Lake Toba From Space
Credit: Public domain photo from NASA.

Lake Toba fills the caldera of the Toba Supervolcano, [1]and is about 55 miles by 19 miles (88 km by 30 km) in size.[2]

Anticipating the next supervolcanic eruption

There are two natural disasters which are very rare, although they far exceed what we typically encounter in any given year, decade, or century. They are meteor impacts and supervolcanic eruptions.[3]

Meteors can cause the most damage of any natural disaster, and a comet slamming into the Earth is what caused the dinosaurs to go extinct 65 million years ago. The six-miles-in-diameter (ten km) object was the largest to hit the Earth in the past 1.8 billion years.[3][4]

Supervolcanoes are entirely different from ordinary volcanoes, and operate in a different manner. There are more than one thousand active volcanoes on our planet, and many more that are long dormant and could erupt again, although true supervolcanoes are rare and currently just three fully meet the criteria.[5][6]

The last time a supervolcanic eruption occurred was 26,500 years ago, and the last time before that was 70,000 years ago.[5][6]

Let this article inspire you to prepare yourself and your family for disasters. There are many different types of disasters, natural and otherwise, to prepare for, and although supervolcanoes aren't often a threat, no one knows when one could strike. Toba in Indonesia could in fact strike at anytime,[7] as you will read below.

Below I define supervolcanoes. Anyone wanting more explanations about volcanoes should see my article here on InfoBarrel, Types of Volcanoes and Basic Volcanology Terms.

Mount Pinatubo
Credit: Public domain photo.

This is the caldera of Mount Pinatubo, a stratovolcano in the Philippines. In 1991 it caused the second-largest eruption of the 20th century, although it was just 1/100th of official supervolcanic size, expelling about 10 cubic km of material.[8]

Defining a supervolcano: What are they?

As stated above, they are not normal volcanoes, which fall into four types – shield volcanoes, stratovolcanoes, cinder cones, and lava domes. They are something else entirely. They are not volcanoes, they are supervolcanoes.[9]

An ordinary volcano contains a magma chamber and when pressure builds sufficiently, the volcano will erupt. It is similar to filling a water balloon, and letting it fill until it bursts. Supervolcanoes however are different.[9]

A supervolcano has a magma chamber dwarfing the magma chambers of ordinary volcanoes. It sits under the surface of the Earth and slowly fills with more and more magma. Since magma is less dense than solid rock, it slowly rises. Eventually the crust above cracks wide open due to the buoyancy of the magma chamber, and super massive amounts of lava and ash are erupted out. It’s far more than what an ordinary volcano produces.[9]

Besides the way supervolcanoes operate, they are also defined by the amount of material ejected during eruptions. A scale used in volcanology, the science of volcanoes, gives a rating to volcanic eruptions based on the amount of material ejected. It is called the Volcanic Explosivity Index (VEI).[6][5]

The VEI ranks volcanic eruptions from zero to eight. The eruption of Mount Saint Helens in Washington, USA ejected one cubic kilometer of material. This is the minimum amount that qualifies for level five on the VEI.[5]

Level six indicates that at least ten cubic kilometers of material erupted. Examples are Mount Pinatubo in the Philippines in 1991, and Krakatoa in Indonesia in 1883.[5]

Level seven on the VEI indicates that at least 100 cubic kilometers of material were erupted. An example is Mount Tambora in Indonesia in 1815, which is the largest eruption since the end of the last ice age 11,700 years ago.[5][10]

Level eight indicates that at least 1,000 cubic kilometers of material were erupted, and it defines a supervolcano.[5][6] Supervolcanic eruptions are more than six times as large as the massive eruption of Mount Tambora in 1815, an eruption that caused the Earth to have no summer in 1816, and crops and livestock died in much of the Northern Hemisphere, and there was a severe famine that caused hundreds of thousands of people to perish.[11]

There have been supervolcanic eruptions in the past from supervolcanoes that are now extinct. As an example, one erupted in what is now Colorado 28 million years ago, and it will never erupt again.[6]

Lake Toba
Credit: Photo is from Wikipedia by Bernard Gagnon, CC BY-SA 3.0.

Photo taken from the shore of Lake Toba.

