The Age of Supereruptions: Climate Effects

Note:  This is a volcano post, but we need to mention a few other interesting things first.  And everything is better with a cat in it.

Human beings didn’t invent climate change; it’s built into the plane.

We’re actually survivors of some of the most dramatic natural changes ever: the ice ages.

Earth started having glacial/interglacial cycles 2.6 million years ago, right around the time that our ancestors first realized that stones can be made into useful tools.  (Agustí and Antón; Coolidge and Wynn)

Since then, people have seen at least 20 ice ages come and go.  For the last million years, the 100,000-year cycle has been quite regular. (Petit and others; Smithsonian)

Our progress through ice ages and the intervening warm interglacial periods—like the one we’re in now—can be measured by the number of controlled barriers we have erected between us and the unpredictability of the great outdoors.

Not all the barriers have been successful.

It’s a rough world out there.  And even though volcanoes are the ultimate source of our atmosphere (Schmidt and Robock), they’re out to get us, too.

The deadliest eruption in history—at Indonesia’s Tambora in 1815—may have directly and indirectly killed over 100,000 people.  (Oppenheimer, 2011)

The second most extreme supereruption known (Mason and others; Self) happened at another Indonesian volcano called Toba roughly 73,000 years ago, during the middle Stone Age.  (Oppenheimer, 2011)  It may have almost  wiped out the human race by triggering a “volcanic winter.”  (Self)

Nonetheless, despite such formidable natural hassles, the definitive history of humanity, whenever it gets written, may ultimately reveal that we were our own worst enemies.

By the year 2400, humans will have added an estimated 5,000 gigatonnes of carbon to the environment since the industrial age began.  (Zachos and others, 2008)

No one knows if the planet can absorb that much greenhouse material and still stay cold enough to maintain polar ice caps and to have glacial/interglacial cycles.

The ice-age climate that obviously suits us the best, since we evolved in it, is not the planet’s baseline.  (Hay)  In fact, what we call “normal” is really just a small part of Earth’s climate spectrum.  (Lyle and others, 2008

So what will happen to us ice-age relicts, if and when manmade global warming shuts down the ice machine?

To get some idea of what we can expect next, researchers are combing through the rocky, muddy geologic record for clues on how the planet and its life responded to high CO2 levels in the past.  (Lyle and others, 2008; Zachos and others, 2008

The Paleocene/Eocence thermal maximum

Everybody interested in climate ends up talking about CO2 sooner or later.  This greenhouse gas is plentiful and it regulates climate on time scales ranging from a year to millions of years.  (Royer and others

But geoscientists must go back 55 to 56 million years to find natural greenhouse gas loading anywhere near the magnitude of what humans are pouring into the environment today.

Around the boundary time between the Paleocene and Eocene epochs, some 10 million years after the K/T mass extinction, land and sea temperatures suddenly soared, and an estimated 2,000 gigatonnes of carbon entered Earth’s oceans and air.  (Jardine)

That thermal maximum took 6,000 years to reach its peak—roughly ten times as long as our man-made thermal max will take.  Then global temperatures and CO2 levels dropped back down to baseline over the next 150,000 to 200,000 years.  (Jardine)

Surprisingly, this Paleocene/Eocene Thermal Maximum (PETM) wasn’t lethal to most life on Earth.  The only recognized mass extinctions from it involved deep sea creatures.  (Prothero, 2004)

But there were significant changes in mammal evolution around then.  (Figueirido and others)  Some archaic forms went extinct, and at least three modern groups made their first appearance  (Jardine), possibly in Asia (Beard):

  • Our own group – the primates.
  • Odd-toed hoofed ancestors of today’s horses, rhinos, tapirs, etc.
  • Even-toed hoofed ancestors of camels, deer, cows, etc. 

