by Chris Phoenix Clarke
Volcanoes are pretty badass, let’s be honest. In this particular blog I’ll be reviewing 5 of the most destructive natural events in Earth’s history, caused by 3 different volcanic mechanisms: stratovolcanoes, supervolcanoes and flood basalt eruptions.
Everyone’s typical picture of a volcano is a tall, conic mountain with a crater at the top bellowing out ash and spewing out lava (a stratovolcano – see picture of Mount Fuji below). Unfortunately, this is no more accurate than the stereotypical view that the English all drink tea and talk like the Queen, and Australians converse solely about barbecues and drink Fosters.
There are many different types of volcano, ranging from the picture-postcard snow-crested peak of Mount Fuji in Japan (below) to the linear fissure vents of Iceland and Hawaii. Some explode violently sending gas and dust high into the atmosphere, whereas some seep thick lava down gently-sloping flanks (known as shield volcanoes). Others have enormous calderas — the area of a volcano that collapses in on itself and into the empty magma chamber following an eruption, leaving an incredibly vast, open, cauldron-like hole. Volcanoes of this type and size are usually coined supervolcanoes, but are classified officially on their VEI rating — the Volcanic Explosivity Index — a logarithmic scale with each rise of 1 corresponding to a ten-fold increase in the amount of ejected material, with the highest rating being an 8; the lowest being a zero).
Some volcanoes lie patiently dormant while others have died and gone to volcano heaven (or hell, shall we say) and are extinct. Some volcanoes can even erupt for a million years and take centre stage in the largest mass extinction event our planet has ever known: the Permian-Triassic extinction event. Said to have wiped out 90% of all living things, this catastrophe of 250 million years ago very nearly ended life on Earth before humans had even begun to evolve.
What follows are 5-of-the-best eruptions, so to speak, but one must remember that although fascinating, volcanoes are also furnaces of death and destruction and should be regarded equally with fear and caution as with curiosity and awe.
5) Mount Tambora, 10th April 1815. Location: Sumbawa, Indonesia. VEI rating: 7
Officially the largest eruption in recorded history, Mount Tambora is claimed to be the only VEI-7 in almost 2000 years. It killed in excess of 70,000 people and caused 1816 to become known as the ‘year without a summer’ due to the effect it had on North American and European weather. The lowering of global temperatures was such that crops failed and animals died, causing widespread starvation – the worst famine of the 19th century.
This volcanic winter, as it is known, is the reduction of global temperatures as a consequence of ash particles and sulphuric acid droplets physically blocking sunlight from reaching the surface of the Earth.
The eruption was heard over 2000 km away and the ejected material (ejecta) from the volcano measured over 160 km3 .
Mount Tambora is still active to this day, but almost reaching the 200th anniversary of the catastrophe it hasn’t shown any signs of exploding again with the same magnitude.
4) Yellowstone caldera, 2.1 – 0.64 million years ago. Location: [currently] Wyoming, United States. VEI rating: 8
Like the pits of Hell portrayed in Dante’s Inferno, here lurks a reservoir of fire and brimstone in the heartland of the United States that has been responsible for many of the largest explosive volcanic eruptions in all of history. I am, of course, talking about the now world-renowned Yellowstone hotspot.
90% of the planet’s volcanic activity is found at the boundaries between tectonic plates; the other 10% at hotspots.
Hotspots are areas of volcanic activity at seemingly random locations across the surface of the planet that are hypothesised to be caused by anomalously super-hot parts of the underlying mantle or particularly-thin sections of the Earth’s crust (or, indeed, both).
While the hotspots do themselves appear to drift very slowly (the mantle behaves like a highly-viscous liquid over geological time), the constant, and comparatively faster, movement of the tectonic plates which make up the crust move across the hotspots — tracing out a trail of volcanic structures above and away from them. This is evident in island chains such as Hawaii and on land from the Yellowstone hotspot trail. As the Pacific Plate has headed in a north-westerly direction over the last few tens-of-millions of years, the magma from the hotspot has intruded through the seafloor to build up volcanic islands that rise above sea level.
