What happened at the end of the Eocene?


Southern margin of La Garita Caldera, Colorado, from USGS http://pubs.usgs.gov/imap/i2799/photos/8-S_LG_caldera_margin.html

Southern margin of La Garita Caldera, Colorado, from USGS

I have a long standing interest in large discontinuous events in history – essentially things that go “boom” – and their impact on geology, living things, and the course of history – how these events happen, what makes them happen, and why they happen.  This interest has led me to volcanoes and their eruptions.  It has also led me to look into impact events that wipe out types of life and significantly rearrange the landscape.

A lot of the causes overlap in time or take place so far in the distant past that it is difficult to figure out which caused which.  We also need to remember that volcanic activity is for most intents and purposes continuous, though it does wax and wane in intensity over the millions of years as driven by plate movements, rifting, collisions and mantle plume / hot spot activity.

Fish Canyon Tuff – La Garita Caldera, Colorado

Fish Canyon Tuff – La Garita Caldera, Colorado

To me, the most important questions are what causes the discontinuity in climate?  What causes multiple extinction events?  What causes sufficiently large insults to the environment that lead to mass extinctions of entire species and significant long-lived change in climate?  Usually, the Flying Finger of Fate is pointed at a single cause which may be volcanic eruptions, impact events, close supernovae explosions, methane blooms, massive global heating, massive global cooling, aliens, etc.; none of which we have ever see in real time.

What I am wondering is that while volcanic eruptions place significant stress on the environment, cooling things down for years to decades or longer, perhaps they need something else happening at nearly the same time, something big to trigger an extinction event.  A few examples follow.

Graphic showing location of proposed Shiva impact structure.  Unable to find original paper.  Image was posted at link below: http://rajgire.wordpress.com/2012/03/13/shiva-crater/

Graphic showing extinction events, large igneous province outbreaks and massive climate shifts. From Large Igneous Provinces Commission, August 2013 LIP of the Month http://www.largeigneousprovinces.org/13aug

A Few Extinction Events

The Cretaceous – Tertiary boundary 65 million years ago marking the end of the dinosaurs is thought by some to be linked to the Deccan Traps in India.  There is a roaring argument about which caused which, as there are a pair of impact structures identified dating to around that time – the Chixculub crater in the Yucatan and Shiva off the west coast of India.  Regardless of the resolution of the argument, it appears both volcanism and impact events were involved.  http://news.nationalgeographic.com/news/2009/10/091016-asteroid-impact-india-dinosaurs.html

Graphic showing location of proposed Shiva impact structure.  Unable to find original paper.  Image was posted at link below: http://rajgire.wordpress.com/2012/03/13/shiva-crater/

Graphic showing location of proposed Shiva impact structure. Unable to find original paper.

The Permian – Triassic extinction event which wiped out over 90% of marine species and over 70% of all vertebrate life on dry land some 250 million years ago is another.  It is mostly blamed on the eruptions from the Siberian Traps that caused a massive rise in global temperatures.  Some have suggested an impact component with a couple candidate large crater structures suggested.  But if the Traps erupted over an extended period of time, several millions of years, as have been suggested here, then the impact events punctuate and immediately push an already stressed environment into failure.  Causation on this is even less well known, but volcanism is clearly involved.  Impact events may also be involved but several other mechanisms have been proposed like mass release of methane (greenhouse gas) into the atmosphere as the planet heated up.  http://www.space.com/2452-giant-crater-tied-worst-mass-extinction.html

There also seems to be an antipodal effect where volcanic activity or mantle hot spot is found on the other side of the globe from an impact structure that Geolurking wrote about last year or so.  Hot spots may end up being fossil evidence of impact events into the ocean.  http://www.mantleplumes.org/WebDocuments/Antip_hot.pdf

The gradualist geologic view of the world has changed over the last century, with grudging acceptance that large, relatively instantaneous catastrophic events have driven the history of life on this planet.  Not having seen one actually happen (and I don’t want to), we are left with the scientific method of comparing observations and theory against models while building them up and tearing them down.

Impact events, even relatively recent ones in the last few thousand years, are difficult to pin down unless they are really, really large.  70% of the surface of the planet is ocean bottom, crustal plates that have a finite lifetime and are either subducted into oblivion or crunched up into mountains when trapped between two impacting continents (Himalayas).  We can extrapolate the flux of inbound bodies based on the number of craters known on the continents, but this is at best a low estimate as it does not consider airburst events (Tunguska, Chelyabinsk) which apparently regularly take place.  And sometimes those airburst events get very, very big.