Some of these hoofers, along with other Asian animals, eventually migrated into North America late in the Eocene to join the White River Chronofauna that was taking shape there on the central plains.  (Mullin and Fluegeman)

We’ve met the White River Chronofauna in previous posts.  It was one of the most stable collections of prehistoric animals ever, despite its location next to an ongoing volcanic apocalypse known as the Great Ignimbrite Flareup.

In addition to supervolcanism, these animals also faced a crisis that some experts call “the most significant episode of climatic change and extinction since the end of the Cretaceous, with the exception of the Paleocene/Eocene boundary event.”  (Berggren and Prothero)

Berggren and Prothero are not exaggerating.

As the White River Chronofauna came to dominance in North America, the chemistry of Earth’s atmosphere shifted dramatically and the entire planet switched over its climate from “hot and muggy” to “cold and dry.”

From greenhouse to icehouse

Geological records show that Earth’s climate has at least two different but stable “settings”:  a high-CO2  “greenhouse” and today’s low-CO2  “icehouse.”  (Lyle and others, 2008)

The Eocene started out as a greenhouse, like the Paleocene epoch before it and, for that matter, like the closing years of the Age of Dinosaurs.

Whatever caused the end-Cretaceous major mass extinction 65.5 Ma (million years ago) destroyed ecosystems around the world (McGhee and others), but it didn’t shift global climate away from its “greenhouse” setting. (Agustí and Antón)

Not even though the sky itself may have been aflame.  (Robertson and others)

The PETM, 10 million years later, was the first big climate test of the Age of Mammals.

As mentioned above, Earth passed that test with flying colors.  Runaway global warming didn’t happen when roughly 2,000 gigatonnes of carbon hit the environment.

Instead, feedbacks—at least some of them related to the planet’s carbon cycle—brought temperatures and atmospheric CO2 levels back down to  baseline . . . the greenhouse baseline, which had carbon dioxide levels that were several times higher than today’s. (Lyle and others, 2008; see Bains and others)

If you’re now wondering how a high-CO2 world could cool down after such a big carbon surge  . . . well, so are the scientists. (Lyle and others, 2008)

Anyway, things returned to baseline and the planet had a nice greenhouse optimum for a couple million years. (Zachos and others, 2001)  Then something very unusual happened.

Earth’s climate broke down.

It started out slowly, but the last and most dramatic event happened very quickly in geologic terms:

  • 51 Ma:  In the early Eocene, long-term high-latitude cooling began.  (Tripati and others)  Temperatures did return to baseline afterwards.  There were also some hyperthermals (Bohaty and others), not as intense as the PETM, and feedbacks cooled the world back down after each one.  More cold spells, lasting 1-2 million years each, came at around 48, 45, and 42 Ma.  (Lyle and others, 2005; Tripati and others)  
  • 47 Ma:  Mean temperatures near the Equator weren’t affected over the long term by cooling (Sage), but winters there became a little colder and less rain fell during summer.  (Agustí)  Since a closed-canopy forest needs a mean annual rainfall of some 60 inches ( 1,500 mm), tropical rainforests at lower latitudes began to open up. (Edwards and Smith)
  • 42 Ma:  The middle Eocene cooling at 42 Ma was the biggest chill of the epoch thus far, with major tropical sea cooling.  (Lyle and others, 2008)  Temporary mountain glaciers began to form in Antarctica (Francis and others)  and ice may have also appeared in the Arctic Ocean.  (Tripati and others)  This episode lasted until around 40 Ma, when the planet warmed back up unusually quickly (Lyle and others, 2008), only to cool down gradually, with just a few small temperature swings, over the rest of the Eocene.  (Tripati and others
  • 40 to 37 Ma:  In the late middle Eocene, some groups of, first, tropical and then warm-water marine creatures went extinct.  Many archaic forest-dwelling animals also disappeared (Prothero, 1994), but North American mammals otherwise were unaffected by the climate changes. (Prothero, 2004)
  • 37 Ma:  Greenland got frosty during the late Eocene, but warm summers there probably limited ice cover to mountain glaciers.  (Eldrett and others)  The drying out of Earth’s water cycle continued.  In North America, forests requiring 3.3 feet (1 meter) of annual rainfall were replaced by less dense forests that could get by on half that much precipitation.  (Prothero, 2004)  
  • 33.7 Ma:  The big freeze.    Climate changes accelerated.  Over a mere 300,000 years, permanent ice sheets expanded over eastern Antarctica and the carbon storage space in the ocean increased dramatically.  (Lyle and others, 2008; Zachos and others, 2001)  In North America, mean annual temperatures plummeted and rainfall became much more seasonal.  In less than 500,000 years, the paratropical rainforest that had covered central North America during the greenhouse was replaced with a broadleaved deciduous forest similar to the one seen today in New England and eastern Canada.  (Prothero, 2004)  And while it’s not known for sure, evidence suggests that, as the world became even cooler and drier, this forest quickly turned into the wooded savanna (Strömbergthat the White River Chronofauna would call home for many millions of years. 

