This part of the book invites the reader to look closer at plate tectonics and volcanism, and then draw inspiration from geological events, processes, and products for creating a visual and/or verbal project. The next part is about earthquakes, tsunami, the explosive eruptions of volcanoes such as Mt. St. Helens, Yellowstone, and Vesuvius, about the Japan 2011 earthquake, and the impact of volcanism on human fates.
TopPlate Tectonics And Volcanoes
A volcano is a break in a planet's crust, which frees out a hot magma, volcanic ash, and gases, so they burst and escape from below the surface. Magma contained within crust or mantle rise and form volcanic rocks on the surface. Volcanoes are generally found where tectonic plates are parting or converging. The surface of the Earth is composed of the crust and upper mantle (called together the lithosphere). According to the scientific theory about plate tectonics, a large-scale process called tectonics resulted in broking the lithosphere into 14 large and 38 small tectonic plates (Bird, 2003). The plates (with areas and shapes different than the continents or oceans) move up to 100 mm per year above a hot, more mobile, underlying asthenosphere. Digital models of the plate boundaries have been computed, based on the literature sources (e.g., Bird, 2003).
The Earth’s interior is divided into layers, which differ in their chemical composition and physical properties. The crust is the farthest from the center layer of the Earth. The oceanic crust in the region of Hawaii is about 5 kilometers thick, while the continental crust under eastern California is from about 30 km thick (Robertson, 2011). The mantle is a layer between the crust and the outer core. It forms a rocky shell about 2,900 km (1,820 miles) thick (Schlumberger, 2012), which makes about 84% of Earth's volume (Robertson, 2011). Continental crust comprises rocks of the granite and basalt types, while oceanic crust is basaltic. In deeper layers it has a thick, sticky consistency between solid and liquid. Between the crust and the mantle, the Mohorovicic discontinuity, called Moho, separates crust from the mantle and marks a sharp increase of the speed of earthquake waves, possibly due to the change in rock types (Robertson, 2012).
Scientists work on advancing the science of forecasting a volcanic eruption. They are able to detect the buildup preceding a catastrophic eruption for weeks, months, or even years. Earthquakes and ground deformations are the precursors of imminent volcanic eruptions; typically they take place days to weeks before an actual eruption. However, scientists cannot do anything to prevent or control eruptions because of the immensity of the temperature, pressure, physical characteristics of partially molten rock, and the extent of the magma chambers.
Figure 1 presents two student works about magma. For directions on depicting plate tectonics and volcanoes, see Table 1.
Figure 1. Left: Mathew Skiff, “Earth,” Right: Nathan White, “Core”(© 2006, M. Skiff and N. White. Used with permission)