There is a group of people investigating the possibility that a comet storm caused a continental level extinction event over North America some 12,000 years ago – think tens of thousands of Tunguska sized airbursts raining down over North America in the course of a few hours – plunging global temperatures back to ice age levels for over a thousand years (Younger Dryas).  There has been no volcanic component yet proposed for the event outside a suggestions by a Mexican geologist that “trap-door” calderas in Mexico were responsible for the presence of ignimbrites in Mexico and the Southwest US.  An alternate view based in experience with what happens under nuclear fireballs believes the ignimbrites were formed by multiple airbursts and the melted, glazed rock is the remains of airburst created density currents.  http://cosmictusk.com/first-harvard-now-dartmouth-evidence-identified-for-younger-dryas-impact/

With this background in mind, I would like to explore for a bit the minor extinction event at the end of the Eocene, some 33 million years ago.  The event is marked by large impact craters, most notably one centered on the mouth of the Chesapeake Bay in North America, and an outburst of caldera activity in what is now Colorado.  It also marked a downward shift in global temperatures toward the ice ages we now endure.  This is in no way a comprehensive exploration, but more a way to publicly scratch my head.  Something clearly happened.  The question is what and how?


Fish Canyon Tuff – From USGS Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado http://pubs.usgs.gov/imap/i2799/

Fish Canyon Tuff – From USGS Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado.

There was a caldera outbreak in Colorado some 40 – 25 million years ago.  This outbreak spanned the Eocene extinction event.  Whatever impact on climate due to the eruptions was exacerbated by impact events around the 33 million year point that were sufficient insult to change climate and wipe out species.


Activity in the San Juan Volcanic Field started some 40 – 35 million years ago and for the first 5 million years was dominated by andesite, rhyolite and mafic quartz latities.  Height of the activity was some 35 – 30 million years ago, at the time of the Eocene event.  Around 30 million years ago, the activity shifted to a predominantly ash-rich, pyroclastic output which tailed off over the next several million years.


There is a paper or two that suggests the caldera outbreak was related to a chunk of the subducted Farallon plate that either broke off or traveled parallel under the North American continent rather than diving into the mantle to melt.  As the continent stretched a little bit with the uplift of the Colorado Plateau and the failed Rio Grande rift, this allowed the melt to rise to the surface and eventually erupt.


Snowshoe Mountain (resurgent dome) within Creede Caldera, Colorado (image behind paywall) http://elements.geoscienceworld.org/cgi/content-nw/full/4/1/17/FIG4

Snowshoe Mountain (resurgent dome) within Creede Caldera, Colorado (image behind paywall)

And erupt it did, climaxing in the eruption of the Fish Canyon Tuff out of the La Garita caldera some 28 million years ago.

This eruption deposited some 1,200 cubic miles (5,000 cubic kilometers) of ignimbrites across North America in the largest known single eruption in the last half billion years.

The San Juan Volcanic Field in southern Colorado contains up to 18 calderas and as many identified flow deposits and represents the center of this activity.

The La Garita caldera measures some 22 by 47 miles (35 by 75 kilometers) and was active for a couple million years after the Fish Canyon eruption.

Its output was prodigious.


Map of San Juan Volcanic Field from Geological Society of America http://gsabulletin.gsapubs.org/content/120/7-8/771.abstract

Map of San Juan Volcanic Field from Geological Society of America

A related volcanic field in central Colorado buried a stand of redwood trees west of Pike’s Peak near Florissant, Colorado.  The fossilized stumps have been partly excavated and can be seen Florissant Fossil Beds National Monument.  They date from around 35 million years ago.


Fossilized redwood stump – Florissant Fossil Bed National Monument, Colorado.  Buried by volcanic eruption from 39-mile volcanic area, Colorado http://www.conifers.org/cu/Sequoia.php

Fossilized redwood stump – Florissant Fossil Bed National Monument, Colorado. Buried by volcanic eruption from 39-mile volcanic area, Colorado

As the disconnected piece of the Farallon plate melted, it is thought to have provided a source of eruptible material in Nevada, Utah and Northern New Mexico until around some 19 million years ago when the source was depleted.

As large and as active as this area was, it does not formally comprise a Large Igneous Province (LIP).  Interestingly enough, during this time there was a LIP erupting in the Afar – Ethiopia region that was most active around 30 million years ago.


