What was the most devastating volcanic eruption in history? Maybe volcanoes likes Mount St.
Helens, Krakatau, or Mount Vesuvius come to mind. After all, there is a reason these names
are remembered till today, decades, centuries and even millennia after their most famous
eruptions. The eruption of Mt. St. Helens of instance killed over 50 people and caused
over 1b$ dollars in damages. Mt Vesuvius famously killed at least 1000 people from Pompeii and
three other roman cities. And the catastrophic eruption of Krakatau killed at least 36000
people But there are of course volcanic eruptions
that are still considerably worse Supervolcanoes like the one beneath Yellowstone
national park for instance which last erupted 630.000 years ago. This eruption was in terms
of material ejected around 50 times larger than Krakatau.
But even that is miniscule compared to what our planet is capable of at its worst.
This is a Flood Basalt Eruption. Even though their name might not suggest it, they are
the largest and most devastating lava eruptions in history. Eruptions so massive they have
again and again changed life on this planet in a way and on a scale like no other natural
phenomenon. To understand how enormous these eruptions
were and what impact they had on Earth and its inhabitants, we have to go on a journey
into the deep past. Intro
Let me take you back in time 252 million years, to the Late Permian Period - Roughly 10 million
years before the appearance of the first dinosaurs. At that time all the continental plates were
fused into one gigantic supercontinent called Pangea. The conditions during this time weren’t
unlike todays. The earth recently had come out of an ice age and the South Pole was still
covered in ice sheets. Over the last couple million years the climate had slowly but steadily
warmed and giant desert areas had begun to form in the center of the continent. Nevertheless,
much of the temperate regions were still covered in huge conifer and fern forests that presented
a wide variety of lush environments for life to exist. Even more than that, life flourished
and diversified resulting in a wide range of new plant and animal species. The rulers
of this era were the Therapsids – mammal like reptiles – that had over the course
of the Permian developed into the dominant life forms on the planet. Among them were
giant predators such as Gorgonopsians, a family of carnivorous Therapsids that were characterized
by their long saber-tooth-like canines and could reach a size comparable to that of lions
or tigers as well as a wide variety of large medium and small herbivores. This was also
the time when the first Cynodonts appeared, the group of Therapsids that would eventually
give rise to the first true mammals some 50 million years later. Amphibians and other
Reptiles were present too in these forests but they were slowly getting relegated to
the sidelines. But that would soon change, because among them you could already find
the ancestors of the first dinosaurs, the group of animals that would dominate the planet
for the next almost 200 million years. In the oceans life was able to develop similarly
unhindered. Even though the formation of the supercontinent had resulted in the drop of
sea levels and the loss of continental shelf regions, what remained of shallow coastal
waters presented an ideal habitat for small and large life forms alike.
This is the scene of the biggest natural disasters in history - a key event that would alter
the planet on such a scale it would forever change the course of evolution.
And it began here – In the North of the supercontinent - in the area that would later
become todays Siberia. Around 252 million years ago an unimaginable amount of molten
rock, risen from inside the earth, had accumulated directly beneath the earth’s crust and was
now at various points beginning to make its way to the surface. The widespread release
of gas from the ground, major and continuous earthquakes as well as the uprising of the
crust by several hundred meters were signs of the impending catastrophe.
It probably started in the north-west of Siberia in the Tunguska Basin, near today’s city
of Norilsk. Over an area of more than 100.000 km² (40.000 mi2) a vast network of volcanic
vents began to open producing huge pyroclastic and phreatomagmatic eruptions with fire fountains
30km or 20mi high and spreading enormous quantities of gas, molten rock and ash across the lands,
which quickly turned a region the size of France into hell on earth. But these weren’t
your typical volcanic eruptions – These eruptions were fed by a gigantic bubble of
magma beneath the crust with a diameter of maybe 1000km or 600mi. And through the countless
rifts and vents that had opened up this magma now began to spread across earth’s surface.
Quickly the emerging lava masses flooded vast areas of today’s Siberia with layers of
molten basaltic rock up to 50m or 160 ft high. A seemingly endless reservoir of magma meant
that each individual lava flow continued for more than a hundred years, burying the land
under up to 2000 km³ or 500 mi³ of molten rock. Additionally, over the centuries and
millennia, ever new rifts and vents meant that magma continued to leak onto the surface
for close to 350.000 years. And so layer by layer the masses of lava were not only spread
over a huge area but also built up to enormous heights
As if the giant lava floods weren’t enough, gases like sulphur dioxide, chlorine and fluorine,
released in vast quantities by the enormous eruptions caused devastation even hundreds
of kilometres away. Basaltic lavas are especially rich in sulphur dioxide. When released into
the atmosphere it reacts with water vapour in the air to form sun blocking aerosols.
