Published on April 16th, 2010 | by Yellow Magpie5
Volcanoes: Force Of Nature And Wonder
A sea of red almost as bright as the Sun bubbles and gurgles in a huge melting cauldron. When the time is right the cauldron will get too heavy, too full. Too much pressure.
A noise that would deafen the sound of 100 Super Jumbos casts its mighty roar. The heavens open, a giant explosion rips through the surface of the Earth sending masses of material into the sky. And then…darkness engulfs the day.
Volcanoes are one of the most powerful forces of nature on Earth. They can cause islands to appear out of the ocean and can also do the exact opposite, force them to disappear into the sea. One of the most awe-inspiring of sights, they can cause great catastrophes and induce mass panic.
Creation Of Volcanoes
Volcanoes are created by ruptures in the Earth’s crust. Fuelled by pockets of molten rock deep underneath the surface called magma, volcanoes allow lava and ash to escape from deep underground in powerful explosions. Magma that manages to break the surface is known as lava.
Volcanoes are generally found where there is tectonic activity. Typically, this activity is a result of either diverging (moving apart) or (converging moving towards) plates. The Mid-Atlantic Ridge is an example of diverging plates while the formation of the Pacific Ring of Fire is a result of converging activity.
Thinning of the Earth’s crust can also result in the formation of volcanoes as in the case of the African Rift Valley.
Largest Known Eruption
The Greek Island of Santorini erupted with five times the power of Krakatoa in 1470 BC. The entire island was completely destroyed due to the tremendous force of the explosion. A gigantic tidal wave that was created in the aftermath of the eruption caused havoc to the neighbouring island of Crete.
Explosive And Non-Explosive Volcanoes
There are two main types of volcanoes in terms of impact. Explosive and non-explosive.
Explosive volcanoes tend to be highly dramatic and cause a great deal of damage. While non-explosive volcanoes are generally deemed to be safer and less dangerous. The key difference between the two lies in the composition of the magma. Magma that is thin and lacks viscosity is unlikely to explosively erupt. These types of volcanoes typically erupt on a regular basis. There are generally believed to have a low concentration of silica.
Explosive volcanoes on the other hand, are generally the result of underground activity and the collision of tectonic plates. Magma in these types of volcanoes is thick and has large quantities of silica in its composition.
Magma that contains silicates have a tendency to be viscous. The viscous magma thereby plugs the volcano vent. Over time pressure builds and once the magma plug cannot hold the force, the volcano erupts with explosive consequences.
Explosive volcanoes send out masses of lava bursting from the vent and emitting ash and toxic gases into the air in a lethal pyroclastic flow.
Volcanic ash is also deadly killer. Ash, which is created by the tremendous heat and force of an eruption, gets sucked up into the atmosphere where it can rain down many kilometres away from the crater. This was largely responsible for the death of the people of Pompeii in Italy.
Benefits Of Volcanoes
Although the exact role of volcanoes is not fully understood, their destructive aspect is countered by the many benefits that they also bring. Volcanic activity has resulted in new land masses forming where previously there was only water and sea.
In November, 1963, a volcanic eruption off the coast of Iceland created a new island called Sertsey. All of Hawaii was created by the same processes.
Snowball Earth And Volcanoes
It is believed that the Earth was covered in an all-enveloping layer of snow millions of years ago.
‘Snow-Ball’ Earth, as the phenomenon is coined, is a theory that the Earth was completely ice encrusted between 650 to 750 million years ago. It is thought that a series of volcanic eruptions freed the Earth from its icy tomb and allowed life to flourish.
After volcanoes freed the Earth an unrivalled period of growth and life began on Earth. For the first time, complex, multi-cellular organisms emerged from their single-celled offspring. Life would never be the same again.
Largest Active Volcano
The largest known active volcano is Mauna Loa in Hawaii. With a crater 3.5 kilometres (2 miles) in diameter, its latest activity was in 1984. As there is a lack of silica present, the lava has little viscosity and flows like a fluid liquid. Because of this and the low profile of its sides it is known as a shield volcano.
Supervolcanoes are large volcanoes that have the potential to cause enormous devastation on a large if not global scale. Their huge size poses potential difficulties for people and wildlife on Earth.
