Presentation on theme: "Warm Up 11/26 The Hawaiian Islands were formed when the Pacific Plate moved over ____. a. a hot spot c. the Aleutian Plate b. a subduction zone d."— Presentation transcript:
1Warm Up 11/26The Hawaiian Islands were formed when the Pacific Plate moved over ____.a. a hot spot c. the Aleutian Plateb. a subduction zone d. an ocean ridgeStrips of alternating magnetic polarities found in rocks in the ocean basins ____.a. conflict with the theory of plate tectonicsb. provide evidence that Earth’s magnetic field has never reversed polarityc. indicate changes in Earth’s gravitation fieldd. provide evidence for seafloor spreadingThe formation of the Hawaiian Islands is associated with ____.a. a convergent plate boundary c. a transform fault boundaryb. a divergent plate boundary d. no plate boundary of any kindAnswers: 1) a. 2) d. 3) d.
3Causes of Plate MotionScientists generally agree that convection occurring in the mantle is the basic driving force for plate tectonicsConvective Flow – the motion of matter resulting from convectionThe slow movements of the plates and mantle are driven by the unequal distribution of Earth’s heat from the radioactive decay elements
5Slab-Pull and Ridge-Push Slab-Pull – old oceanic crust, which is relatively cool and dense, sinks into the asthenosphere and “pulls” the trailing lithosphere alongSlab-pull is thought to be the primary downward arm of convective flow in the mantleRidge-Push – causes oceanic lithosphere to slide down the sides of the oceanic ridge as a result of gravity
6Mantle ConvectionMantle Plumes – hot plumes of rock that are attributed to the upward flowing arms of mantle convectionMantle plumes sometimes show themselves on the surface as hot spots and volcanoesWhole-mantle convection is when slabs of cold oceanic lithosphere descend into the lower mantle, at the same time, hot mantle plumes originating near the mantle-core boundary move heat toward the surfaceAnother model is called the deep-layer model , and can be likened to a lava lamp, heat from Earth’s interior causes the layers to mix and combine in swirling patternsThe unequal distribution of heat within Earth causes the thermal convection in the mantle that ultimately drives plate motion