The Toba Eruption
What are supervolcanoes?
Supervolcano warning signs
The Discovery of Supervolcanoes
In 1971 heavy rain fell across most of Eastern Nebraska, in the summer Palaeontologist Mike Voorhies travelled to Orchard and made a startling discovery. He was out in a gulley looking for fossils and he found evidence of a prehistoric disaster with 200 rhinos, camels, horses, lizards and turtles. Dating showed they had all died abruptly 10million years ago. The cause of death was a mystery; the teeth showed the animals had died in their prime.
The skeletons also had a covering of a growth and soft material that was biological. Voorhies sent it away to Karl Reinhard, who decided it was a symptom of lung disease. Every animal seemed to be infected. This meant that there had to be a universal problem – it was ash that had choked these animals to death. Only a volcano could have produced so much ash, but there are NO volcanoes in Nebraska, where the animals were found. One Geologist in Idaho knew of a volcanic eruption dating from the same time. Bill Bonnichsen tied the 2 events together using dating techniques and comparing the ash composition from a supervolcano called Bruneau Jarbridge, 1600km away from the Nebraska fossils! This was an amazing distance and to link the 2 together led to the belief that supervolcanoes exist. This meant that one eruption covered half of America with 2m of ash. These 3 men had made a fantastic volcanic discovery – they had proved that SUPERVOLCANOES exist!
The Toba Super Eruption
The last supervolcano to erupt was 74000 years ago in Indonesia a gigantic volcanic eruption shook the earth. The ash was thrown out 3000km, created global cooling and created a crater larger than the city of London. This super eruption created Lake Toba, 100km long and 50km wide. A global record of sea bed and lake sediment have allowed us to see that the Toba eruption erupted 3000km3 of materialfrom the volcano, 10,000 times the size of Mount St Helens (see the image above). Toba ash reached over 2000km away at depths of 35cm. The sulphur erupted would have converted to sulphuric acid aerosols and cooled the Earth by reflecting the suns energy back to space. A supervolcano such as Toba could reduce temperatures globally by 5 degrees Celsius – enough to spark an ice age and ruin agriculture globally!
Just a few thousand people lived on earth at the time – but what would happen if this struck the USA? A super eruption could affect whole world and badly affect the USA. The USA has a supervolcano in the shape of Yellowstone National Park – but how likely is it that Yellowstone will erupt in our lifetime?
What are supervolcanoes?
A supervolcano is a big bang eruption with the reach to affect everyone living on the planet. Supervolcanoes are hard to spot. Whereas, regular composite volcanoes (such as Mount Pinatubo) have a cone shape, supervolcanoes are depressions in the ground and very hard to spot. The Calderas are so large they can sometimes only be spotted from space and have been identified in Indonesia, in New Zealand, in South America and an extinct one in Glen Coe in England. Yellowstone is still active, and is America’s most famous and popular National Parks. Over 3 million people visit the park every year, but do they know they are visiting a time bomb?
Supervolcanoes are not mountains – they form DEPRESSIONS within the Earth’s crust. They begin with a column of magma rising through a vent into the Earth’s crust. The magma gets stuck and pools, melting the rock around for thousands of years. Over thousands of years the pressure builds up and when the eruption eventually happens it drains the magma lake and the land above collapse down over, creating a caldera.
Supervolcanoes are eruptions and explosions of catastrophic proportions, on the Volcano Explosivity Index (VEI) supervolcanoes are an 8 on a scale that runs from 1 to 8. Each leap up the scale represents an increase of explosive scale of 10 times the power. Mount St Helens was VEI 5!
The volcano at Yellowstone is close to 100km across, and Yellowstone National park has hot springs and geysers and is known to be geothermal. Small eruptions have occurred every 20 to 30000 years at Yellowstone, and it is also certain that there will be another super eruption somewhere on the planet. However, it is difficult to know what to expect from a supervolcano because we have never seen one.
What exists beneath Yellowstone is a hot spot, where magma moves upwards in the Mantle, hits the base of the earth’s crust and melts it creating a huge chamber of magma. The hot spot is static but the Earth’s crust moves over it. There fore there have been many craters across the US caused by this hot spot. 2 million years ago this hotspot settled under Yellowstone. The mountain range around Yellowstone is interrupted by the 2.1million year’s caldera explosion – this swallowed 80 km worth of mountains. Since then, there have been 2 more explosions, 1.3million years ago and 640000 years ago – a cycle of 600,000 to 700,000 years. Are we due another? Scientists don’t know.
