Yellowstone volcano: Why mega earthquakes are the ‘greatest hazard’ and NOT eruptions

Although Yellowstone volcano’s last three eruptions were cataclysmic, large earthquakes are a much more frequent threat. Yellowstone last erupted about 640,000 years, 1.3 million and 2.1 million years in events dubbed super-eruptions.

But the last major earthquake struck Yellowstone only 61 years ago and each year, the national park in the northwest US is rocked by thousands of smaller quakes.

Yellowstone averages about 1,500 to 2,000 earthquakes a year, making it one of the most seismically active hotspots in the US.

Because of this seismicity, anyone fearing another Yellowstone eruption should reconsider what the real “greatest geological hazard” is.

The USGS said in its weekly Caldera Chronicles: “In a previous YYC article, we discussed the 1959 M7.3 Hebgen Lake Earthquake that occurred just west of Yellowstone National Park.

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“Because of this earthquake and the thousands of others that we record each year, we know that the area is seismically active and capable of producing large, damaging earthquakes.

“In fact, because of their rate of occurrence, large earthquakes represents one of the greatest geological hazards in the area, much more so than a volcanic eruption.”

When the Hebgen Lake Earthquake struck on August 17, 1959, seismometers peaked at magnitude 7.3

The earthquake struck just 6.5 miles west-northwest of West Yellowstone in Montana.

At least 28 people were killed by the disaster, which triggered a large landslide in Madison Canyon.

The landslide is estimated to have released about 50 million cubic yards of rock, mud and debris, partially burying the nearby Rock Creek campsite.

Large earthquakes represents one of the greatest geological hazards in the area

US Geological Survey (USGS)

The landslide also backed up Madison River, blocking off its flow and creating Earthquake Lake.

However, of the thousands of earthquakes that rock Yellowstone every year, most are too weak to be noticed.

The USGS estimates only about five quakes were felt each year in the last decade.

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Most of the earthquakes are in the range of magnitude 0 to magnitude 2.

The largest earthquake in recent years was a magnitude 4.8 event near Yellowstone’s Norris Geyser Basin in 2014.

The USGS said: “So while there is always a chance that visitors to Yellowstone will feel an earthquake, the chances increase if there is a significant swarm occurring.”

Reports of earthquakes in the Yellowstone region date back all the way to 1871, and the first expeditions into this wild part of the US.

When Ferdinand V. Hayden led a team of researchers into Yellowstone that year, the expedition felt an earthquake while camping on the north shore of Yellowstone Lake.

The expedition recorded their experience on August 1, 1871, writing: “This morning about one o’clock we had quite an earthquake.

“The first shock lasted about 20 seconds and was followed by five or six shorter ones.

“Duncan who was on guard, says the trees were shaken and that the horses that were lying on the ground sprang to their feet… We had three shocks during the morning.”

The USGS said: “Remember – Yellowstone is earthquake country, and people should be prepared for the consequences of damaging events.”

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