Once an island is formed it is very gradually dragged away from the hotspot by the tectonic plate until it is no longer positioned above the active area. The process continues on and another island is made in its place — repeating again and again until an island chain starts to take shape. The main island of Hawai’i is the newest (300,000 years old) and the oldest is the island of Kaua’i (4 million years old), but the chain actually stretches away from what is termed as the state of Hawaii all the way up to the Aleutian Trench near Russia — the eroded islands there being many tens-of-millions of years old.
On land, the Yellowstone hotspot has erupted nearly 20 times in the
last 16.5 million years, with the trail of calderas originating at the Nevada-Oregon border, going right across Idaho and finishing at its current location at the most north-westerly tip of Wyoming — in Yellowstone National Park (if only Yogi Bear was made aware of the real nature of his surroundings!). Fast-forward a little longer and a new caldera will undoubtedly form in Montana.
Inside the national park the Yellowstone Plateau consists of 3 calderas that date back to 2.1, 1.3 and 0.64 million years ago — the first and last of these being supereruptions, and the other a very sizeable VEI-7 (getting on twice the size of the Mount Tambora eruption of 1815). The ejecta from the two supereruptions was approximately 2,500 km3 and over 1000 km3 , respectively, making the former the second largest VEI-8 eruption of all time.
3) Krakatoa, 26th August 1883. Location: Sunda Strait, Indonesia. VEI rating: 6
The second, but unfortunately not last, entry on our list from the Indonesian archipelago, Krakatoa is largely regarded as the most notorious eruption in recorded history. Having claimed the title as the loudest noise ever heard by human ears and creating the biggest tsunami wave ever seen with human eyes, it also has the rather more infamous statistic of killing approximately 120,000 people (figures of 36,000 made 130 years ago are alleged to have been grossly under-estimated) — a total that is probably the most number of human fatalities ever caused by a volcanic eruption.
Having only been a VEI-6 eruption, you might be wondering why Krakatoa was so devastating. The truth is that no one really knows. The favoured hypotheses suggest that some form of subsidence or landslide, either above ground or submarine, allowed the mixing of sea water with the volcano’s magma chamber causing a highly energetic phreatic explosion. Either way, two thirds of the island disappeared overnight as a result of the cataclysm.
Such was the ferocity of the main explosion that sailors in the Sunda Strait had their ear drums shattered, and the noise could be heard as far away as Australia (over 3000 km away) — a distance that is comparable to travelling between London and Moscow!
The pressure wave caused barometers the world over to go crazy and reverberated around the world 7 times; the explosion having had the energy of 2 hundred million tonnes of TNT (or 200 megatonnes) making it 12,500 times more powerful than the bomb dropped on Hiroshima and 4 times as powerful as the largest nuclear device ever detonated (the Russian Tsar Bombe in 1950).
But the two most deadly features of the Krakatoa explosion were the tsunamis and pyroclastic flows that followed. A pyroclastic flow is a superheated, fast-moving cloud of noxious gas and dust that incinerates and suffocates as it propagates away from a volcano, sometimes for many tens, or even hundreds, of miles. Indeed, the one generated by Krakatoa traversed 40 km of ocean on a cushion of heated air and inundated flabbergasted natives on the island of Sumatra, killing over 1000 people.
The tsunami surges reached their peak at 40 metres — some 3 to 4 times higher than the Boxing Day tsunami of 2001 and Japanese tsunami of 2011. Tidal gauges registered increased levels as far away as the English Channel (although some scientists claim this was due to the globally circumnavigating pressure wave). It was the sheer immensity of the flooding that caused over 90% of the deaths from the catastrophe.
Never before has humankind played witness to oceanic destruction on such a colossal scale. The sight must have been truly terrifying. It is therefore understandable that Krakatoa makes it into the top 3 eruptions of all time.