If such volcanoes did erupt, large amounts of sulphur and ash would penetrate the atmosphere causing the sun’s rays to be blocked. Yellowstone National Park is said to be home to a Supervolcano with the potential to obscure sunlight across the world if it does erupt.
Toba The Last Supervolcanic Eruption
One of the great mysteries that puzzled scientists and geneticists for years was the relative lack of diversity in the Indian population dating back to roughly 74,000 years ago. The only other race that had such low diversity was the Native Americans and this could be explained by the fact that were cut off from the rest of humanity by the American Continent.
However, India had no such geographical restrictions and the mystery deepened.
Finally, it emerged that a Supervolcano of a similar size as Yellowstone’s erupted 74,000 years ago in Indonesia.
This eruption was enormous. Vast clouds of ash and dust breached the Earth’s atmosphere and some even made it as far as Outer Space. All of this ash travelled west raining down upon India covering much of the land in a carpet of ash.
This layer of ash caused much turmoil and the Indian people would have faced grave starvation.
Volcano Classification In The Popular Imagination
There is a widespread belief that volcanoes can be easily classified as active, dormant and extinct by their frequency of eruption. Active volcanoes are deemed to be active if they have erupted regularly in the past.
Dormant ones are those who have erupted in recorded times. Extinct volcanoes are ones which not erupted in recorded times.
However, these models are not accurate and have shown to be wrong on more than one occasion.
The Reality Of Volcanoes
In reality, volcanologists consider extinct volcanoes to be ones which have either exhausted or do not have a sufficient lava supply. As a result these types of volcano are deemed unlikely to erupt.
However, even extinct volcanoes can become active by regaining a supply of lava which is possible due to constant changes in the Earth itself. As volcanoes can remain dormant for millions of years, scientists find it difficult to distinguish between these and active volcanoes. Previously-thought-to-be-dormant volcanoes have erupted back into life.
One such example is Soufriere Hills, Montserrat, Bermuda, which became active in 1995. Fourpeaked Mountain, Alaska, is another notable volcano which was long thought to be extinct but which erupted in September, 2006, after nearly 10,000 years of dormancy.
Iceland’s Eyjafjallajökull Volcano
On March 20, 2010, after months of geological activity (including several small earthquakes) Eyjafjallajokull (pronounced AY-yah-fyah-lah-YOH-kuul) erupted. This initial eruption was quite small and caused minimal disturbance.
However, worse was to follow and on April 14, 2010, a more serious eruption resulted melting a large ice-covered glacier. The meltwater which emanated from the glacier in turn caused flooding which led to over 800 people evacuating their homes.
Dangers Of Ash To Aircraft
The ash plume represents severe danger to airplane jets for several different reasons:
- The ash can sandblast both the windows and landing lights of the plane hindering landing and reducing visibility.
- It can interfere with the plane’s navigational instruments such as radio and air speed indicators.
- Volcanic ash can also cause engine failure as it has a tendency to stick to the engines causing them to malfunction.
As the ash plume is ejected by the volcano at a high altitude, the very same altitudes that jets cruise at, it represents a significant threat to flying.
Eyjafjalljakull has caused severe disruption to the aviation industry in Europe. As it is incredibly dangerous to fly in such conditions, much of the flights have been grounded as a result. The worst affected have been Ireland and Great Britain, while aircraft in Northern Europe and parts of Spain and Portugal have also been forced to remain on the ground.
Ireland and Great Britain
Although there are no volcanoes that are considered to be active in the United Kingdom there are several extinct ones. Most notable is Croghan Hill, near Tullamore, County Offaly in Ireland. The remains of an extinct volcano, it is over 26 acres in area and rises some 234 metres (767 feet) in height.
Given what we know about volcanoes it is unlikely that those we consider extinct will continue to be so in the millennia ahead.
Peter Francis and Clive Oppenheimer’s Volcanoes is a comprehensive read, at over 500 pages, on the subject. It lists some of the controversial theories on the functions of volcanoes and the potential impact into the future as well as providing fascinating accounts of how eruptions occur.
Managing to explain the current knowledge of the inner workings of volcanoes in an easy to understand manner without ever resorting to condescension is difficult but Oppenheimer and Francis pull this off marvelously well.
Fisher, Heiken and Hulen’sVolcanoes: Crucibles of Change provides a shorter read at just over 300 pages but covers all the bases in this offering from the volcanologists.