Impact Events.

There are three large craters identified that date at around the 33 million year point when the climate changed.  One formed the mouth of Chesapeake Bay south of Washington DC.  The crater is 53 miles (85 kilometers) across and is thought to be formed by a body a mile or two (3 – 5 kilometers) in diameter.


Map / drawing of Chesapeake Impact Crater – from US Impact Craters http://www.impactcraters.us/chesapeake_bay_virginia

Map / drawing of Chesapeake Impact Crater – from US Impact Craters

A second impact crater has been identified about 200 miles (320 kilometers) northeast of this crater.  It is offshore New Jersey and called Toms Canyon.  It has also been dated around the same time as Chesapeake Bay.  Toms Canyon measures 9 – 12 miles (15 – 20 kilometers) across and was formed by a much smaller body.


The third large impact crater is Popigai in Siberia.  It dates around the same time as Chesapeake and Tom’s Canyon, but was formed by a larger body.  It measures some 62 miles (100 kilometers) across and was thought to be formed by a 3 – 5 mile (5 – 8 kilometer) diameter body.  This crater is little studied as the Soviets found shock-created diamonds at the site and used residents of the Gulag to set up mines for them.


Popigai Impact Crater, Russia (Siberia). From Elite Daily

Popigai Impact Crater, Russia (Siberia). From Elite Daily

There are numerous smaller impact craters measuring in the few miles to kilometers across that date sometime in the Eocene, and it appears that Earth was in the midst of a shower of inbound bodies for several million years.  Eventually the serial insults to the climate built up to the point where natural processes were unable to keep up and the climate changed.


Discussion and Conclusions

Where to go with all of this?  There are several observations to sort out and place into some sort of framework.

The first observation would be that massive volcanic eruptions appear to be insufficient to place the planet into a new Ice Age or by themselves cause an extinction event.  This is not to say that they don’t do enormous damage, kill a lot of plants, animals and people.  But an extinction event means you wipe out all members of a species worldwide.  Some actual study of reported global temperatures for the last century compared with volcanic eruptions by Willis Eschenbach over at “Watts up With That” tend to show less impact than we would think.  I find both the article and the comments significant food for thought.


From Western Geo Hikes – reference map showing all calderas in San Juan Volcanid Field and their dates of origin. http://www.coloradogeohikes.0catch.com/Colorado/SJVF/SJVF.html

From Western Geo Hikes – reference map showing all calderas in San Juan Volcanid Field and their dates of origin.

The second observation would be that massive release of volcanic material into the environment (Large Igneous Province outbreak) does not necessarily lead to a massive global temperature change or extinction event.


A third observation would be that existing volcanic activity needs to be supplemented with some other massive insult to the planet to trigger a long-term change in climate or an extinction event.  And that additional insult, whether impact event(s), close supernovae or other interstellar event, must be sufficiently large so as to push an already stressed system over the edge.

A final observation is that we know that this planet gets hit by impacting bodies at some currently unknown rate.  That flux of bodies is not limited to asteroids whose orbits are (mostly) known.  They also comprise comets and the remains of fragmented comets whose orbits we find out about the first time we see them days to months before they arrive in the inner solar system.  They can be significantly faster than asteroids and are not limited to orbits near the plane of the ecliptic.  And these bodies can be very large.  Comet 1993 Hale Bopp was some 25 miles (40 kilometers) across.  We have yet to characterize either the population or the danger posed by these bodies.  Note finally that the majority of meteor showers take place when the orbit of the earth crosses that of known comets.

My conclusion would be that as large as possible volcanic eruptions may be, even they need help from one to many somethings equally or more powerful to push this planet over the edge into massive climate change or mass extinctions.  All of which makes me a lot more comfortable about ignoring the incessant hectoring from the environmentalist community.  This does not mean we shouldn’t be Good Stewards of our home.  We absolutely should.  But our home is a whole lot more stable and resilient than any of us suspects.

Thanks for reading and I look forward to your comments.


Additional reading:


274 thoughts on “What happened at the end of the Eocene?

  1. todays update up to 16h04

    I have changed the color according to the last 3 days. The 2 quakes @ 9 km depth are clearly visible

    Happy Xmas !

  2. Got word today I will be ready to go back to work in 14 days my PT is doing very well-and I can fly again! Merry Christmas one and all!!!