Since then, Earth has had some warm spells, but the greenhouse has not yet returned.  Instead, global climate overall has gotten cooler and drier (Lyle and others, 2008; Zachos and others, 2001), and here we are today with both poles in the deep freeze and cycling ice ages.

Perhaps another greenhouse is on the way, all because some primates have become players in the global climate game by inventing an industrial age.

If that’s so, it doesn’t seem likely that we’ll get help from whatever climate feedbacks cooled the world back down to baseline after the last major greenhouse load – the PETM.

Antarctica’s ice cap is evidence of their spectacular failure.

Mountains at Paradise Bay, Antarctica, are certainly spectacular.

Volcanoes and climate

There is an urgency to climate research today

Processes involved in Earth’s complex carbon cycle usually take millions of years. (Kump)  But as we just saw, in only 300,000 years (not much more than a few seconds of geological time):

  • Permanent ice sheets, with almost half the mass of today’s ice cap (Zachos and others, 2001), appeared on Antarctica after many millions of years of warm temperatures there.  (Smithsonian)
  • Carbon storage area in the world’s largest ocean basin—the Pacific—jumped from 20% to 45% of Earth’s surface.  (Lyle and others, 2008

This suddenness shows that major changes in climate can be set off very quickly under the right circumstances.  (Lyle and others, 2008; Zachos and others, 2001)

The big questions are what the climate triggers are and what circumstances set them off.

To find out, researchers are feeding data from the geological record into supercomputers and investigating past as well as future climate conditions with various models.

Some computer studies of glacial/interglacial transitions during the ice ages show that climate feedbacks related to water vapor, sea ice, and perhaps also clouds operate differently when modern carbon dioxide levels are doubled.  (Petit and others)

Too, modeling of Earth’s climate 80 million years ago, when CO2 levels were many times higher than they are today (Lyle and others; Pagani and others), suggests that positive feedbacks between water vapor and CO2 kept the planet’s poles warm enough to support forests and temperature-sensitive animals like crocodiles and flying lemurs. (Smithsonian)  These feedbacks would have worked at any latitude (Hay), though nothing like this exists in today low-CO2 world.

Modeling is useful, but it’s also very difficult because Earth’s climate is more complex than anyone expected.

Climate basics themselves aren’t hard.  For instance,

  • Weather is what air, wind, and atmospheric moisture are doing outside your window at any given moment.  Climate is the same thing averaged over time.  (Strahler, UCAR)  
  • Global climate is driven by solar energy and by the amount of energy that gets trapped in the system.  (UCAR)
  • Greenhouse gases are our friends.  The Earth is a pleasant blue marble, not a radiation-blasted waste like the Moon, because greenhouse gases—mainly CO2  and water vapor—hold some solar energy at the planet’s surface while  allowing the rest to radiate back into space. (Strahler)
  • Our planet’s energy budget is always balanced.  (Strahler)   This means that if you keep adding heat-trapping greenhouse gases, something’s got to give, sooner or later.
Earthrise as the Apollo 8 astronauts saw it. (NASA)

It’s the climate system that’s complicated, in ways that go far beyond the scope of a simple blog post. (See, for example, Brown and others; Falkowski and others; Lyle and others, 2008, sections 2 through 6; Rea and Lyle, section 5.3; Redfield; Rial; and Woodard.)

