The nature of volcanic hazards is often classified by the violence of the explosion and thus is assigned a number from the Volcanic Explosivity Index (VEI), for instance Icelandic and Hawaiian volcanoes which erupt basaltic lava - which has a low silica content and a basic chemical composition; it reaches a maximum temperature of 2000 degrees Celsius and thus has low viscosity. Due to this, gases are easily released and so the eruptions are non-explosive, with a VEI of 0-1 A prime example of this form is the Eyjafjallajokull volcano in Iceland which erupted in 2010, where during the fissure phase less vicious basaltic lava effusively erupted onto the surface and flowed west – it was also olivine –rich. However the explosive phase had a VEI of 4, hence classified as a large, violent eruption.
On the contrary, Vesuvian and Krakatoan forms have moderate yet explosive eruptions, they erupt andesitic lava which has high silica content and an acidic chemical composition; gases do not escape easily – thus it is viscous – so they build up to produce explosive eruptions with lower temperatures (max. 1000 degrees Celsius). Rhyolitic lava is similar, although it has lower temperatures at around 750 degrees. An example of an andesitic lava eruption is Soufriere Hills in Montserrat which has been actively erupting since 1997. The eruption in 1997 achieved a VEI of 3 (which is significant particularly due to the VEI being a logarithmic scale). Thus based on the nature of volcanic event the Eyjafjallajokull volcano did more damage as it was a lot more explosive.
Furthermore, a volcanic eruption only becomes a hazard if it affects, or threatens people’s lives and property. The impact of a volcanic eruption may be felt locally and globally, and thus can be costly. There are primary and secondary volcanic hazards. A primary effect of the Eyjafjallajokull eruption including lava flows – the lava flow covered an approximate area of 4000m during the fissure phase, whereas during the explosive phase melt water mixed with rising magma which caused it to fragment explosively into large volumes of very fine ash which was ejected (known as a phreatomagmatic eruption) into the atmosphere – another primary effect. The ash plume reached a height of 11,000m into the stratosphere and was swept along the high velocity jet streams between the stratosphere and troposphere towards Europe. The ash caused 107,000 global flights to be cancelled due to the finely grained ash (where 24% was under 10micrometere – similar to aerosol) posing a threat to plane engines.
The ash also affected LEDCs because farmers were unable to sell...