      • Dunno about that. This will be like #3 to try and get it back into a usable condition. If it fails it could place him in a perm disabled status. As an operator of heavy machinery, you sort of need all your joints working.
        I absolutely hate soap operas, but the way his lawyer is talking, he won’t be able to sue the company for their shoddy maintenance on the unit. Dunno how that works out. Witnesses have noted that the unit effectively had no parking brake even when it was fully engaged. He had parked it and set the brake, had the indicator that it was on before he powered the unit down. Thing took off down the hill with him on top of it. Attempts to restart it in order to at least get steering control failed. He bailed after it went above about 35 mph, headed down hill and off-road. It caught the edge of his foot as it went by…. luckily in semi-soft soil, or it could have been worse. The only smart thing that happened was that they called me first. Had they called his mom she would have been freaking the @#%$ out. I at least had a grasp on his condition before I told her.

  3. Happy Holidays to everyone. Congrats on the kudos, Carl. I have less than six hours to go til midnight. I will probably be asleep and miss The Jolly One. (Santa) Also, thanks to all the authors and commenters for all the hard work it takes to make this such a first-rate quality site.

  4. It is starting to look like the tremor is constant now… this is the second period of constant tremoring. I think we are close to an eruption. Hours or days.
    Still following exactly the same pattern as the last time.

  5. And Lurkings favourite frequency at 0.26Hz is up and running like insane. CHIE does not show it due to technical reasons, but CFUE, EGOM and EFAM is really showing it.
    I wonder if one could track the exact location of the mantleplume-head by comparing this 3 if one had access to all 3-axises of these 3 stations.
    For the rest, this is ultra-low tremor that is to low in frequency to be withing a system, me and Lurking stipulated that it might be plume movement or extremely deep magma movement. Something that has gotten increasingly likely due to it occuring only around volcanic activity.
    It is not movement of magma in a conduit, that would require a conduit 500 meters wide, anything tighter would filter out this extreme low frequency.

    • I just came home from a nice early chritsmas dinner with my beloved family and i must say i’m pretty toxicated:) And i probaly should’nt be posting here. But you mention CFUE, EGOM and EFAM. That’s Fuerta vetura, La Gomera and Landzarote. If you ad El Hierro that’s about the whole Canarie island chain. That implies alot!

      • I’m not sure if i understand you. Do you mean the peak in the spectral analysis as show here:
        Lanzarote, or:
        Do you really think this could actually be coming from the mantleplume? I Can’t see data back for more then a year, but the peak always seems to be there. Ctig shows it to, Ccum alot less.
        Some times there are a few other low frequencies peaks aswell also showing on most stations, like a year ago.:
        Same double humb is visible on fuertaventura and la gomera that day. Other days there are 3 humbs also visible at those 3 stations. No coincidence i’d say.
        I find this pretty amazing. I always considered it back ground noise,waves, weather or some instrument artifact. But it sure looks likes it could be something real!

        • “Do you mean the peak in the spectral analysis”

          Yes. The physics for that to show up require a relatively huge resonant chamber. The idea is that it is material oozing around very deep. Likely feeding into the system.

          A short recap of El Hierro.

          At one time, this area was in a pull-apart basin as the Atlantic began to open up. Sediment accumulated in this basin and over time, was buried by even more sediment. The sediment de-watered, and became compressed into mudstone, then eventually, shale. At some point in time, magma pushed up through the buried oceanic crust and the sediment layers on top and formed the island. With the added load of marine sediment, and the volcanic debris, the original sediments of the basin began to metamorph into phylitte. I don’t think that there is enough pressure to take it all the way to schist.

          Where this is important is in the formation of the Restolingas. (Bob’s Floaters). Analysis of them has shown a quite high silica content, high enough to be chracterized as Rhyolite by some labs, others argue for Trachyte. I think the high silica portion come from mobilization of the Jurassic era sediment material as the magma pushed through. Essentially, melted Xenolith.

          Back when Bob initially formed, the quakes tracked south and deeper as the magma dove underneath the “keel” of the island and popped out near the El Julan slide area. To me, it seemed to follow the weak area on the scarp face, but my eyes may have just been playing tricks on me in the plotting. The collection of quakes preceeding the actual vent formation were not noted in the list until after the jacuzzi was up and running. Probably too poorly located to list until after further analysis.

          The one thing that has always kept the hair on the back of my neck on end… is that the island is laced with old pipes and magma tubes. They form the caves that are prevalent throughout the area. The entire island is covered with old scoria cones, all it would take is for a finger of magma to find one of those old tubes and you have an instant path to the surface. Personally, I would rule out spelunking right now. Unless it was to place a gas sensor at the entranceway and then leave to find a beer.

