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What did the seismology equipment record during the record flooding in Yellowstone National Park? – Daily Montanan

['Jamie Farrell', 'More From Author', '- June']

Date: 2022-06-28 00:00:00

After the news of the devastating flooding that affected northern Yellowstone and southern Montana spread, people started asking if all this would affect the seismicity in and around Yellowstone. The answer to that question is that there probably wouldn’t be much of an effect.

However, that doesn’t mean that the network of over 40 seismometers in the region didn’t record the actual flooding. In fact, many stations saw increased amplitudes of ground shaking as the flood waters rose. This isn’t evident in the webicorders that you can see online; one must do some “processing” to actually see the signal from the flooding, as the amplitude is relatively small and is overprinted by the much larger signals from things such as wind, trees, traffic and background noise. This processing involves filtering the data to emphasize frequencies between 1–1.5 Hz, which is where the flooding signals are most evident. Two seismometers that are close to rivers that were most affected by the increased snowmelt and precipitation were station YSB near Soda Butte in northeastern Yellowstone and station YUF near the Upper Falls of the Yellowstone River.

Station YSB is about 0.3 miles from Soda Butte Creek. Soda Butte Creek is a major tributary of the Lamar River. There is a USGS streamgage on the Lamar River just upstream from where it flows into the Yellowstone River. Data from this streamgage show that prior to June 12, the Lamar River was at roughly 8,000–9,000 cubic feet per second and was showing daily increases due to warm daytime temperatures that were increasing the snowmelt to the river. Starting late on June 12 and early on June 13, however, there was a strong positive spike in the discharge, culminating in a peak discharge of around 21,000 cfs on June 13. At the same time, the overall amplitude of the seismic signal at station YSB increased from a peak of about ±5 counts to ±15 counts (counts are the value of the amplitude of the raw seismic data that come out of the seismometer). This is due to the increased flow of the river causing vibrations in the ground that then travel through the earth and were recorded at the nearby seismic station.

Station YUF is about 0.6 miles from the Upper Falls of the Yellowstone River. The closest streamgage is actually where the Yellowstone River exits Yellowstone Lake and starts to flow north. Unlike at the Lamar River, the gage at the outlet of Yellowstone Lake recorded a steady increase in discharge with time, although the rate did increase on June 12–13. Overall, the discharge increased by a total of about 1,200 cfs from June 11–16. The reason why there isn’t a clear spike at this gage (like there is at the Lamar River gage) may be because this gage is at the outlet of Yellowstone Lake, and a large increase in flow is somewhat buffered by the lake itself. However, the seismic signal at station YUF is similar in that the amplitudes increase from a background of around ±250 counts prior to June 12 and peaking at ±500 counts on June 13. Unlike the seismic signal at YSB, the seismic amplitude doesn’t go back down to pre-flood amplitudes but stays at around ±375 counts through June 16. This is because unlike the Lamar River, the discharge in the Yellowstone River leveled off at higher values (~4,600 cfs) instead of dropping down to pre-flood values. Again, this could be because of the influence of Yellowstone Lake.

So even though we haven’t observed increased seismicity due to the increased amount of water, the seismic network in Yellowstone clearly recorded the signals related to the devastating flooding in the area through the increased “noise” generated by the rivers themselves. And even though we wouldn’t necessarily expect any effects on the seismicity, the increased amount of water could have impacts on the hydrothermal system. Case in point may be Steamboat Geyser, which erupted on June 20, 2022, just under 10 days and 4 hours since its previous eruption. This was the shortest time between eruptions of Steamboat Geyser since April 2021. Did the increased precipitation have something to do with the relatively short interval? Time will tell…

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from Jamie Farrell, assistant research professor with the University of Utah Seismograph Stations and Chief Seismologist of the Yellowstone Volcano Observatory.

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