We know why igneousactivity is initiated along plate boundaries, but why do eruptions occur in the interiors of plates? Hawaii's Kilauea is considered the world's most active volcano, yetitis sit uated thousands of kilometers from the nearest plate boundary in me the middle of the vast Pacific plate(Figure 9.36C). Other sites of intraplate volcanism(meaning"within the plate) include the e Canary Islands, Yellowstone, and several volcanic centers that ed you may be surprised to learn are located in the Sahara Desert of Africa. Geologists now recognize that most intraplate volcanism of occurs where a mass of hotter than normal mantle material called l a mantle plume ascends toward the surface(Figure 9.360) in Although the depth at which(atleast some) mantle plumes orig n- inate is still hotly debated, some appear to form deep within Earth at the core-mantle boundary. These plumes of solid yet nt mobile mantle rock rise toward the surface in a manner similar to to the blobs that form within a lava lamp. (These are the lamps that contain two non-mixing liquids in a glass container. As the million base of the lamp is heated, the denser liquid at the bottom slowly becomes buoyant and forms blobs that rise to the top,) Like the flood b blobs in a lava lamp, a mantle plume has a bulbous head that to the H draws out a narrow stalk beneath it as it rises. Once the plume markin head nears the top of the mantle, decompression melting gen(Figure erates basaltic magma that may eventually trigger volcanism at the surface. The resultis a localized volcanic region a few hundred kilo meters across called a hot spot(Figure 9.36C). More than 40 hot spots have been identified, and most have persisted for millions CON 0 Are of years. The land surface surrounding a hot spot is often ele vated because is buoyed up by the rising plume of warm low density material. Furthermore, by measuring the heat flow in G Ho these regions, geologists have determined that the mantle bo beneath hotspots must be 100-1500 Chotterthan normal man Vo tle material. Mantle plumes are responsible for the vast outpourings of basaltic lava that created the large basalt plateaus including O WI the Siberian Traps in Russia, India's Deccan Plateau, and the o At Ontong Java Plateau in the western Pacific. The most widely accepted explanation for these eruptions, which emit extre mely large volumes of basaltic lava over relatively short time intervals, involves a plume with a monstrous head and along narrow tail(Figure 9.3A). Upon reaching the base ofthe lithos- phere, these unusually hot, massive heads begin to melt. Melt Liv ing progresses rapidly, causing the burst of volcanism that emits voluminous outpourings of lava to form a huge basalt plateau Abou in a matter of a million or so years(Figure 9.37B). The com- an ac paratively short initial eruptive phase is followed by tens of millions of years of less voluminous activity, as the plume tai slowly rises to the surface. Extending away from most larg flood basalt provinces is a chain of volcanic structures, simila to the Hawaiian chain, that terminates over an active hot spot marking the current position of the remaining tail of the plume(Figure 9.37C)