Individual work

Task 1. Read the text and translate it into Ukrainian (in written form). Build up a list of key terms to the text. While reading have a look at Figure 8.3: A, B and C. The figure shows the model of hot-spot volcanism thought to explain the formation of oceanic plateaus and the volcanic islands associated with these features. A. A rising mantle plume with large bulbous head and narrow tail. B. Rapid decompression melting of the head of a mantle plume produces vast outpourings of basalt to generate the oceanic plateau. Large basaltic plateaus can also form on continental crust—examples include the Columbia Plateau in the north-western United States and India’s Deccan Plateau. C. Later, less voluminous activity caused by the rising plume tail produces a linear volcanic chain on the seafloor.

Most intraplate volcanism (meaning “within the plate”) occurs where a mass of hotter than normal mantle material called a mantle plume ascends toward the surface. Although the depth at which mantle plumes originate is still hotly debated, some appear to form deep within Earth at the core–mantle boundary. These plumes of solid yet mobile mantle rock rise toward the surface in a manner similar to the blobs that form within a lava lamp. Like the blobs in a lava lamp, a mantle plume has a bulbous head that draws out a narrow stalk beneath it as it rises. Once the plume head nears the top of the mantle, decompression melting generates basaltic magma that may eventually trigger volcanism at the surface.

The result is a localized volcanic region a few hundred km across called a hot spot. More than 40 hot spots have been identified, and most have persisted for millions of years. The land surface surrounding a hot spot is often elevated because it is buoyed up by the rising plume of warm low-density material. By measuring the heat flow in these regions, geologists have determined that the mantle beneath hot spots must be 100 to 150 °C hotter than normal mantle material.

Mantle plumes are responsible for the vast outpourings of basaltic lava that created the large basalt plateaus including the India’s Deccan Plateau, and the Ontong Java Plateau in the western Pacific. The most widely accepted explanation for these eruptions, which emit extremely large volumes of basaltic lava over relatively short time intervals, involves a plume with a monsterous head and a long, narrow tail (FIGURE 8.2, A). Upon reaching the base of the lithosphere, these unusually hot, massive heads begin to melt. Melting progresses rapidly, causing the burst of volcanism that emits voluminous outpourings of lava to form a huge basalt plateau in a matter of a million or so years (FIGURE 8.2, B). The comparatively short initial eruptive phase is followed by tens of millions of years of less voluminous activity, as the plume tail slowly rises to the surface. Extending away from most large flood basalt provinces is a chain of volcanic structures, similar to the Hawaiian chain that terminates over an active hot spot marking the current position of the remaining tail of the plume (FIGURE 8.2, C).

Task 2. Answer the questions (in written form):

1. What is the source of magma for intraplate volcanism?

2. At which type of plate boundary is the greatest quantity of magma generated?

Task 3. Look at Figure 8.2, C and D. What is the difference between intraplate oceanic volcanism and intraplate continental volcanism? Answer the question in written form.

Task 4. Look at Figure 8.4. This is a simplified drawing showing a wide variety of natural hazards associated with volcanoes. Make a short report about the hazards.