          • Brilliant recap!
            You should really write that up with a couple of your plots so that the newcomers get to know and love El Hierro and Bobolito as we oldtimers do. 🙂

            • Thanks for an excellent answer Geo! It’s not the right evening for making long replies. I reply tomorrow. This could say something about the whole plumbing system of the chain.

            • “Far enough away” Probably a very important requisite. The last thing I would want is to be down in one of those caves and have it become the new found path. Even though basalt is the predominant driving mechanism, no one knows how the mobilized high silica material will take on gases, and then release them when the pressure drops low enough. Could be quite energetic if done in the right way. I imagine that prior to that, the toxic gas levels in the tube(s) would become quite lethal.

              Rumination. Aided by my Christmas present. First time anyone got me a bottle of whiskey for Christmas. It’s a brand I’ve never tried, but it is corn whiskey, nicely aged apparently. (Tastes like it). Sipping a shot now and chasing it with grapefruit juice.

              As the default IT guy in the family, I had to set-up Skype so that the USArmy grandkid could be part of the dinner get together. The big announcement that he was holding off on is that his wife is pregnant. Technically, that would make me a great grandfather. The outstandingly cool bit is that makes his mom a grandmother. That pisses her off to no end. She still considers herself quite the number, an issue which led to a divorce from my step-son. Being a grandparent sort of takes that “hotness” attitude and tosses it aside, no matter how well you think of yourself you are not going to escape it. ‘You are a grandparent, deal with it!’

              Wanna know a secret? We grandparents take quite a bit of delight in loading the grandkid up on sweets before we sent them home. Talk about a ball of pure energy….

  6. I wish every volcanophile in here a very happy Christmas season and power to your stomachs to digest all the turkeys, geese, ducks, pigs, cattle, cakes, puddings, chocies, cookies, bisuits, nuts, candies, oranges, apples, spicies, asf.; a happy and healthy year 2014 to all, and also a good new year to our Volcano Cafe. May it and the volcanoes prosper!

    • I must say that the colour of the Gravatar goes well with your newish name :mrgreen:
      I am almost imobilized today from all the food. I had really planned to write a post on El Hierro, but thankfully I can wait untill tomorrow with that one…

  7. Merry Christmas to everyone. I’ve been helping my daughter who is recovering from back surgery and lurking as much as possible. Very excited about “Zombie Bob”!

  8. Here I m learning how to use my new KIndle fire. Hope you are all feeling. A warm Cristmas glow. Off to practice hunting for volcanoes on this little android. Husband says he is already a KIndle widower.

    • I agree, it is looking exactly like it did the last time before it went into overload.
      If it continues like the last time the tremor will increase continuously untill it suddenly breaks through and we get an overload of the sensor.
      Question is perhaps more when, than if…

  9. Hope everyone had a wonderful day today as I did also despite doubts yesterday as my son FINALLY got home to South of England from Wales yesterday after trying since the afternoon of the 23rd Dec. No trains running south of London or from the west yesterday, thought he may have to walk it in the end! As it was he got withing 65 miles from here and my kids had to drive and collect him of he would have been stranded on Christmas eve! That was one almighty storm down here and way too much rain. Wish it had been snow and wishing lots of snow to all my friends and enemies alike. 😉 ROFL.
    And what on earth is happening at Tenerife???? http://www.ign.es/ign/head/volcaSenalesDiasAnterioresCuasiReal.do?nombreFichero=CCAN_2013-12-25&ver=s&estacion=CCAN&Anio=2013&Mes=12&Dia=25&tipo=1
    Is it broken?

    • They were saying on AVCAN’s FB page yesterday that CCAN was malfunctioning.

      Hope your son is not planning to travel on Thursday evening / Friday – another storm is forecast 😦 Stay safe.

  10. Is what is happening at El Hierro a repeat of what happened in March or will this end in an eruption this time around?

  11. Everybody has their pet theory of how things work. Some are their own, some are adopted from others. My Antipodal hotspot idea is not mine. There is a paper over at mantleplumes that details the idea. Its just that to me, the idead of converging shockwaves that trigger or enhance geologic activity seems quite elegant, and usually, the simpler ideas are pretty close to reality.

  12. Pingback: Paricutin, Mexico – My First Volcano | Volcano Hotspot

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