Plate Tectonics and People
In Chapter 4 you have learned how plate tectonics is a comprehensive and unifying theory that is central to the study of geology. This system of moving plates is not only responsible for driving the rock cycle, but it also creates the major surface features of our planet. However, the importance of plate tectonics goes far beyond geology. Because Earth acts as a system, namely the atmosphere, hydrosphere, and biosphere. In this final section we will briefly touch on some of the ways in which plate tectonics affects the lives of humans and modern societies. This is quite appropriate since the focus of this textbook is on the interaction between environmental geology and people.
Natural Hazards
There are many geologic processes that create natural hazards for humans and society. In this text we will focus on the hazards that are associated with earthquakes, volcanic eruptions, and the downslope movement of earth materials (i.e., landslides), all of which are clearly related to plate tectonics. As you have learned thus far in this chapter, the majority of earthquakes and volcanic eruptions occur along plate boundaries as does the uplift of mountain ranges, which generates steep slopes and the potential for landslides. Therefore, the level of risk people face from these hazards greatly depends on where they live relative to Earth’s plate boundaries.
If we consider just earthquakes and volcanic eruptions, we will find that the relative risk from the hazards varies according to the type of plate boundary, as indicated in Table 4.2. Earthquakes, for example, can happen far from a plate boundary, but most occur along plate boundaries where rocks are subjected to tremendous amounts of stress. However, the amount of energy released in an earthquake is directly related to the amount of stress rocks can store before rupturing when they reach their elastic limit. Because rocks can store a great deal more energy when under compression or shear forces than tension, major quakes are much more common along convergent and transform boundaries (Table 4.2). Volcanic hazards, on other hand, exist only in areas where rocks deep in the subsurface are able to melt and form magma. The generation of magma then is largely restricted to divergent boundaries and those convergent boundaries involving subduction. The reason volcanic hazards are ranked higher along convergent settings in Table 4.2 is because subduction zones typically generate magmas that cause more explosive and violent eruptions