Researchers get useful insight into this complex system by studying how it responds to volcanic eruptions.  (Robock, 2000)

The primary effect an eruption has upon climate is well understood, thanks to satellites and ground-based remote sensing studies over the past five decades.  (Oppenheimer, 2011)

Sulfur is the culprit, even though carbon dioxide is a more common volcanic gas (and climate scientists must subtract the volcanic contribution before they can measure man-made CO2 emissions).  (Mather and Pyle; Robock, 2000; Schmidt and Robock)

Let’s suppose there is a big explosive eruption somewhere. When the eruption cloud reaches the stratosphere, which is about 5 to 11 miles (9 to 17 km) above the ground, depending on the volcano’s location (Peate and Elkins-Tanton), chemical and physical reactions turn sulfur gas (SO2) into tiny particles of sulfuric acid.  This cloud of aerosolized sulfur interacts with incoming sunlight in complicated ways. Most importantly for global climate, it changes Earth’s heat budget by backscattering incoming short-wave radiation so that less of the Sun’s heat energy reaches the ground.  (Egger and Brückl; Oppenheimer, 2011; Robock, 2000)

Regional effects vary, but the overall effect of this scattering is surface cooling.

Very generally, according to Self, cooling is:

  • Global, if the volcano is within 15 degrees of latitude from the Equator.
  • Both hemispheres, but mostly in the volcano’s hemisphere for an eruption  located 15 to 30 degrees north or south of the Equator.
  • One hemisphere, if a volcano between 30 and 90 degrees north or south erupts.

Not all volcanoes have enough sulfur in their magma to cause major climate disturbances, but the eruption of Mount Pinatubo near the Equator in 1991 put enough sulfur up there to affect Earth’s heat budget for more than three years, until all of the sulfate aerosol fell out of the sky.  (Self)

Top:  Fairly clear stratosphere imaged by Space Shuttle astronauts in August 1984. The dark towers are the tops of thunderstorms.  Bottom:  Less than two months after Pinatubo’s 1991 eruption, there are two dark layers of aerosols in the stratosphere. (NASA)

For the first two years, Pinatubo’s cooling effect offset man-made global warming! (Oppenheimer, 2011)

However, two or three years isn’t much time on a 4-1/2-billion-year-old planet.

There is no evidence yet that a big eruption can affect climate over geologic time spans.  (Mather and Pyle)

That includes supereruptions like Yellowstone’s Huckleberry Ridge blast, as well as somewhat less powerful VEI 7 eruptions like the one that formed Oregon’s Crater Lake less than 8,000 years ago.  These are very destructive, but they are also few and far between.  (Mason and others; Mather and Pyle)

Tens of thousands to millions of years can pass between such big eruptions.  (Mather and Pyle; Miller and Wark)  This means that the planet has plenty of time to recover from each catastrophic event. (Self and others)

But what about eruptions that happen over and over again, maybe wearing down the climate system over time?

Eruptions like the Great Ignimbrite Flareup?

Eocene supereruptions

The Great Ignimbrite Flareup was quite an event. Just the fact that it involved ignimbrite is impressive.

We’re used to the sort of ashfall and pyroclastic flows that have happened during historic explosive eruptions.  These are awful, as residents of Pompeii found out in 79 AD., but ignimbrites take it to an even more extreme level.

