listen to the Geysers.

A microphone will be able to detect low-frequency acoustic energy. And hopefully this sort of site will be a blueprint for things we can do later on in some of these Geyser Basins that will help us better understand how the Geyser systems in Yellowstone work. Alright, well, that's what we have planned for this summer. Now let's talk about what happened over the last month in Yellowstone. During the month of April, the University of Utah seismograph stations, which operates and analyzes data from the Yellowstone Seismic Network, located 168 earthquakes in the Yellowstone region. This is sort of normal background seismicity for the area. The largest event of the month was a magnitude 2.

5 earthquake that occurred on April 15th below the eastern side of Shoshone Lake. And this was part of a swarm of about 50 earthquakes that occurred in mid-April. Another swarm of 33 earthquakes occurred near West Thumb towards the end of the month. Aside from these two swarms, seismicity was more or less distributed throughout the region with the usual belt of more abundant earthquakes between Hebgen Lake and the area of Norris Geyser Basin. This is the most seismically active part of the park, probably thanks in part due to the 1959 Hebgen Lake earthquake and the stress changes that it caused in this region. Looking at deformation, we've seen a continuation of the trends that have been ongoing since 2015. This is vertical deformation at the White Lake GPS station on the east side of the Caldera, the Sour Creek Resurgent Zone.

Each one of these blue dots is one day of data, and this plot spans the last two years. Downward trends indicate subsidence, and upward trends indicate uplift. We're seeing these continued subsidence trends, especially during the winter months. There are small interruptions in that trend, a slight amount of uplift during the summer months, and this occurs as snow melt recharges the groundwater system and the water sort of soaks it up like a wet sponge. But once the summer ends, we get back to subsidence. And since October, we've seen about 3 centimeters, slightly more than 1 inch, of subsidence on the east side of the Caldera. If we go to the west side of the Caldera, the Mallard Lake Resurgent Dome near Old Faithful, we see much the same story.

Small subsidence over the last several years, interrupted during the summer months by a small amount of uplift. And just like over on the east side, the west side shows about 3 centimeters of subsidence, slightly more than 1 inch since October. There hasn't been a whole lot of deformation in the area of the Norris Geyser Basin. This is vertical deformation in the Norris area over the last two years. There's this big excursion here towards the end of 2011, and that's from a winter storm that covered the GPS antenna in snow and ice. And you can see some similar effects here towards the end of 2022 and the beginning of 2023. But like all of the other stations, we're seeing just a very slight amount of subsidence in the Norris area, about 2 centimeters of subsidence since October.

And finally, looking at everyone's favorite geysers, Steamboat Geyser, the tallest active geyser in the world. Unfortunately, the seismometer and the temperature monitoring network are still down. That's something we hope to repair in the coming month as fieldwork becomes possible in the Yellowstone area. But we can still look at Steamboat activity using the stream gauge that is recording all of the water and that leaves the Norris Geyser Basin area. And that's located at Tannulus Creek right before it joins the Gibbon River. This is stream flow through that area. There's a real spike here in mid-April due to heavy precipitation.

But there are no obvious spikes associated with Steamboat Geyser eruptions. To get an idea of what those look like, let's go back to January, the last two confirmed Steamboat eruption. There's one right there in early January and another one right there in late January. And those sorts of spikes just are nowhere to be seen in this record. So it looks like Steamboat has remained quiet since January with only two eruptions so far in 2023. Well, that does it for the monthly update for May 1st. Now, remember, if you have any questions at all, you can feel free to email us anytime.

Our address is yvowebteam, all one word, at usgs.gov. Until next month, stay safe, stay healthy. We'll see you next time. Bye-bye.

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