Plate Tectonics Plate: large rock surfaces along which rocks can break or move Plate Tectonics: Primary process that creates earthquakes and volcanoes and determines the geography of Earth’s surface The USA is almost completely on the North American Plate As mentioned earlier, plates are large slabs of rock among the lithospheric crust that can break or move. There are about 15 major tectonic plates on Earth’s surface that influence Earth’s climate and life’s evolution as they move. Plate tectonics shape Earth’s geography and may cause natural disasters in the process.

Plate Tectonics Visual representation to help understand the previously introduced terms.

Three Types Plate Tectonics Divergent plate boundaries Transform plate boundaries Convergent plate boundaries Brief preview slide of what’s coming on for the next few slides.

Divergent Plate Boundaries Magma rises from under the crust. Two plates divide and are steadily pushed apart. New crust is created. Ex. Mid-Atlantic Ridge At divergent plate boundaries, magma rises from beneath the crust, surging to the surface and dividing plates by pushing them apart. New crust is created as the magma cools and spread. This normally causes mid-ocean ridges like the Mid-Atlantic Ridge while creating new plate boundaries with the new plates.

Transform Plate Boundaries Two plates slide next to each other. They create friction that leads to earthquakes along strike-slip faults Strike-slip Fault: an extended crack in the crust that breaks down the rocks on either side. At transform plate boundaries, two plates slide parallel to each other and create friction along faults. This normally generates earthquakes like the San Andreas Fault in California. Strike-slip faults are vertical fractures where the blocks have moved mostly horizontal. Ex. Pacific Plate and North American Plate → San Andreas Fault, making California a place with many earthquake.

Convergent Plate Boundaries Plates collide together causing one plate to slide beneath another in subduction, causing magma to emerge in volcanoes both plates to lift, creating new mountain ranges Ex. Mt. Saint Helens of the Cascades. At convergent plate boundaries, two plates collide against each other causing one of two things to happen. One, a plate can slide beneath another in the process called subduction, heating up the subducted crust so that magma erupts through volcanoes as it had in Mount Saint Helens in 2004. When an oceanic crust is subducted beneath another, the volcanoes can create new arcs of islands for Japan or deep trenches like Mariana Trench. Two, both plates can be uplifted into mountain ranges as they had for the creation of the Himalayas and Appalachian Mountains. Ex. Himalayas and Appalachian Mountains