Plate tectonics, tsunamis, volcanoes, and seasons

1. Plate tectonics, tsunamis, volcanoes, and seasons By Ginny Bister

2. Earth structure • Earth can be divided into 3 sections: the biosphere, the hydrosphere, and the internal structure • Biosphere: includes all forms of life • Hydrosphere: includes all forms of water • Internal structure: includes crust, mantle, and core

3. Plate tectonics • Theory rose from two separate geological observations: continental drift and seafloor spreading • Continental drift theory • Alfred Wegener proposed that all present day continents were once one landmass (Pangaea) • theory was based on 5 factors • Fossilized plants discovered beneath Greenland's ice caps • There were glaciers in africa and south America • The continents fit together like a puzzle • Similarities existed in rocks on the east costs of the Americas and on the west coasts of africa and Europe • Present day tropical regions once had polar climates • Seafloor spreading theory • During the 1960’s alternating patterns of magnetic properties were discovered in rocks on the seafloor as well as mid-oceanic ridges • Dating of the rocks suggests that as a rock moved away from the ridge, it got older • This suggested that new crust was being created at volcanic rift zones

4. Plate tectonics (cont.) • Transform boundaries • Plates slide past each other • The friction and stress buildup causes earthquakes • Convergent boundaries • When two plates slide toward each other • Can form a subduction zone or an autogenic belt (of two plates collide and compress) • Divergent boundaries • When two plates slide apart from each other • The space created is filled with magma • Can create massive fault zone in the oceanic ridge system

5. Earthquakes • Caused by friction from transform boundary plates • Severity of an earthquake depends on • The amount of stored potential energy • The distance the rock mass moved when the energy was released • How far below the surface the movement occurred • The makeup of the rock material

6. Volcanoes and tsunamis Tsunamis Volcanoes A series of waves created when a body of water is rapidly displaced by an earthquake Can be generated when plate boundaries abruptly move and vertically displace the overhead water Small wave heights offshore and long wavelengths and generally pass unnoticed out at sea Mainly generated in the pacific and Indian oceans Active volcanoes produce magma at the surface Other volcanoes are classified as intermittent, dormant, or extinct The majority occur at subduction zones and mid-Atlantic ridges and the remainder occur at hotspots The most common gases formed by volcanoes are steam, carbon dioxide, sulfur dioxide, and hydrogen chloride

7. Seasons • Seasons are affected by the amount of solar energy on the earths surface, earths rotation, earths revolution, and the tilt of earths axis • Summer occurs for the northern hemisphere when it is pointed toward the sun, which results in longer daylight hours • Vise versa in the winter • Actually in the winter the northern hemisphere is closer to the sun

8. Review questions What are the three sections of the earth and what do they include? What accounts for the severity of an earthquake? How is a tsunami created? What are the main gases released by a volcanic eruption? What are all the factors of seasons?

9. Links Seasons: http://nitrogencycle.weebly.com/index.html plate tectonics, volcanoes, and earthquakes: http://www.eoearth.org/article/AP_Environmental_Science_Chapter_3-_The_Solid_Earth Tsunamis: http://www.tsunami.noaa.gov/

10. Videos Plate tectonics: http://www.youtube.com/watch?v=hqp_TbIZU64 Volcanoes earthquakes, and tsunamis: http://www.youtube.com/watch?v=XSUCRiKIql8