Ignimbrites are also pyroclastic flows (Miller and Wark), but they can be big enough to bury entire landscapes under a new plateau.  (Wilson)

Cascada de Basaseachic, Sierra Madre Oriental.  All that rock is just one
ignimbrite flow, after about 28 million years of weathering.  (Miller and Wark)

The Great Ignimbrite Flareup happened, back in the Eocene and Oligocene, because of a complex tectonic situation along the coast of western North America and northern Mexico. (Chapin and others; Ferrari and others)

As part of the flareup, three 20,000- to 50,000-cubic-kilometer bursts of ignimbrite built the Sierra Madre Occidental range in Mexico. (Oppenheimer, 2011)

Volcanism on a scale like that goes beyond supereruptions to something called a large igneous province (LIP). (Bryan and Ferrari; White and others)

The Sierra Madre Occidental LIP was contiguous with intense volcanism in the southwestern US and Great Basin regions  (Bryan and Ferrari), where  at least 86 regional ignimbrites were emplaced from Trans-Pecos Texas to Colorado.  The total ash volume here was at least 30,000 cubic kilometers.  (Chapin and others)

And that’s not all there was to the great flareup.

Tens of thousands of cubic kilometers of ignimbrite from over 200 explosive eruptions, at least 30 of them supereruptions, also surged over parts of Utah and Nevada at this time.  (Best and others)

Some of the Utah and Nevada ash reached the home of the White River Chronofauna, on the northern Great Plains.  (Larson and Evanoff)

Three of Earth’s largest known eruptions—Barrel Springs and Wild Cherry in Texas and the Oak Creek Tuff in New Mexico. (Mason and others—happened in the Eocene during the Great Ignimbrite Flareup.

And wait, there’s more! Eocene volcanism elsewhere in the world included, but wasn’t limited to:

  • 75 to 45 Ma, western North America. Pre-flareup explosive volcanoes erupted from northwestern Arizona, northern New Mexico, and Colorado to Guadalajara. (Chapin and others; Ward)  
  • 70 to 48 Ma, North Atlantic.  The opening of the northern Atlantic Ocean led to the eruption of millions of cubic kilometers of basalt. (Keep this one in mind; we’ll mention it again in the next section.)
  • 50 to 44 Ma, Pacific Rim. Reorganization of the Pacific tectonic plate (Ward) led to subduction and associated explosive volcanism in the Aleutians, the Izu-Bonin-Mariana arc, and the Tonga-Kermadec arc.  At the same time intense volcanism happened along the Challis-Kamloops belt from Wyoming to the Yukon.  (Jicha and others)  This included another of the world’s largest known eruptions: the Challis Creek supereruption at Twin Peaks caldera in Idaho, 45 Ma. (Mason and others)
  • 50-16 Ma, Great Ignimbrite Flareup.  The timing of the Sierra Madre Occidental eruptions isn’t well understood yet.  (Murray and others)  In the Texas/New Mexico/Colorado portion, there were three pulses of activity:  37.5 to 31.4 Ma, then 29.3 to 26.8 Ma, and finally 25.1 to 23.3 Ma. (Chapin and others)  Ignimbrites flowed over parts of Utah and Nevada from 36 to 18 Ma.  (Best and others)
  • 45 Ma to 27.7 Ma, Africa and Arabia:  LIP eruptions happened in the northern Ethiopia and Yemen volcanic province and the East African triple junction. LINK Ethiopian flood basalts erupted starting around 45 Ma.  (Hofmann and others)  The most intense phase of this LIP eruption, however, happened in the Oligocene  (Hofmann and others; Jicha and others), after the icehouse climate change was underway.  The Afro-Arabian silicic large igneous province and flood volcanism also erupted during the Oligocene. (Peate and others, 2005)  The East African Rift is thought to have been active in pulses, including during the middle to late Eocene (44 to 38 Ma).  (Peate and others, 2003)  Volcanism in the other two triple-junction arms isn’t well dated. (Buck

By the way, just for reference, the Eocene is the longest epoch of the Age of Mammals. It lasted from 55.8 to 33.9 Ma. Our own epoch—the Holocene—is only 11,700 years old.

All told, researchers say, 500 large eruptions happened in western North America and around the Pacific between 35 and 28 Ma, or one about every 13,000 years.  (Jicha and others)

No wonder the Eocene climate broke down!