These aerosols can for months – sometimes years – result in a significant temperature
decrease – a volcanic winter. Acid rain, the result of the condensation of hydrogen
chloride and hydrogen fluoride, can cause burns and poising in plants and animals that
come into contact with it. Additionally, Fluorine and Chlorine can cause damage to the ozone
layer, potentially exposing vast areas to dangerous UV-radiation that can cause tumours
and gene-defects. Although all these gases are typically removed from the atmosphere
rather quickly, the prolonged nature of the volcanic eruptions in Siberia meant the destructive
potential of them was constantly renewed. When the lava flows eventually stopped, the
floods had buried an area of more than 4.000.000 km² or 1.500.000 mi² - so an area half the
size of the United States– under a layer of lava more than 2 km or 1 mi thick.
But despite the incredible destruction this catastrophe had caused in the North of the
supercontinent over the past 300.000 years, the rest of the Pangea as well as in the oceans
were relatively unaffected by it. But that would soon change.
Because what on the face of it looked like the end of the large scale volcanism in Siberia
was only the beginning of a second much more catastrophic phase, which was looming hidden
beneath the now solidified masses of lava. The trillions and trillions of tons of volcanic
rock that were now bearing down on the earth’s crust acted as a giant lid that prevented
more of the still abundant magma inside the ground to rise up to the surface. With no
way up the magma instead began to force its way laterally into the rock, creating a huge
underground network of sheet like horizontal intrusion so called sills. This network began
to heat up an enormous area of continental crust like a giant underfloor heating system.
As the hot magma came into contact with the volatile-rich sediment of Permian Siberia
vast quantities of organic and inorganic CO2 were freed from the rocks. Additionally, the
destruction of pre-existing oil and coal-bearing deposits by the sill intrusions released even
more gases. When the sills eventually reached the boundaries of the lava province and found
their way to the surface, these gases were released all at once in one catastrophic pulse
– maybe up to 100.000 GTs of CO2 got released into the atmosphere.
This had far reaching consequences for the climate, which this time weren’t limited
to the northern hemisphere – the entire planet was affected. Almost instantly the
global average temperature rose by 5°C or 9°F – the result of catastrophic global
warming. Compared to the daily weekly and seasonal temperature variations we experience
constantly 5° might not sound that much but yearly global averages are much bigger deal.
During the last ice age when much of North America and Europa were buried under more
than a kilometre of ice the global average temperature was only about 5°C lower than
it is now. So you can imagine what consequences a jump of 5°C in the other direction must
have had. And this was only the beginning, as the warming
of the oceans soon would set off of a chain reaction that would raise temperatures by
another 5-10°C or 18°F – Through the release of oceanic methane. At the bottom of the oceans
along the continental slopes there exist immense reserves of frozen methane, so called methane
hydrate. This methane was produced by tiny microbes as a metabolic by-product over millions
of years and was then at depths of over 200m or 650 ft frozen into ice crystals through
high pressure and low temperatures. That way, it is stored stably and safely for long times.
It is however very responsive to changes in the environment particularly to changes in
temperature and so 252 my as the result of the warming of the oceans vast quantities
of methane got released into the atmosphere as big portions of the methane hydrate deposits
melted. Like CO2 methane is a greenhouse gas – its effect in the atmosphere are however
30-86 times stronger and so the planet subsequently warmed another 5-10° - to a total of 15°C
or 27°F This cataclysmic temperature increase transformed
the planet from a lush paradise into a barren hellscape. Imagine the Northern United States
or the UK at temperatures like the Sahara or tropical ocean temperatures of over 40°
or 104°F Because of this intense heat most of the plant
life perished, the large temperate forests all but disappeared and the desert areas that
before had only existed in the center of Pangea began to spread across the entire continent,
killing everything that wasn’t adapted for life in such harsh conditions.
Most of the few land animals that survived were small generalists that could survive
on little water and weren’t too picky about their food. Many of them were only able to
survive these extreme temperatures because they lived in underground in burrows. Our
ancestors, the Cynodonts, were one of these few survivors.
