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There are links down the right hand side to other posts which, may I say, I'm sure you'll find just as interesting :) - I'd suggest taking a look at the post on Supervolcanoes!

Simply a site about geography, for geography lovers.

The Supervolcano: The Most Destructive Force on Earth

Supervolcanoes are different from normal volcanoes. They aren't recognisable by a conical shape that you would imagine a volcano to be. These volcanoes form calderas which are huge craters in the ground after previous eruptions, which are so large that they are often only noticeable from the air above.

A supervolcano is the most powerful known destructive force on the planet. Only asteroids or other astronomical events are potentially powerful enough to exceed their magnitude. They have became famous due to Yellowstone National Park Volcano in the USA, so much so that there has even been a whole supervolcano dvd covering Yellowstone Park information.

Yellowstone Supervolcano Caldera: 

Eruptions are much more powerful than a normal volcanic eruption as the magma concentrates and builds pressure just beneath the surface (as little as 5km) in massive magma chambers where the dimensions are measured in kilometres - which gives an impression of how big these things are! Normal volcanoes form where magma forces its way up through cracks in the crust along destructive plate boundaries (high energy eruptions) and along constructive boundaries (low energy eruptions), and erupt frequently in geological terms. Supervolcanoes form where this magma is stopped from reaching the surface; it melts the surrounding rock and the chamber grows in size and pressure.

"A supervolcano - a volcano capable of producing a volcanic eruption with ejecta greater than 1000 cubic kilometres. This is thousands of times larger than most historic eruptions."

Once this pressure exceeds what the thin crust can take, it breaks through in with incredible force chucking out insane volumes of ash and magma into the upper atmosphere. This causes a volcanic winter as the ash creates a screen around the Earth bouncing off sunlight, turning days to night and summers to winter. Ash covers the ground killing plants and in turn, the animals through starvation and suffocation. After the eruption, the ground collapses at the site of the eruption into the de-pressurised magma chamber and forms the huge caldera.

The last supervolcano event was the Toba super-eruption in Indonesia was between 69,000 and 77,000 years ago:
  • It plunged the whole planet into a 6 - 10 year volcanic winter
  • The human population crashed to below 10,000 on the entire Earth, possibly as low as 1000 breeding pairs 
  • 2800 km3 of magma was ejected, of which 800 km3 fell as ash, although due to recent deep-sea cores, this is views as an underestimate.
  • Although the eruption was in Indonesia, the ash that was ejected, when it fell, covered the entire surface of South Asia in a layer of ash 15cm thick. Even more ash was deposited over the Indian Ocean, and the Arabian and South China Sea.
To put 2800 km3 of magma into perspective: If the whole of the United Kingdom was buried with that volcanic material, it would be buried to a depth of 11.53 metres. 

Evidence which gave light to the population crash at this period came from many DNA studies which show a drastic drop in genetic biodiversity after this period, known as a 'bottleneck' effect. 
Note: The population crash has been linked to the Toba super-eruption but causation can't be proven.

Nowadays, Toba caldera is a large lake 100km long and 30km wide, but underneath the active volcano is hidden while the magma chamber slowly fills back up building up to another super-eruption. Lake Toba is one of the largest calderas on the planet.

Lake Toba caldera:

Worryingly, we are overdue for another supereruption. Yellowstone supervolcano in Yellowstone National Park, USA, is overdue for it's next eruption. Scientists have found, by analysing minerals within surrounding rocks, that it erupts on a regular cycle every 600,000 years - but there hasn't been an eruption in 640,000 years. It has been suggested that the next eruption could be 2,500 times the size of the 1980 Mount St. Helens eruption which was the deadliest and most economically destructive volcanic event in the history of the United States where 57 people died.

The magma chamber is thought to be around 80 kilometres long and 40 kilometres across, to a depth of 8 kilometres. All this is lying only 8 kilometres below the surface, straining to be released. Volcanologists from the University of Utah, who are measuring and studying the area, have calculated that the ground above the magma chamber has risen by over 70 centimetres in some areas since the year 2000.

An interferogram showing a map view of ground movements at Yellowstone:


The black dotted line shows the area of uplft, each colour represents a contour along which there was equal uplift of the ground. This is based on in information gathered between September 2004 and August 2006. As you can see from the scale in the bottom left, this is a huge area this is being forced up, this means the magma chamber is expanding, and there has also been an increasing frequency of earthquakes recently. This may be warnings of an eruption in the near future. There are many contrasting theories on when eruptions will take place and what the warning signs (if any) will be, which isn't very relieving!

Further Reading:

A quote to have a think about:
Each volcano is an independent machine—nay, each vent and monticule is for the time being engaged in its own peculiar business, cooking as it were its special dish, which in due time is to be separately served. We have instances of vents within hailing distance of each other pouring out totally different kinds of lava, neither sympathizing with the other in any discernible manner nor influencing other in any appreciable degree. 
(Clarence Edward Dutton in a 'Report on the Geology of the High Plateaus of Utah' in 1880)

The GeoMessenger


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    Additionally, I bet you didn't know Bath was built in an extinct volcano...

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