Plate Tectonics, Earthquakes, & Volcanoes Chapters 7, 8, & 9

Structure of the Earth Lithosphere: crust and upper part of mantle Asthenosphere: plastic-like part of mantle where convection currents are found Mesosphere: lower part of mantle Outer core: liquid iron and nickel Inner core: solid iron and nickel

Plate Tectonics Plates can be made of oceanic or continental crust, and sometimes both Three types of plate movement due to different stresses/forces are convergence (compression), divergence (tension), and transform (shear) Convergence is also sometimes known as subduction, where one dense plate is pulled underneath a less dense plate Depending on the type of plate, convergence can create island arcs, mountains, or trenches Divergence creates mid-ocean ridges and rift valleys Transform boundaries are usually identified by strike-slip faults, like the San Andreas Fault in California

Plate Movement

Earthquakes & Faults Faults are cracks in the Earth’s crust where plate movement occurs Movement can be due to tension (normal fault), compression (reverse fault), or shearing (strike-slip fault)

Where Do Earthquakes Happen? Wherever there is stress that builds up in the Earth, it gets released at the focus The energy that is released is done so through primary (compressional), secondary (shearing), and surface waves

Volcanoes Volcanoes are typically found where plates are colliding and pulling apart. Volcanism is NEVER found at transform boundaries. Hot spot volcanism occurs in the middle of tectonic plates. Examples would be Hawaii and Old Faithful in Yellowstone National Park. Violent eruptions occur at subduction zones, like around the Pacific Ring of Fire. Usually composite and cinder cone volcanoes are found here. Mt. St. Helens is an example. Quiet eruptions are characteristic of shield volcanoes, like Kilauea in Hawaii.

Geologic Provinces of VA A physiographic province is a landform region, an area delineated according to similar terrain that has been shaped by a common geologic history. Each province is characterized overall by its elevation, relief, lithology, and geologic structure.

Geologic Provinces, cont’d Appalachian Plateau: Although some parts of the plateau are relatively flat, there are many valleys and stream hollows, making it much of the Appalachian Plateau very hilly and rugged. The upper Paleozoic layers of the plateau are rich in mineral resources like coal, natural gas, and petroleum. Valley and Ridge: made up of long parallel ridges and valleys with folded Paleozoic sedimentary rock below and inside them. Cambrian-aged sandstones (540 million years-old) from the western Blue Ridge are overlain by carbonates that made up a big region of limestone and dolomite called the Great American Carbonate Bank. Today these carbonates (up to 3.5 kilometers in thickness) are exposed in the Great Valley, the easternmost portion of the Valley & Ridge province. Well-developed caves and sinkholes can be found in the Great Valley. Blue Ridge: In Virginia, the oldest rocks in the Blue Ridge province are different types of granite which date back 1,200,000,000 years. The rocks that make up the Blue Ridge have been shoved over the rock layers of the Valley & Ridge province. The rocks were moved to the northwest when Africa and North America got sandwiched together, pushing the Blue Ridge on top of the Valley & Ridge along a fault line. By being deformed, older igneous and metamorphic rocks show that the continents crunched together and split apart many times during the Paleozoic. Piedmont: is the largest physiographic province in Virginia. It is bounded on the east by the Fall Zone, which separates the province from the Coastal Plain, and on the west by the mountains of the Blue Ridge province. A variety of igneous and metamorphic rocks make up the bedrock of the Piedmont province. Coastal Plain: extends from the Fall Zone eastward to the Atlantic Ocean. Through the Fall Zone, the larger streams cascade off the resistant igneous and metamorphic rocks of the Piedmont to sea level. The topography of the Coastal Plain is a terraced landscape that stair-steps down to the coast and to the major rivers.