What warning signs are there of a Yellowstone eruption?
Norris Geyser basin is one of Yellowstone’s biggest attractions. In 2003 ground temperatures soared to boiling point, geysers erupted more frequently, new vents opened putting out scorching volcanic gasses and mud which killed trees. The Local wildlife suffered, 5 Bison died where they stood. High levels of carbon dioxide and hydrogen sulphide suggested the Bison had died from gas poisoning, both gases come from Magma. There is another sign that magma is rising – ground deformation and land movement. To keep track of the ground movement scientists use GPS and INSAR – which measures the distance between the satellite in space and the ground. This means that they can compare images over time. Since 1996 there has been uplift near the Norris Geyser Basin, and that the land has uplifting over the past 7 years. 2 possibilities - 1.) small injections of magma push up the land or 2.) gas build up from the hydrothermal system push up the land. If it is magma this could lead to a small or huge eruption.
In 1999 a team of USGS scientists mapped the Yellowstone Lake. They found a bulge in the lake floor and explored it with a remote camera and found that the sediments arte lifting up. This could yield a hydrothermal explosion – an eruption under water. Yellowstone is constantly changing so the signs that scientists usually use to predict eruptions are constantly happening so it is difficult for scientists to predict what is happening in Yellowstone. However, the Scientists can use the magma moving to the surface causing earthquakes – 1000 to 3000 small earthquakes happen in the area every year. Seismometers measure these earthquakes. Large earthquakes can trigger eruptions, and could happen in the future, as they allow magma to escape the magma chamber.
To understand the magma chamber the scientists (it was 8km below the ground) used seismometers placed right round the Park (22 in total). These seismometers measured earth tremors, created as the earth responds to movements of magma in the magma chamber. They detect the seismic waves passing through rocks. The waves pass through rock and magma at different speeds, so scientists can check what they pass through based upon the times it takes for the waves to reach the seismographs. They discovered that the magma chamber is 80km long, 40km wide and 8km deep. This huge mass of magma poses a massive threat. This chamber is not necessarily all liquid, but if this does form one single layer of 1000 km3 of eruptible material it could qualify as a supervolcano, Yellowstone has 5 times that. The scientists as yet are unclear as to if these conditions exist.
If Yellowstone erupts it will be disastrous for the whole world. The magma will push the dome up, earthquakes will occur, allowing fissures to crack the surface allowing pressure release, lava to escape and columns of ash to be ejected 10s of kilometres into the air, pyroclastic flows would kill thousands of people. The ash would cover the Great Plains stopping grain production, economic activity in the US would be affected, and global climate would be changed, stopping the growing season. The consequences would be catastrophic.
Exam questions related to supervolcanoes:
(Foundation and higher) Describe the size and shape of a supervolcano (2m)
(Foundation and higher) Describe the likely worldwide effects of a supervolcano eruption. (6m)
The caldera at Yellowstone National Park.
Read the case study below and then answer the exam questions. Answers can be found at the bottom of this article. Click on links to get additional information from around the internet.
What is a supervolcano?Supervolcanoes are on a much larger scale than ordinary composite cone volcanoes (such as Mt St Helens and Eyjafjallajökull). They can be 1000-2500 times bigger than the Mt St Helens eruption!.Supervolcanoes do not look like composite cone volcanoes. They have depressions in the ground called calderas which are often identifiable by a rim of higher land around the edges.
The Yellowstone Supervolcano.
The very forces that created such a unique area such as Yellowstone could also be responsible for its destruction and threaten the existence of people. There is evidence that the huge magma chamber is even more colossal than first expected and that it is shifting. Eruptions have happened in the past, 2 million years ago, 1.3 million years ago and 630,000 years ago.
The truth about Yellowstone BBC documentary part 1
The truth about Yellowstone BBC documentary part 2
Locally the land would be completely destroyed and everything living thing killed. Nationally there will be a loss of 100,000km2 of land and around 90,0000 people may die. The ash would affect transport, electricity, water and farming. Lahars (mud flows) are likely. Internationally the ash would reach the UK in about 5 days. Globally climates would change dramatically, crops would fail and many people would die of starvation.
Watch the documentaries above (in you tube- so will not work in college) to note other more detailed affects of the eruption.