2) Lake Toba, 70,000 b.c. Location: Sumatra, Indonesia. VEI rating: 8
The eruption at Lake Toba (also situated in Indonesia) is widely recognised as the largest volcanic event on Earth in the last 25 million years and the largest VEI-8 of all time. Considered supervolcanic due to its VEI rating, the explosion ejected approximately 3000 km3 of material into the atmosphere, blanketing most of southern Asia in 15 cm of ash and causing a volcanic winter that lasted for nearly a decade. Moreover, it is postulated that global temperatures didn’t recover fully for a further 1000 years (there is geological evidence in ice cores of dramatic and catastrophic climate change during this period).
But possibly the most extreme part of Lake Toba’s CV is the suggested ‘human bottleneck’ that ensued. Homo sapiens were only just beginning to get itchy feet by considering to venture out of Africa at the time, and along with the other hominids (including the Neanderthals) it made for a pretty meagre world population. The Earth was experiencing a glacial period (between 110,000 – 15,000 years ago) so technologies such as agriculture were far from being realised and to put it simply: humans hadn’t been around long enough to populate to anything resembling considerable numbers.
After the Toba catastrophe it is estimated that less than 10,000 humans remained on the planet. Global temperatures — already low due to the glacial period — had dropped by 3-5 °C courtesy of the volcanic winter, and in doing so created more planetary ice cover, which in turn raised the Earth’s albedo (a measure of how reflective to sunlight a surface is) — further compounding the problem.
It is any wonder we managed to survive at all and quite scary to think we very nearly faced extinction as a species. For this reason Lake Toba makes it to number 2 on our list.
1) The Siberian Traps, 250 million years ago. Location: [what is now] Siberia, Russia. VEI rating: n/a
The Permian-Triassic mass extinction (or ‘The Great Dying’ as it is commonly referred to) is the single largest extinction event since the emergence of multicellular life on Earth.
Wiping out 90% of all living things, The Great Dying has often been attributed to a gargantuan asteroid impact (far larger than the one responsible for the death of the dinosaurs) or a volcanic eruption of almost incomprehensible enormity and duration.
It just so happens that an enormous volcanic event did occur around the same time, in what is now known as Siberia, Russia (the continents had very different geography hundreds of millions of years ago) — creating the Siberian Traps. Covering an area of 2 million square kilometres (the size of Western Europe) the Traps are evidence of an eruption so massive that it spewed out up to 4 million km3 of lava! The Earth literally split open in a number of different places and the magma inside bled out for — wait for it — one million years. That’s one million years in case you didn’t hear me the first time.
The word ‘traps’ is derived from the Swedish trappa (meaning stairs) and is an example of a flood basalt. This type of event is the massive eruption of lava over a wide area of land or ocean that creates huge plateaus and mountain ranges — often layered in composition and forming ridged edges that resemble stairs or steps (see below).
It’s unclear why this event took place; the best hypothesis supposes that a meteorite impact triggered the enormous splits to open, and is also backed by [literally] solid evidence. A number of candidate craters have been discovered — the best situated in east Antarctica. The crater is 500 km wide and is still intact, suggesting it was formed in the last few hundred million years. It would have also been roughly antipodal to the placement of the Traps, meaning it is at the opposite location on the other side of the Earth. The theory is controversial at best but some scientists hold that an impact on one side of a planet can affect its antipodal location — as if the force propagates along a straight line through the centre of the Earth connecting the two. Either way, an impact of this size would doubtless trigger tectonic unrest the world over, causing massive volcanic activity.
Whether initiated by colossal asteroid or gaping fissures in the crust, or a combination of both, The Great Dying very nearly extinguished all life on Earth. The flood basalt of the Siberian Traps is inextricably linked with the worst extinction event in history and is without doubt the most massive example of volcanic activity on the planet. It is for this reason that it tops the list of the most notorious eruptions ever; a real volcano apocalypse — evident in the cold, icy plateaus of northern Russia.