By Afroz Ahmad Shah
Earthquakes and volcanic eruptions are two of the most dangerous natural disasters, which have resulted in immense loss to life and property. However, several volcanic eruptions have also created some spectacular mountains. It is estimated that about 50 or so volcanoes erupt every year, but, only a few severely disrupt human activities. In my previous articles, I had discussed earthquakes and here I will shed some light on the genesis of volcanoes and how they affect us and the environment.
Before the advent of the plate tectonic theory, various geological phenomenons were speculated for centuries together and volcano was one of them. Now, we fairly understand that volcanoes are located along specific tectonic boundaries. These originate within the earth at various depths, where temperature and pressure is sufficient to melt the rock. This usually happens, because as we go deeper within the earth the temperature and pressure rises, for example the temperature within the mantle is about 1300 degree Celsius and since the mantle is a major portion of the earth, a cycling of the heat operates there, which is known as a convection current cycle, which actually transports heat from hotter (deeper) to colder (shallower) regions of the earth. These currents are strong enough to drag the plates and cause them to move, which forms spreading, collision and subduction settings around the globe.
The movement of plates, pressure constrains and the specific tectonic environment causes rocks to melt. Rocks are actually a mixture of different minerals, which have different melting and boiling points. At a certain depth all the rock material melts and forms a molten material, called Magma, this material is hotter, lighter and therefore, tries to escape through some fractures or cracks within the earth. This is greatly facilitated along the pre-existing cracks or along some newly created ones. During a volcanic eruption the material from the interior of a planet reaches the surface and this site is called a volcano. A volcano requires a source of heat and the material to turn into a molten mass. The source of heat within the earth is provided by its radioactive materials and the heat within the core, which was captured during its formation.
The volcanic eruption can occur under oceans or in continents. Iceland is the best recent example of a volcanic activity (Figure). It is totally a volcanic Island that sits astride the Mid-Atlantic Ridge, where the volcanic material is coming from the hot mantle beneath. One of its volcanoes known as Eyjafjallajökull erupted on 14 April this year, for the first time in two centuries. The ash clouds forced aviation authorities of UK to shut down the airspace affected by these clouds for six days. It is reported that most northern European countries also shut their airspace over the period 15-20 April, which affected about 10 million travelers worldwide with a loss of about 2.1 billion Euros. Yesterday, a report was published, which indicates the massive Katla volcano, which has a crater covering 6.2 miles, could erupt soon, this lead experts to issues warnings that Iceland could soon witness its biggest volcanic eruption in 100 years. This could have serious consequences for both Iceland and the world. In the past, a similar volcano erupted in 1783, which killed one fifth of the Icelandic population and half the island’s livestock
The eruption of Mount St. Helens (Figure) occurred in 1980, just after an earthquake of magnitude 5. This triggered a massive eruption and two major landslides. The ash, molten material spread to about 30km from the site and it directly affected about 600 sq km of an area. A debris cloud formed some 26km into the atmosphere.
The Mount Pinatubo volcano on Luzon Island in the Philippines was silent for quite some time and finally erupted in 1991. However, before its eruption hardly anybody realised that there was a monster waiting to wakeup and the historical memory of its previous eruption was also forgotten by the people. The eruption in 1991, in which thousands of people were evacuated and saved, is a good example of rapid geological research in a poor country, which is also substantiated by a prominent shift from a position of almost total ignorance to a scientifically well-informed society. This was because of effective publicity and cooperative authorities, which helped in averting a major disaster.
Contrary to this, there is an African example where a major volcanic disaster can prove fatal if immediate measures are not taken. The volcano known as Nyiragongo (Figure) is a two-mile-high volcano on the eastern edge of the Democratic Republic of the Congo (DRC). It is one of the most active volcanoes on the planet and unfortunately one of the least studied, potentially because of the political conflict there.
In summary, some of the volcanic eruptions are extremely dangerous and pose continuous threats to life and property. The lava, ash and gas can be taken along with the wind and water to longer distances, which ultimately increase the chances of destruction to far off places. The volcanic ash can cause a great damage to air traffic, which was clearly seen during the Iceland eruption (Figure). However, there are some advantages as well; the volcanic soil is rich in minerals, which is very productive. Some volcanoes produce enormous amounts of sulfur, which can be mined, for example in the Andes of northern Chili and some produce geothermal energy, as in Iceland.
It is therefore crucial to study and understand the volcanic systems, so that effective measures can be taken to secure life and to harness the volcanic wealth as a useful source of energy and minerals.
Afroz Ahmad Shah is a research fellow at Earth Observatory of Singapore, Nanyang Technological University, Singapore.