Yellowstone: where did all the ash go?

A post by Chris Rowan A couple of weeks ago, I showed the trough excavated through the mountains of the western US by explosive caldera eruptions above the migrating Yellowstone hotspot.

Path of the Yellowstone hotspot

The chain of caldera left in the wake of the Yellowstone hotspot.

These eruptions excavated a lot of rock: the most recent eruption of the Yellowstone caldera, 600,000 years ago, pulverised 1000 cubic kilometres of crust into ash and threw it into the atmosphere. When it finally settled to the ground again, a lot of it had drifted or been blown hundreds of miles away from Yellowstone. It settled in Kansas.

Lava Creek Tuff exposed near Desoto, Kansas. Photo: J. S. Aber

It also settled in Utah (apologies for the rather distant and grainy photo).

Cliff exposure of Lava Creek Tuff (LC) in Fisher Valley SE Utah. Source: Colman et al. (1986)

And some floated as far as Western Iowa.

Lave Creek Tuff, exposed in Western Iowa. Source: Roy et al. (2004)

In fact, 0.6 million year-old ash layers, with a distinctive mineral composition that links them to the same eruptive event and to the Yellowstone caldera, can be found in sequences over a sizeable proportion of the continental US. Collectively, this unit is known as the Lava Creek Tuff (sometimes referred to as the Pearlette ash in older literature).

Distribution of Lava Creek Tuff in continental United States. Orange dots - ash layer outcrops pictured above.

This is another way that the almost unimaginable scale of a large caldera eruption compared to the kind of volcanic activity we have direct experience with can be highlighted. The ash from the Eyjafjallajokull eruption earlier this summer was dispersed more than 1000 km from Iceland by strong winds, totally disrupting air travel as it went; but the ash that settled on the ground in Western Europe was, at most, a light dusting – it would be generous to say half a millimeter. As the outcrops above demonstrate, an equivalent distance (1000 kilometres) from Yellowstone, the Ash Creek tuff is about half a meter thick – one thousand times thicker. Three orders of magnitude. Somewhat eye-opening, don’t you think?

On the plus side, the Lava Creek tuff, and similar widely distributed ash layers from earlier eruptions of the Yellowstone caldera chain since 16 million years ago, provide a set of useful correlative markers between sequences in widely seperated sedimentary basins in the US – igneous index fossils, if you will.

Categories: outcrops, volcanoes
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Comments (11)

  1. Lab Lemming says:

    You say, “with a distinctive mineral composition that links them to the same eruptive event and to the Yellowstone caldera”.
    What are the distinguishing mineralogical features?

    Another factor you need to take into account is conventional erosion of the topographic high produced by the thermal uplift. Yellowstone was glaciated during the LGM, and there are big moranes all over the area (e.g. the dam for Lake Jackson) which show that much of the material removed from Yellowstone was taken by ice. In addition, there has been considerable fluvial erosion in the ~14,000 years since deglaciation, as can be seen from the significant incisions such as the grand canyon of the Yellowstone. Once the continental plate moves past the hotspot, it will cool and drop back down to its original elevation, minus the material removed by erosion.

    • Passerby says:

      Answered your question on unique chemistry, over at the Eruptions blog, Open Thread #2.
      A comment response to my post at Eruptions noted the ash deposition you mention is found along the lower Mississippi River by Matt Totten. I added a reference that mentions the Yellowstone Volcanic deposits in drilling logs.

      If you don’t mind a longer read, one of his student’s thesis discusses the chemical signature of Yellowstone caldera eruption ash found offshore (LA), in the Gulf of Mexico. Although erosional perturbation in the reworked deposits has altered the chemistry, it’s a nifty read anyway.

  2. pirata says:

    fyi… current theory suggests that the continent passed over the stationary hotspot, not the other way. as you state it above, “migrating Yellowstone hotspot” could be misleading to some readers…

    otherwise, a more distinctive global marker is the huckleberry ridge tuff, erupted ca. 2 ma from another yellowstone eruption. this tuff also preserves a geomagnetic polarity reversal. the reversal has been identified in numerous deep sea cores. it’s sometimes referred to as the huckleberry event, but i’ve also seen it as reunion-II, with a slightly older age. either two excursions, or bad ages on one of them. in all, it looks like the jury’s still out on this one.

  3. Chris D. says:

    I just did a quick calculation:

    The distance of crustal migration over the hotspot (or hotspot migration under the crust) that took ~16 million years corresponds to around 700 kilometers.

    A distance of 700 kilometers on the Atlantic ocean spreading ridge corresponds to ~50 million years of isochron data.

    That’s a bit of a mismatch of distance over time. Are there any explanations for this disparity? I assume that there is a lot of crustal shortening in between, but is the difference taken up by the continent or the ocean floor?

    Great post, anyways.

    • Chris Rowan says:

      You’re actually comparing two different things. The spreading at the North Atlantic ridge is a manifestation of the motion of the North American plate relative to the Eurasian plate (and vice versa). The Yellowstone hotspot is recording the motion of the North American plate relative to the mantle (assuming the plume is relatively stationary). They will only be the same if the Eurasian plate is also fixed relative to the mantle, which is not the case.

  4. Lab Lemming says:

    More resources:
    summary of the Snake River plain geology:

    And a paper describing how hotspot dome migration effected the continental divide, drainage patterns, and stream capture:

  5. Brian Olson says:

    We were able to identify a distinctive purplish tuff, which is found consistently throughout southern Orange County, CA in the Monterey Formation. Via tephrachronology, it was determined this was Yellowstone tuff, from the Cougar Buttes eruptive series, dated at about 11.5 Ma (I don’t remember the exact age but it was 11 point something Ma). I believe there is a nice paper in Geology, which summarizes the Tertiary eruptive history of the Yellowstone area.

  6. Brandon says:

    Would this be the same ash that was deposited in the Badlands of South Dakota? I am just an incoming Geology major, so I apologize if the answer is obvious, it just appears that the Lava Creek map corresponds to the general region. I know that the ash in the badlands was laid down in the Oligocene (much earlier than the Lava creek bed map). Could this have been from a much earlier event? Thanks for the great post.
    Brandon; Southern Indiana

  7. Brandon says:

    Here is some additional information I found via USGS.

    *”As the Oligocene Epoch drew to a close, volcanoes to the west and southwest ejected huge volumes of ash into the atmosphere. Borne eastward by the winds, the ash fell and became the whitish layer near the top of the Badlands formations.”

    * about halfway through the webpage

    • pirata says:

      probably not yellowstone-related. the thought is that the hotspot originated sometime around 17mya, near the idaho-oregon-nevada border, much later than the end of the oligocene. there was the challis volcanic event in central idaho during the eocene, older than the south dakota deposits. i’m not quite sure of the origin of the oligocene south dakota ash fall deposits, but my best guess is that they are likely to be related to john day and central oregon eruptions. but i can say with certainty that they are not from any of the snake river plain-yellowstone hotspot eruptions.

      link to john day: