How Flood Basalt Eruptions Cause Mass Extinction

When I was growing up in the 1990’s, it was recently discovered that a giant impact event could have spelled the end of the dinosaurs with the discovery of the Chicxulub impact crater off the Yucutan peninsula in Mexico.  From what I learned back then, this was pretty close to a done deal as the major cause of the death of dinosaurs.

While the Chicxulub impact event was no doubt a dramatic and earth-changing event, it may have overshadowed a similarly destructive event that occurred around the same time – the Deccan Traps flood basalt province. Unlike the impact event, the Deccan Traps occurred in a much less violent fashion, lasting for nearly a million years – perhaps this explains why it was so easy to overlook the event.

Eroded view of Deccan Traps province in India, which occurred at the same time as the extinction of the Dinosaurs.

While there are many arguments for which was the leading cause of the dinosaurs’ downfall, most scientists agree that the coincidence of both these events occurring likely made conditions even more dire on Earth at that time.

If you ignore the current ongoing extinction event, the doom of the dinosaurs during the Cretaceous-Paleogene extinction event is just the most recent major mass extinction event. Going back further in the geological record, there are many other extinction events that have occurred, some even larger than the Cretaceous extinction event.

Causes of these events are endlessly debated, although something geologists and researchers have found difficult to ignore is the prevalence of flood basalt eruptions that occur around the same time as many past extinction events.

Correlations of Extinction Events and Flood Basalt Eruptions

I want to note that there is a correlation here between past extinction events, although that does not necessarily indicate that flood basalt eruptions were always the definitive cause of a mass extinction. With that said, it’s tough to ignore their prevalence in occurring at the same time as an extinction.

Extinction event timeline – Spikes indicate mass extinction events and severity.

The five biggest extinction events by age are:

  • Ordovician–Silurian extinction – 450 to 460 million years ago
  • Late Devonian extinction – 375-360 million years ago
  • Permian–Triassic extinction – 252 million years ago
  • Triassic–Jurassic extinction – 201.3 million years ago
  • Cretaceous–Paleogene extinction – 66 million years ago

While these events are the largest, as can be seen with the bar graph above, there are many smaller extinction events scattered throughout our planet’s very long history as well. The table below shows known extinction events that are correlated with a flood basalt event. The big takeaway here is that there are a lot of extinction events that have a co-occurrence with a flood basalt event.

Exinction Event Name Time Period Associated Flood Basalt Event
Cretaceous–Paleogene extinction event 66 Ma Deccan Traps
Cenomanian-Turonian boundary event 94 Ma Caribbean large igneous province
Aptian Junction 116 MA Rahjamel Traps
Toarcian turnover 183 Ma Karoo-Ferrar Province Flood Basalts
Triassic–Jurassic extinction event 201 Ma Central Atlantic magmatic province flood basalts
Carnian Pluvial Event 230 Ma Wrangellia flood basalts
Permian–Triassic extinction event 252 Ma Siberian Traps
End-Capitanian extinction event 260 Ma Emeishan Traps
Carboniferous Collapse 300 Ma Skagerrak-Centered Large Igneous Province
Late Devonian extinction 375–360 Ma Viluy Traps
Cambrian–Ordovician extinction event 488 Ma Kalkarindji large igneous province

Now, with respect to being scientific, it’s important to understand that correlation does not equal causation. Most flood basalt events can occur for as long as one million years. With that in mind, and with the many past flood basalt events that have occurred, it would only be logical to assume that quite a few flood basalts naturally coincided with periods of extinction.

Another interesting point is that there have been many flood basalt events that have notably not caused extinctions in the past, such as the Columbia river flood basalts, which are the youngest flood basalts on the planet.

Since we do not have a time machine to jump back into each extinction event, determining whether these flood basalts were the true cause of each extinction requires close examination and detailed understanding of how the flood basalts may have caused a massive loss of life on the planet.

For Extinction Events, Climate Change is the Real Culprit

Regardless of whether the cause of an extinction is an asteroid impact, a mass glaciation event, a flood basalt event, clathrate gun blowout, or any other hypothetical extinction trigger, the true underlying theme is that these all kill via climate change en masse.

When discussing flood basalt events, they are one of nature’s most potent agent of climate change. With that said, it’s important to gain an understanding of why certain events may have caused extinctions, whereas other events did not change the planet too much.

It all comes back to Co2 and Greenhouse Gases

In short, volcanoes release carbon dioxide when they erupt, which as we know from our current global warming, is a potent greenhouse gas.

Co2 proliferation in our current global warming scenario may have a lot of scenarios with extinction events that occurred due to flood basalt events. The only difference is that in the current scenario, greenhouse gases have been added at a much quicker rate. The key may be understanding the total volume of co2 in the atmosphere at the peak of flood basalt events, which is not fully understood at this point.

Most carbon dioxide will naturally be sequestered from the atmosphere within a time span of 20-200 years (1). But there is a limit to how much can be removed from the atmosphere at once. In short, if the amount of co2 being added to the atmosphere is higher than the amount of co2 being removed, then the planet will slowly overheat until the point that ecosystems can no longer sustain themselves.

The Earth’s climate typically stabilizes on an abundance of negative feedback loops.  What this means, is that the more an external force tries to change the climate, the more resistant the climate becomes to that change. An example of this is the relationship between plant life and co2. Plants work to gradually remove co2 from the atmosphere, but they also become more abundant in high co2 environments. So as co2 rises in the atmosphere, plant life expands, causing higher removal rates of that co2 in the atmosphere. Traditionally, feedback loops like this make it difficult to cause permanent change, but even feedback loops have a threshold.

If co2 is being added at a high enough rate, such as what we may potentially see during a flood basalt eruption, this may just blow past the thresholds and limits that the negative feedback loops can handle, which would then lead to a dramatically different scenario of runaway climate change.  At this point, there would likely be a chain reaction effect of ecosystem collapse that would initially be triggered by the input of volcanic gases.

One of the common traits many extinction events exhibit is a lack of oxygen in the ocean (known as an Oceanic Anoxic Event). There is direct evidence that flood basalt and volcanic events can trigger these types of anoxic events, much of which is likely a product of global warming as well as changes in the oceanic chemistry as the result of volcanic gases being emitted.

So Why Do Some Flood Basalt Events Cause Extinctions, Whereas Others Don’t?

This is a very valid question, which can be a lynch pin in many arguments for or against flood basalts being the agents of extinction events.

Size Matters

As most would expect, the relative size of the flood basalt eruption is critical. The bigger the event, the more likely it would be to cause an extinction. The Siberian Traps are notoriously enormous, even compared to other flood basalt events, and it’s no surprise that they have been theorized as being the lead culprit during the P/T extinction event, which was the worst Earth has ever experienced.

The Columbia River basalts on the other hand were significantly smaller, and did not cause any mass extinctions.

Co2 removal rate from the atmosphere. As we can see, Co2 is removed at a gradual rate, with a good amount remaining in the atmosphere for a significant amount of time after initial exposure.

Velocity Matters

As we already mentioned, most flood basalt eruptions take place over a long period of time, often lasting as long as a million years. Even once the major flood basalt portions end, the hot spot may live on for millions of years. Since carbon dioxide and other volcanic gases are the main culprit behind climate change, it’s extremely relevant to understand that the speed in which these gases are emitted into the atmosphere can be the singular difference between an extinction or nothing changing on the planet.

As an example, Iceland in many ways resembles our traditional flood basalt events. It has had trap events of it’s own, is extremely large in volume, and regularly exudes basaltic magma and volcanic gases. So why doesn’t Iceland get more concern? The main reason is that the Earth’s atmosphere can remove carbon dioxide from the atmosphere quicker than Iceland can produce it. As a potential flood basalt producer, Iceland simply does not emit volcanic gas at a fast enough rate to affect Earth’s climate and ecosystems in the manner that past flood basalt provinces did.

Graphic depiction of an exposed Icelandic basalt formation. Iceland is a large igneous province, which has been rather prolific over the period of many millions of years. While Iceland represents a flood basalt province in some ways, the rate of volcanic output is not quite high enough to cause long term changes in Earth’s climate.

