Download
1 / 50
510 likes | 667 Vues
Plate Tectonics. In this lesson you will: 1.1.3 Relate selected plate movements to compressional and tensional forces. Plate Tectonics. Mountain Ranges . Tend to coincide with subduction zones at the boundaries between two converging plates.
E N D
Plate Tectonics • In this lesson you will: • 1.1.3 Relate selected plate movements to compressional and tensional forces.
Mountain Ranges • Tend to coincide with subduction zones at the boundaries between two converging plates. • The tremendous compressional forces literally fold the thin crust in to mountains. • Remember this occurs over millions of years.
Volcanoes • Can occur at subduction zones or at ridge zones. • At subduction zones the compressional forces sometimes leave a crack in the crust that allows the magma to reach the surface. • At ridge zones the plates are moving apart which allows magma to reach the surface from the asthenosphere. • Because of the excessive number of active volcanoes on the coast around the pacific ocean it is known as the Pacific Ring of Fire.
Earthquakes • Often occur at transform zones where the plates are moving beside each other instead of toward or away from each other. • Notice that subduction zones occur where the tectonic plates are moving towards each other • While Ridge zones occur where the plates are moving apart and transform zones occur where plates are moving side by side.
Folded Mountains • In this lesson you will: • 1.1.4 Explain how compressional forces create fold mountains. (k) • 1.1.5 Differentiate between the terms anticline and syncline.
How are fold mountains formed? • Most Major Mountain ranges were formed by folding. • Fold mountains are formed when two continental plates move towards each other or a continental plate moves towards an oceanic plate. • The movement of the two plates forces sedimentary rocks into a series of folds
Fold mountains are usually formed from sedimentary rocks and are usually found along the edges of the continents. • When plates collide, the accumulated layers of rock crumple and form a series of fold mountains. • There are two types of fold mountains: • young fold mountains ( 10 to 25 million years of age, e.g. Rockies and Himalayas ) • old fold mountains (over 200 million years of age, e.g. Urals and Appalachians of the USA)
Folding • Folding is a process in which the Earth's plates are pushed together in a roller coaster like series of high points and low points. • Folding bends many layers of rocks without breaking them. • The peaks are known as anticlines • The valleys are known as synclines.
Tectonic Faults • In this lesson you will: • 1.1.6 Explain how tensional forces create a normal fault. (k) • 1.1.7 Explain how compressional forces create reverse and overthrust faults. (k)
Tectonic Faults • Fault lines are great cracks in the crust. Types of Faults: 1. Mountains Formed by Normal Faults 2. Mountains Formed by Reverse Faults 3. Fault Block Mountains 4. Overthrust Faults
Mountains Formed by Normal Faults • Normal Faults are caused by tensional forces. When the land moves apart at a fault line one plate drops down lower than the other. • See Diagram
If you stood on the fault plane, the block on the right would be under your feet. This is thus the footwall.The red line marks equivalent layers on opposite side of the fault. Since the hanging wall dropped relative to the footwall, this is clearly a normal fault.
Mountains Formed by Reverse Faults • Reverse faults are caused by compressional forces where plates move together at the fault. The land that rises above can form a mountain. • See Diagram
Reverse faults are caused by compresional stresses, and are often found at convergent plate boundaries
Fault Block Mountains • Sometimes form when many layers of the Earth's crust are moved vertically upward between two parallel fault lines. Vertical force is caused by the earth's internal pressure. The mountains that are formed in this way are called fault-block mountains. • The Sierra Nevada mountains in California and Nevada, and the Grand Teton range of Wyoming are examples of fault-block mountains. • See Diagram
Over-thrust Faults • Over-thrust Faults are caused by compressional forces where plates move together at the fault. • They are a class of reverse faults that have had folding occur before the fault formed. • See Diagram
Volcanic Mountains • In this lesson you will: • 1.1.8 Explain what causes a volcano to erupt. (k) • 1.1.9 Describe the characteristics of an ash and-cinder cone, a shield cone, and a composite cone. (k) • 1.1.10 Conclude how the location of active volcanoes is related to places where plates meet. (a)
Volcanic Mountains • Volcano is an opening in the earth's crust through which magma, gasses, and ash erupt. • The shape of the volcano depends on the thickness of lava. • Most volcanoes occur on plate boundaries.
Three Types of Volcanoes • Ash and Cindervolcanoes • Shieldvolcanoes • Composite volcanoes
Ash and Cinder Volcanoes • The simplest type of volcano. • They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone.
Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. • Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world. • They are very explosive because the lava is very thick and slow flowing. It blocks the vent causing pressure to build up to high levels before it finally blows.
Shield Volcanoes • Built almost entirely of fluid lava flows. • Flow after flow pours out in all directions from a central summit vent, or group of vents, building a broad, gently sloping cone of flat, domical shape, with a profile much like that of a warrior's shield.
They are built up slowly by the accretion of thousands of highly fluid lava flows called basalt lava that spread widely over great distances, and then cool as thin, gently dipping sheets. • These are the least explosive because the lava is so thin and fluid that it does not block the vent and prevents pressure build up.
Composite Volcanoes • Have a conduit system through which magma, from a reservoir deep in the earth's crust, rises to the surface. • The volcano is built up by the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash, etc., are added to its slopes. • The lava varies causing it to be explosive one time while the next time it can be gentle flowing.
Great web site • http://www.nationalgeographic.com/forcesofnature/
