WEBVTT

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What geologic hazard is most likely to occur

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in the Yellowstone region on human timescales?

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Spoiler alert, it has nothing to do with a volcano.

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We'll answer that question in this August, 2023 update,

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from the Yellowstone Volcano Observatory.

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If you enjoy this video,

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please remember to like and subscribe down below

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so that we can bring you more content

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like this in the future.

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A common misconception is that a volcanic eruption

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is the most likely thing to occur in the Yellowstone region

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on the timescale of a human life.

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There have been some huge eruptions.

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631,000 years ago was the formation of Yellowstone Caldera.

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That was a massive explosion,

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but those only happen about once or twice per million years.

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Slightly more common are lava flows.

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There have been a few dozen of those

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in the last million years,

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but the last one was 72,000 years ago,

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so even that isn't so common.

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But strong earthquakes,

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those happen once or twice per century.

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We're standing next to the actual fault scarp

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that formed on August 17th, 1959

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in a magnitude 7.3 earthquake, the Hebgen Lake earthquake.

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This is the largest earthquake still ever recorded

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in the Intermountain United States.

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At the time, before that earthquake occurred,

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these two bits of ground were level,

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and they split apart during that great event.

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We can actually put our hand

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directly on the fault that ruptured.

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The quake struck just before midnight.

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It caused a major landslide in the Madison River canyon.

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50 million cubic yards of rock, mud,

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and debris came down the south side of the canyon

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and went halfway up the north side.

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It inundated camping areas and caused over two dozen deaths.

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It also dammed the Madison River,

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resulting in the formation of what is now known

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as Quake Lake. It drowned trees,

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it floated cabins off their foundations.

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It threatened additional flooding

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if the debris dam were to collapse.

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Now, the Army Corps of Engineers stabilized the dam

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and the lake level stabilized,

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but you can still see today the drowned trees

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in the margin of the lake and cabins

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that were dropped in a field

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as the lake level dropped and stabilized.

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The shaking also caused quite a bit of damage to roads

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and infrastructure, and it impacted the hydrothermal system

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in Yellowstone National Park.

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Within 24 hours, at least 289 springs erupted as geysers.

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160 of those had no recorded previous eruptions.

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Hundreds of springs became cloudy with stirred up debris

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and some new thermal areas formed

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as cracks allowed new pathways for heat and water.

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It caused Old Faithful's eruption interval

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to become a bit erratic and ultimately the average interval

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between Old Faithful eruptions increased by several minutes.

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Yellowstone sits within a part of the Western US

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that's very active tectonically.

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There are large faults everywhere,

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like the Teton fault at the base of the Teton range.

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And these are all capable

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of magnitude six to seven earthquakes.

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There was even a magnitude six earthquake

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within Yellowstone National Park in 1975.

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These events will happen again in the future,

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typically at a rate of one or two per century.

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So strong earthquakes,

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these are really the most important regional scale hazard

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on human timescales in the Yellowstone area.

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It was another quiet month of earthquakes

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in the Yellowstone region.

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The University of Utah Seismograph Stations

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located just 88 events during July.

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The largest was a 2.2

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just north of Canyon Junction on July 25th.

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There was also one swarm of 12 earthquakes

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located just to the northeast of West Yellowstone

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that occurred during July 10th to the 13th,

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the largest, a magnitude 1.5,

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and it was part of this band of seismicity

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that extends from Hebgen Lake

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into the north central area of the park.

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So pretty average month as far as earthquakes go.

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Turning now to ground deformation.

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This is vertical deformation for the past two years

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at the White Lake GPS station

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on the east side of the caldera.

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Each blue dot is one day of data.

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Downward trends indicate subsidence

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and upward indicate uplift,

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and the overall trend is what we've seen since 2015,

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and that is subsidence of a few centimeters,

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about an inch or so every year.

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It's interrupted during the summer months

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by a pause in the subsidence or a little bit of uplift,

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and that's caused as groundwater gets recharged

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by snow melt and runoff, as that percolates into the ground,

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sort of puffs the ground up like a bit of a sponge.

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You can see that uplift here in 2022 and again in 2023.

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So seasonal uplift, interrupting this overall trend

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of subsidence in the caldera.

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Finally, looking at the tallest geyser in the world,

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Steamboat Geyser, this is the temperature measured

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in the geyser's outflow channel,

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and all of this sort of spiky behavior

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is minor geyser activity

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that's superimposed on daily temperature variations.

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No major eruptions during the month of July for Steamboat.

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So the total number of major eruptions

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for the year remains at five.

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Well, that does it for the August, 2023 update

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of the Yellowstone Volcano Observatory.

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Please remember to like and subscribe,

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and if you have any questions at all,

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feel free to email us at yvowebteam,

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that's all one word, @usgs.gov.

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We'll see you next month and until then,

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stay safe and stay healthy.

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Bye-bye.

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(gentle music)