Some Flood Basalt Provinces Are Likely Gassier than Others

There have been some studies produces that discuss whether gases released during these eruptions would truly be enough to overload the climate with Co2. It turns out that very often, traditional basalt from depth may not have enough Co2 in it alone to causes major changes to the Earth’s atmosphere.

However, massive amounts of hot magma coming up from depth has a tendency to melt, and then drag up a lot of other rocks and minerals as well. Some of these are notably very high in Co2 content. There is some discussion about the rare Carbonatite type magma being especially rich in greenhouse gas, which is often produced when magma comes up from extreme depth in regions of thick continental crust.

Additional to carbonatite magmas, other material can be released during eruptions of flood basalts. During the Siberian Traps flood basalt event, it has been theorized that massive coal deposits were burned during these eruptions, which would have lead to large scale releases of Co2 into the atmsophere on top of what the flood basalts were already producing.

When discussing how the Siberian Traps were able to cause such an incredible amount of global warming, James Muirhead, a research associate in the Department of Earth Sciences at Syracue University, has some profound insights. He states that “Heat from sills exposed untapped, gas-rich sediments to contact metamorphism, thus liberating the massive greenhouse gas volumes needed to drive extinction.”

Additionally, it was mentioned that the composition of the rock and sediment (including fossil fuel type resources) in the crust through which a flood basalt eruption would break through would be a major influence in whether a flood basalt could actually trigger mass climate change, thus causing an extinction event.

The Columbia River Basalt Group – Why They Didn’t Trigger an Extinction Event

As we have touched on earlier, many flood basalt events do  not cause extinctions or mass climate change. The most recent large flood basalt eruption occurred in the state of Washington, in the region where the Columbia River currently runs through. This was another massive outpouring of basalt magma over a long time period, yet it did not seem to kill off many species.

So why did this event avoid causing extinctions, whereas other events like the Siberian Traps, or possibly the Deccan Traps (along with a big impact event) cause mass die-offs?

Note: Some Speculation Ahead

When a hot spot such as Hawaii pushes through oceanic crust, you don’t tend to get highly volatile magma, you simply end up with island shield volcanoes. This is not only true of Hawaii, we can see this on a much larger scale in Iceland as well. In short, oceanic crust is not particularly gas-rich when compared to continental crust, and does not tend to be particularly explosive. Moreso, oceanic crust would be unlikely to have the same amount of co2 bearing materials such as coal, petroleum, limestone, and more locked inside.  (please do correct me if I am wrong here however)

What’s interesting, is that much of the terrain that the current state of Washington is built on these days used to be oceanic crust at one point in the distant geological past. This terrain slowly became accreted as the extinct farralon plate was pushed beneath North America.

What this means, is that while the Columbia River Basalt group erupted on a continental land mass, the land that it pushed through likely did not have the amount of greenhouse gases locked in its sediment that would have caused runaway climate change. The reason being is that a large majority of the land mass it pushed through was actually oceanic crust, and not traditional continental crust.

Summing Things Up

Volcanic trap events and flood basalts can cause extinction events when they overload the atmosphere with co2 and other greenhouse gases quicker than our atmosphere can remove those gases from the environment.

This occurs in a somewhat slow fashion, but the effects can be powerful, and can dramatically alter ecosystems as the climate would presumably become extremely hot.

Sources I Used

S. D. Burgess, J. D. Muirhead, S. A. Bowring. Initial pulse of Siberian Traps sills as the trigger of the end-Permian mass extinction. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-00083-9

Read more : http://www.geologypage.com/2017/07/caused-worlds-greatest-extinction.html#ixzz4oekkzcDn
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http://www.nature.com/nature/journal/v454/n7202/full/nature07076.html?foxtrotcallback=true

http://climatemodels.uchicago.edu/geocarb/archer.2009.ann_rev_tail.pdf 

http://geoscienceworld.org/content/geology/38/6/e210.full.pdf

http://onlinelibrary.wiley.com/doi/10.1029/1999GL900390/full

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