The oceans were affected even worse. The enormous amounts of CO2 in the atmosphere resulted
in a similar increase in oceanic CO2. As a consequence, the PH level of the water dropped
and the ocean acidified. This made building exoskeletons, shells or other calcium carbonate
structures increasingly difficult, making animals that need these structures to survive
like corals, zooplankton and shellfish the first major victims of the crisis.
At the same the ocean began to lose its oxygen. Warmer water can hold fewer gases than colder
water so large scale ocean anoxia was the result. Like a goldfish in a glass left out
in the sun, entire species and of animals suffocated because of this. These conditions
also promoted the development of anaerobic bacteria, which only thrive in oxygen-depleted
environments. Instead of oxygen, these bacteria produced hydrogen sulphite, a highly toxic
gas that poisoned the water Initially these effects were limited to shallow
coastal waters but as due the warming of the Polar Regions the ocean currents were disrupted
the entire ocean was affected. What remained of the largest ocean in history was a stale
toxic oxygen depleted graveyard. In the end the volcanism in Siberia had transformed
the planet from an oasis of life into the largest mass grave in history.
Within only 60.000 years, the global animal population had decreased by more than 99.9%.
95% of all species in the ocean and 75% of all species on land died out. The end Permian
extinction was the biggest extinction in earth’s history and only one that almost wiped out
all land plants and also severely affected insects
It would take Life on earth almost 10 million years to fully recover from this catastrophe.
But while the formation of this so called “large igneous province” had brought complex
life to the brink of extinction it was also a new beginning for the few animals that survived.
Like an evolutionary reset-button it had reshuffled the deck and gave those species that had managed
to fight through the inferno the unique opportunity to conquer the earth. What group of animals
made best use of this chance is probably needless to say
With an area of maybe more than 4.000.000 km² and a volume of around 3-4 million km³
- That’s enough lava to cover all of today’s land area with a layer of rock 10m 32ft thick
– the province in Siberia, also called the Siberian Traps, is definitely one of the largest
of these provinces, but it’s certainly not the only one.
Large igneous provinces are defined as magmatic plateaus that span over 100.000 km² or more
and have a volume of at least 100.000km³. By that definition we know at least 40 of
these provinces from the last 540 million years alone, of which about a dozen probably
exceeded the definition by at least 10-fold. Of course erosion and tectonic processes have
in most cases weathered away or destroyed a lot of it making estimations of their original
extent challenging, but the fact that you can still see the astonishing remnants of
these eruptions today - in some cases hundreds of millions of years after their formation
– speaks to scale of these eruptions. We can divide large igneous provinces into
continental and oceanic provinces; our record of oceanic ones is however limited because
as opposed to continental plates the oceanic crust is constantly getting recycled by tectonic
processes and is therefore with rare exceptions nowhere older than 180 million years.
The most notable of the oceanic provinces is probably the great ontong java plateau
in the south west pacific. It consists of a series of provinces that during their formation
120 million years ago probably made up one enormous plateau. Here, over an area the size
of Australia, the largest lava eruption in the last couple hundred million years took
place. Over the course of 7 million years a total of 80.000.000 km³ of basaltic lavas
were expelled. That is enough lava to bury the entire United States under 10km or 6mi
of molten rock.. On land we have – aside from the Siberian
traps – for instance the Central Atlantic magmatic province that formed 201 million
years ago in the center of Pangea, before the subsequent breakup of the supercontinent
scattered it across three of todays continents. Its original extent is estimated to have covered
between 7-11 million km² making it in terms of area the largest of the continental provinces.
In Asia we can also find the remnants of the Deccan Traps, an up to up to 2km thick province
that once covered half of modern India. It formed 66 million years ago at the end of
the cretaceous period. The North Atlantic igneous province in Europe
is between 55 and 60 my old and was later broken up by the opening of the North Atlantic
Ocean. With an original volume 2-3 larger than that of the Siberian traps it is perhaps
the most voluminous continental province. At last we have Columbia River Basalt Group,
a comparably small large igneous province in the western United States. Only between
17-6 million years old is one of the youngest and best studied provinces on earth. Today
it remnants stretch across 4 states, cover an area of 160.000 km² or 60.000mi² and
reach a thickness of roughly 1.8 km or 1.1m Of course, these are only a few of the dozens
of provinces that we know of. Considering the devastation the Siberian Traps
caused, it’s perhaps interesting to examine what impact the formation of some of the other
mentioned provinces had on the planet. What causes these catastrophic lava eruptions
also remains to be answered. All of this will be part of the second video
on Flood Basalts.