That may be easy to say, but clearly established links between Eocene volcanism and the Eocene/Oligocene climate transition are very elusive.

After all, those nearby supereruptions and ash flows in North America didn’t faze the White River Chronofauna at all.

The White River animals had other priorities.

Experts have thus far identified  only one possible eruption/climate change “smoking gun” back then.

And its effect on climate was just the opposite of global cooling.

Linking Eocene volcanism and climate change

We have to go back to the opening of the North Atlantic to find a possible link between volcanoes and climate.

When the Age of Mammals began, 65.5 Ma, North America and Europe were connected via a land bridge through Ellesmere Island, Greenland, and land that is now under the North Sea.  (Smithsonian)

However, tectonic forces had been slowly stretching out that area for hundreds of millions of years.  (Meyer and others)

When the break finally developed between Greenland and the Faeroe Islands, around 62 Ma, it kicked off  a complex event that would ultimately involve the eruption of anywhere from 1 to 10 million cubic kilometers of basalt lava.  (White and others; See discussions in Meyer and others; Mjelde and others; and Storey and others)

Beautiful, beautiful basalt lava.  Fingal’s Cave (left), which has inspired classical music, and the Giant’s Causeway (right) are part of the North Atlantic igneous province.

The episode we’re interested in was just a tiny part of all that, but if it happened the way some experts suspect, it had very big consequences.

Around 56 to 55 Ma, according to some geoscientists, underground sills of molten magma broke into organic-rich sedimentary rock at the bottom of what is now the Norwegian Sea.  This released gigatonnes of methane that bubbled up through the water and escaped into the atmosphere.  The methane quickly turned into CO2, and greenhouse gas levels soared.  (Svensen and others; also see discussion in Dickens; Sobolev and others, Section 10.3; Storey and others)

If this scenario is correct, North Atlantic volcanism set off the Paleocene-Eocene Thermal Maximum (PETM)!

But that hasn’t been definitely established yet, and some nonvolcanic causes for the PETM are just as plausible. (See review in Sluijis, Chapter 5, pp.84-87.)

Other than that one possible volcanism/climate change link, there are only hypotheses that need more data to gain wide acceptance.

For example, roughly 26,000 years passed between major eruptions in the North Atlantic.  That’s plenty long enough for climate recovery.  However, some experts suggest that the climate effects from each big eruption could have been extended to almost 600,000 years by additional aerosols and dust from many smaller ongoing eruptions that obviously happened, given the volume of North Atlantic basalt, though each small eruption left no distinctive mark in the geological record. (Egger and Brückl)

Another approach to the problem focuses not on aerosols and cooling, but on carbon dioxide.

CO2 and iron fertilization

Carbon dioxide levels did fall dramatically as our planet went from the greenhouse to the icehouse.

The exact details are still under debate (Tripati and others), but according to one widely accepted version (Pagani and others):

On a broad scale, our results indicate that CO2  concentrations during the middle to late Eocene ranged between 1000 and 1500 parts per million by volume . . . and then rapidly decreased during the Oligocene, reaching modern levels by the latest Oligocene . . . In detail, a trend toward lower CO2 concentrations is evident from the middle to late Eocene, reaching levels by the E/O boundary that could have triggered the rapid expansion of ice on east Antarctica . . .

Since atmospheric carbon dioxide levels are regulated, in part, by volcanic outgassing (Mather and Pyle), maybe Eocene eruption flareups and LIPs played a role in that dramatic fall in CO2.

The only problem with this idea, besides lack of any clear-cut evidence, is that volcanoes emit lots of CO2.  If anything, the fiery flareups of the Eocene should have increased the amount of carbon dioxide in the air.

A hypothesis that links volcanism to the Eocene/Oligocene drop in CO2 uses myriads of very small marine creatures to explain the big picture.

Phytoplankton like these diatoms are tiny plant-like creatures that live in the upper levels of the sea, where sunlight penetrates to some depth.

