Analyse the Factors That Cause Differences in the Hazards Posed by Volcanoes Around the World

‘Analyse the factors that cause differences in the hazards posed by volcanoes around the world’. (40 marks)

There are variations in the form, frequency and type of volcanic eruption. These are related to the different kinds of plate margin, emissions and lava. A volcanic event can have a range of impacts, affecting the area immediately around the volcano. Volcanic effects become a hazard when they impacts upon human and built environments, killing and injuring people and destroying infrastructure. Hazards can be categorised into primary and secondary. Primary hazards consist of features from the initial explosion such as pyroclastic flows, lava, volcanic gases and ash. Secondary hazards are less directs ones and include lahars, flooding and tsunamis. The factors that cause differences in the hazards posed by volcanoes include the type of plate margin, the rock type and to an extent the management of a volcano.  

Constructive plate margins are where two plate margins move apart and the space between the diverging plates is filled with basaltic lava upwelling from below. Oceanic ridges are the longest continuous uplifted features on the surface of the planet and have a total length of around 60,000 km. Volcanic activity occurs along the ridge, forming submarine volcanoes which sometimes rise above sea level. The general trend is that volcanic eruptions at constructive plate margins are not very hazardous. This is due to the type of lava that is common at constructive plate margins. When the Basaltic magma is forced to the surface, only a small amount of the mass actually reaches that level. Most of the magma is intruded into the crust where is solidifies into a range of features including the lithosphere. Basaltic lava has a low viscosity which means it is very runny like warm treacle. This type of lava is not threatening as shown in Hawaii where in fact it attracts tourists to view the fascinating spews of lava. The form of the volcano at a constructive plate margin tends to be a shield volcano also known as a lava plateau. They are gently sloping because the lava takes a long time to solidify so flows considerable distances as it retains its gas content which make the lava mobile. Overall, the general pattern is that due to the mantle being ultra-basic, eruptions at constructive plate margins despite being frequent and sometimes continuous possess little violence and are relatively gentle.