The Toba Supervolcano in Indonesia

Indonesia has more than one hundred active volcanoes,[12] and a sizable lake on Indonesia’s island of Sumatra, called Lake Toba, sits in the caldera of a supervolcano.[2]

Taupo in New Zealand has the largest eruption of the past 70,000 years, although 70,000 years ago Toba had the largest eruption of the past 19 million or so years. The Toba Eruption was so large that it ejected more than double what Taupo did 26,500 years ago. Estimates for how much material was erupted are typically around 2,800 to 3,000 cubic kilometers.[6]

This eruption had a huge effect on Earth’s climate for decades or possibly centuries. Many estimates state that the Earth’s temperatures dropped as much as 15 degrees Celsius (8 degrees Fahrenheit) for a few years, and remained 3 to 5 degrees C (1.5 and 3 degrees F) lower for much longer.[13]

At the time of the eruption Earth was in a glacial period, in the midst of the last great ice age, which occurred between 110,000 and 11,700 years ago. The Toba Eruption accelerated the cooling, and about 43,500 years later the eruption of Taupo in New Zealand pushed the Earth’s temperatures even lower.[13][14]

The Toba Eruption covered large portions of South Asia with ash, and heavily damaged forests and wildlife. Most of South Asia received about 15 cm (6 inches) of ash.[13]

The eruption likely had a large effect on humans, and one theory proposes that humans may have nearly gone extinct as a result, dwindling to just 15,000 or so individuals. This theory is much debated, although it’s interesting to consider what the real effect would have been – it certainly would have been large.[13]

Since the supereruption 70,000 years ago, there have been smaller eruptions from Toba, and the most recent is thought to have occurred a few hundred years ago.[2]

Toba Eruption
Credit: Image is from Wikipedia by anynobody, GFDL.

Computer-generated artwork depicting the massive supervolcanic eruption from the Toba Supervolcano.

What if Toba erupts again?

Toba is the biggest worry of the three supervolcanoes (Taupo in New Zealand and Yellowstone in Wyoming, USA are the other two). It sits near a major fault that produced a 9.1 earthquake in 2004 (resulting in a tsunami that killed more than 200,000 people), and an 8.7 in 2005. Even worse is that a large fault runs right through the mountain upon which Lake Toba sits.[7]

The fear is that if the fault shifts, it could suddenly alter the pressure of the magma chamber, and an eruption could occur. Scientists are increasingly monitoring Toba, due to the enormous potential threat it poses.[7]

The possibility of a repeat of what occurred 70,000 years ago can’t be ruled out.[7] An eruption could see ash many feet (meters) thick over at least a 7,000 square mile (18,000 square km) area, ash could rain down across Indonesia and South Asia, and Earth could plunge into a severe volcanic winter with major consequences for all life on Earth.[13]

Okmok Caldera
Credit: Public domain photo.

This is Okmok Caldera on Umnak Island, part of Alaska's Aleutian Islands.

More about volcanic winter

As explained above, the last supervolcanic eruption was Taupo 26,500 years ago.[14] The Pleistocene Epoch ended 11,700 years ago, and since then we have been in what scientists call the Holocene Epoch. In the approximate 11,700 years of the Holocene there has not been a supervolcanic eruption.[6]

The largest eruption during the Holocene was probably Indonesia's Mount Tambora in 1815, which erupted an estimated 160 cubic kilometers of material. This eruption is one of just a few known to have reached level seven on the VEI during the Holocene.[10]

The effects of the Tambora eruption are pretty well known.[11] At the time, the USA had 18 states. It's the year Napoleon Bonaparte was defeated and exiled to a small remote island in the Atlantic Ocean. The eruption caused the Northern Hemisphere to experience no summer in 1816, crops in many locations failed, it snowed in England in June, and there was frost in New York City all summer.[15]

A supervolcanic eruption by definition erupts more than six times as much material out of the Earth as what occurred with Tambora. When a massive eruption puts large amounts of material into the atmosphere and blocks out a portion of the sun's radiation, temperatures reduce worldwide. This is volcanic winter, and it can occur with eruptions not even 10% the size of Tambora. The effect increases with increasing eruption sizes.[16]

The Toba situation discussed above provide a good idea of what may happen with a supervolcanic eruption. Global temperatures could be affected for decades or centuries, and it could have a large impact on all life on the planet.[13][16]