Their photosynthesis is an important link in the cycles that move important elements like nitrogen, carbon, and oxygen back and forth between the ocean and the air.  (Browning and others; Redfield)

According to Falkowski and others, phytoplankton sequester 11 to 16 gigatonnes of carbon every year!

As these billions and billions of little critters do photosynthesis, they take carbon out of the surrounding water.  This makes the partial pressure of CO2 in the upper ocean go down, forcing the ocean to absorb more carbon dioxide from the air.  About a quarter of all carbon fixed in the ocean this way sinks and is stored at depth as inorganic carbon.  (Falkowski and others)

Phytoplankton thrive near the continents or in areas where deep waters well up to the ocean surface.  These regions have all the necessary nutrients.  Out in the vast open ocean, there isn’t much iron available to make chlorophyll.  As a result, phytoplankton activity out there is very low, just a few little floaters living on whatever iron-bearing dust the wind happens to carry out to sea.  (Cather and others)

Sometimes the wind brings volcanic ash, too. That’s a bonanza, because each volcanic particle often carries a coating of iron that dissolves quickly in the water.

That iron leads to a surge in photosynthesis, perhaps enough to significantly lower atmospheric CO2 levels.  (Browning and others; Cather and others; see review by Duggen and others.)

Two of the four largest eruptions since 1958 were indeed followed by temporary drops in atmospheric carbon dioxide.  (Cather and others)

And satellites have identified phytoplankton blooms after a couple of recent eruptions.  Unfortunately, little is known about them.  It’s difficult to see these features from space, and no ships were on the scene to collect the necessary data.   (Browning and others)

As for the Eocene/Oligocene transition, it can be shown on paper that the eruption of the Sierra Madre Occidental could have provided over twice the amount of iron fertilization necessary to cause the CO2 drop back then.  (Oppenheimer, 2011

But the location of low-chlorophyll zones in the ancient oceans isn’t known yet (Cather and others), although biomarkers have been found in deep sea drilling cores from near the end of the PETM that may be evidence of increased marine productivity and carbon storage.  (Bains and others

Clearly much more research into iron fertilization and its effects on the carbon cycle is needed. (Browning and others)

Climate effects of LIPs

Perhaps the large igneous provinces of the Eocene and Oligocene had an effect because of their sheer scale and prolonged eruptions.  (Mather and Pyle)

There are two main types of magma, and both erupted in Eocene/Oligocene LIPs:

  • Basalt (dark-colored).  Ordinary basalt eruptions produce the pretty Hawaiian-style lava that runs out over long distances.  Basalt LIPs contain extraordinarily thick layers of this type of lava. However, basalt eruptions can also be explosive, especially when water is involved. (Peate and Elkins-Tanton) One of the biggest basalt blasts recognized in the geological record happened in the Eocene, around 54 Ma, when water met lava in the North Atlantic igneous province.  (Egger and Brückl)
  • Silicic (light-colored). Ordinary silicic eruptions are the explosive kind, with pyroclastic flows and features like lava domes.  SLIPs (silicic large igneous provinces) like the Sierra Madre Occidental are built out of ignimbrites and are the biggest explosive eruptions on Earth.  (Bryan and others)

Basalt magmas have more sulfur than silicic magmas. (Self and others)

This means basalt could have more of a climate effect, but only if the eruption columns reach the stratosphere. They usually don’t. (Kaminski and others)

However, even below the stratosphere, volcanic gases may still affect climate by causing more cloud formation.  (Schmidt and others)

The basalt supereruption in 54 Ma scattered ash from Ireland to the Austrian Alps. (Egger and Brückl) It certainly reached the stratosphere.

While more sulfur doesn’t always mean bigger climate effects (Oppenheimer, 2011), the stratospheric sulfate aerosol cloud this eruption spawned must have been much bigger than Pinatubo’s in 1991.

