Both volcanoes and earthquakes are caused by the movement of magma beneath the earths crust. The crust can be between six and seventy kilometres thick, this can be symbolised by the skin of an apple. The crust is both on land and under sea’s, however the composition of the crust changes. Oceanic crust is denser and usually composes of silicon and magnesium; where as continental crust is lighter and usually composes of silicon and aluminium. Beneath the Mohorovicic discontinuity the convection currents of the liquid mantle control the movement of the tectonic plates, causing both volcanoes and earthquakes. The convection currents vary in size and can be anywhere in between 800 and 1200 miles across. These convection currents move the huge tectonic plates, the boundary’s of these plates are called fault lines and are the areas in which both volcanoes and earthquakes occur. Both hazards have many implications on both the human population and the environment, the purpose of this essay is to discuss which hazard has the more dangerous implications.
A volcano is a vent in the earths crust from which hot gasses, pyroklastics, and lava can be emitted, there are two types of activity from volcanoes extrusive and intrusive. There are two types of extrusive activity, volcanic plateaus and localised volcanic mountains, Intrusive activity is described as sills and dykes. The type of activity obviously determines danger of the volcano. Extrusive volcanic mountains are by far the most dangerous volcanic hazard as they can emit all 3 volcanic materials and can also cause secondary hazards such as lahars, mudslides and widespread flooding (only if the mountain is covered by a glacier) An example of an extrusive volcano is Nevado del Ruiz in Columbia, 22,000 died in the town of Armero due to lahars caused by the melting of a glacier. Volcanoes are capable of being predicted, if accurate prediction is linked with a towns authority it can save thousands of lives.
There are two main ways both are in use at present on active volcanoes around the world. Sulphur dioxide concentrations can be measured in gas emissions; this indicates the presence of magma moving up through the cracks in the rocks. Seismographs can also be used, different patterns in the graph, called A and B waves, A waves can indicate the cracking of rock. B waves can be used to detect resonance within the rock indicating movement of magma, this concept was theorised by Dr Bernard Chouet. Volcanoes are hard to protect against showing the devastating nature of the materials expelled from volcanoes, lava when fresh burns at 1200ï¿½C and can move from 4 to 40 mph. two methods that are used are water sprays and explosives, during the 1973 eruptions at Eldafell on Haeimaey in Iceland water sprays were used to successfully cool lava flows and protect the harbour in Vestmannaeybar. However the US air force has bombed craters to try and divert lava flows, this failed miserably.
Earthquakes are caused by the friction between plate boundaries, when plates either slide past each other or collide. There are around 1 million earthquakes a year of those 1000 are felt and 100 cause damage. Earthquakes are measured by two scales, the Richter and the Mercalli scales. An earthquake causes three waves, P, S and L. An example of an earthquakes power is the 1995 quake that occurred in Kobe in Japan, over 5000 people died, over 30,000 were injured, and 750,000 were made homeless.
Earthquakes are more difficult than volcanoes to predict, techniques used are, animal behaviour, minor quakes, crustal movement and gas omissions. These techniques don’t provide an accurate warning; showing the unpredictable and dangerous nature of earthquakes. A method of long term protection is usually adopted; shock absorbers and specialist foundations have shown good success rates. However some protections have been shown to completely fail, a specially built highway in Japan was meant to withstand earthquakes instead it collapsed crushing hundreds of motorists.
Both hazards are deadly and ruin both property and human life; however volcanoes in my opinion are more dangerous than earthquakes. Earthquakes although cannot be predicted can be protected against saving thousands of lives. Volcanoes although can be predicted cannot be defended against, even if towns are evacuated they are still destroyed creating huge humanitarian and economic problems. Accurate volcano prediction if in place isn’t always linked up with towns in danger; this makes the prediction useless anyway. Finally Volcanoes also have lasting implications; their secondary effects such as lahars can be felt for generations.