Since the degree of impact an earthquake has is measure on both the Richter and the Mercalli scale, it must be reasonable to assume that the power of an eruption is representative to the degree of how potentially hazardous the event may be. Eruption explosiveness can be measured by the Volcanic Explosivity Index. The higher the Volcanic Explosivity Index, the greater the potential hazard. The eruption type is a huge factor in the differences in the degree of hazards posed by volcanoes around the world. This greatly relates to the plate margin the volcano or volcanic belt is situated upon.
NOVA: Volcanoes Volcanoes are landforms where molten rock erupts through the surface of the planet. Think of them as pimples on the face of the earth. Today, there are over 1,500 active volcanoes on earth’s surface. Volcanoes cause serious hazards to not only people, but the environment and the nature around us as well. If an eruption were to occur, a number of life-changing things would happen.
One hazard can often trigger others (e.g. Earthquakes can cause landslides and tsunamis). The San Andreas Fault is a conservative plate boundary that runs 1300km along the Californian coastline. The fracture within the crust, causes crustal instability, between the North American and the Pacific plate. As it traverses, due to convection currents, the tectonic plates are dragged along the entire length of the Californian coast.
This knowledge of plate margins and their movement against one another can help us to understand the distribution of seismic and volcanic events and this is because the majority of events are associated at these plate margins. Wegener’s theory of plate tectonics suggests that all the continents were once joined together in a super continent called Pangea and have since drifted apart due to plate tectonics. To add to this, Sea floor spreading was discovered showing that rock is being created and destroyed, leading us to believe in the existence of plates and plate boundaries. Wegener gained evidence from paleo magnetism and suggested that there were numerous reasons and pieces of evidence for the continents drifting apart. Biologically, there was evidence that proved his theory for example, the Mesosaurus reptile fossils were only found in Africa and South America, proving his ‘jig-saw’ fit idea.
However despite this, as 95% of earthquakes occur on plate boundaries there must be some kind of link between the two and plate tectonic theory can explain this. The theory suggests that the earth’s crust is split into plates which are huge slabs of rock that move due to the convection currents in the mantle. Where two plates meet it causes friction along the plate margin and this creates stresses in the lithosphere and tension in the rock builds overtime. When the strength of the rocks under stress suddenly breaks, they fracture along cracks called faults, sending a series of seismic
The nature of an event is initially determined by how the cause was stimulated. Volcanic eruptions occur in many different forms determined by the plate margin they are on. The eruptions on Montserrat 1995 show a strong example of the nature of a volcano at a destructive plate margin. The Soufriere Hills volcano had lay dormant for a long period of time. When the eruption did occur it was seen as explosive as it produced large volumes of acidic lava, ash, pyroclastic flows and steam.
Lava and pyroclastic flows are both examples of primary volcanic hazards, whilst lahars landslides are secondary. Seismic hazards are initially ground movement and landslides, and in some cases can be preceded by tsunamis. The soonest discovery made after Wegner’s proposal was Harry Hess’ finding of a concept known as Sea Floor Spreading in 1950. This occurs mainly at constructive plate margins in which magma rises through the newly created space caused by the spreading
In which ways does volcanic activity vary in relation to the type of plate margin along which it occurs? (10 Marks) Volcanic activity can occur at constructive or destructive plate margins, but it can also occur at hotspots in which no plate margin is involved. At destructive margins two plates which are moving together can be either both oceanic plates or one continental and the other oceanic. In the case of one continental plate and one oceanic plate, volcanic eruptions are very violent and emit andesitic or rhyolitic lava. These types of lava are very viscous due to its high silica content.
To what extent can preparedness and planning mitigate the effects of volcanic hazards? (40 Marks) A volcanic hazard is any threat to life and infrastructure due to volcanic activity and related situations such as a landslide near the volcano. There are many different types of volcanic hazard and each can have different impacts on the economy, society and environment in a region. It is extremely important that disaster reduction measures, such as early warning systems and land use planning, are implemented to try to reduce these impacts. There are three main stages to consider when managing a volcano: before the eruption, during its critical period and evacuation.
Discuss the Extent to which Tectonic hazards can be Monitored 40 marks Monitoring tectonic hazards involves being able to predict when they will occur and the extent of the damage they may cause and in this way we can prevent maximum harm taking place. When predicting volcanoes it’s important to look at their history of previous eruptions and the type of volcano. The most recent research was in time prediction using shock waves that are produces as magma reaches the surface which expands cracks or breaks the surface of the volcanic rock. This was partly successful in a Mexican eruption in 2002 of Popacatapelt. Using the history of eruptions allows us to assess what is likely to happen in the future, for example, in the eruption of Mt.