And there is evidence of cooling in the northeast Atlantic region at around the same time.  Sea surface temperatures went down a bit (Egger and Brückl) and northeast Atlantic margin forests experienced cooler, drier climates.  (Jolley and Widdowson)

But this climate change didn’t last.  Despite the supereruption and ongoing flood volcanism in the North Atlantic, as well as eruptions in North America and northern Mexico, Earth’s climate warmed back up into that greenhouse optimum from 52 to 50 Ma. (Zachos and others, 2001)

As for SLIPs (silicic LIPs), their environmental effects are difficult to study for a couple reasons:

  • While these explosive eruptions certainly get sulfur up into the stratosphere, no one is sure exactly how much sulfur the magma originally contained. (Bryan, 2007)  This makes it impossible estimate possible climate changes.
  • In order to to model environmental effects of an ignimbrite eruption, scientists need a reasonable estimate of the eruption size.  That’s not easy, because such gigantic eruptions generate huge ash flows that can deposit ash more than 600 miles (over 1,000 km) from the vent.  After 30 to 50 million years, it’s often difficult to accurately measure the size of the original flow, especially if some of the ash fell into the ocean.  (Bryan and others)

Despite all the challenges, scientists continue to research LIPs because it is quite likely that this kind of volcanism can affect Earth’s atmosphere on a scale of thousands to hundreds of thousands of years.  (Mather and Pyle)

Wrapping it up

We’ve learned more about climate and about all those supereruptions back in the Eocene and Oligocene, but it appears that there is no answer in the geologic record to our man-made climate change dilemma.

That is, no answer just yet.  There are very many clues.

In the Pacific Ocean alone, researchers have almost 65 million years’ worth of sedimentary records that show the “physical, chemical, and biological processes that either caused or responded to the climate changes at Earth’s surface.” (Lyle and others, 2008)

A variety of data is also coming in from all the other oceans and from many other sources, including satellite and ground-based studies of volcanoes and their eruptions.

Montserrat Volcano Observatory in the Caribbean.

Huge databases have been compiled and computer climate models are becoming very sophisticated.

The chances are good that we will soon understand enough about Earth’s climate system to predict at least some of the most vital changes that can happen in a world with higher CO2.

Maybe we’ll also be able to do whatever is needed in time to give our descendants a good world to live in, with or without ice ages.

Of course, we haven’t mentioned something else from the Eocene/Oligocene that is very important.

It is the surprising resilience of life in the face of severe challenges like the ignimbrite flareup and the Eocene/Oligocene climate transition.

The fossil beds where the White River animals now sleep are very extensive and cover millions of years.  If anything had a negative impact on those animals, it would show up here. (Prothero, 2004)

And it doesn’t.  There is no change in this chronofauna even through “the most dramatic climatic change of the entire [last 65 million years].”  (Prothero, 2004)

No one knows how they did it, but life found a way.

And so will we.

IMAGE LIST (not linked in text).  In order of appearance:

FRONT PAGE IMAGE:  Cat Eye Sky (left) by Jay Erickson (CC BY 2.0).  Bardarbunga Volcano, September 4, 2014 (right) by Peter Hartree (CC BY SA 2.0)


  1.  Gojira. Dir. Ishirô Honda.  Toho Company, 1954.  Film.
  2.  Mountains at Paradise Bay, Antarctica.  Image by Jan Borgstede.  (CC BY-SA 2.0)
  3.  Dinictis and Protoceras.  Image by Charles R. Knight, 1904. Public domain.
  4.  North Atlantic igneous formations.  Left:  Fingal’s Cave, Staffa, by Rosa Menkman. (CC BY 2.0)  Right:  Giant’s Causeway, by Jennifer Boyer. (CC BY 2.0)
  5.  Phytoplankton.  Professor Gordon T. Taylor, Stony Brook University, corp 2365, NOAA Corps Collection. .  Public Domain.
  6.  Montserrat Volcano Observatory.  Image by David Stanley.  (CC-BY-2.0).


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