GEOG101 Chapt03 lecture
Download as PPT, PDF1 like1,435 views
This document provides an overview of earth materials, geologic time, movements of the continents, tectonic forces, and gradational and erosional processes that shape landforms and landform regions. It describes the three main types of rocks - igneous, sedimentary, and metamorphic - and how they are formed. It also explains plate tectonics theory and how the movement of tectonic plates results in diverse landforms and geological phenomena like earthquakes and volcanoes globally.
GEOG101 Chapt03 lecture
- 1. Overview Earth Materials Geologic Time Movements of the Continents Tectonic Forces Gradational Processes Landform Regions
- 2. Earth Materials Igneous Rocks Sedimentary Rocks Metamorphic Rocks
- 3. Igneous Rocks Formed by the cooling and solidification of molten rock Magma: molten rock below ground Cooling forms intrusive igneous rocks Granite Lava: molten rock above ground Cooling forms extrusive igneous rocks Basalt, pumice, obsidian Composition of magma and lava plus cooling rate determines the minerals that form
- 4. Sedimentary Rocks Composed of eroded particles of gravel, sand, silt, and clay Rocks evolve in horizontal strata Compressed by weight of additional deposits and cemented by water and certain minerals Type of sediment determines rock type Large, rounded particles form conglomerates Sand forms sandstone Silt and clay form shale or siltstone Organic materials form limestone or coal
- 5. Metamorphic Rocks Formed from igneous or sedimentary rocks by earth forces that produce heat, pressure, or chemical reactions Mineral structure is changed Shale becomes slate Limestone may become marble Granite may become gneiss
- 6. Geologic Time Earth formed about 4.7 billion years ago Theory of continental drift Based on early 20 th -century work of Alfred Wegener All land masses were once united in a supercontinent; continents drifted apart over many millions of years Pangaea: “all Earth” Forerunner of plate tectonics theory
- 7. Movements of the Continents Plate tectonics theory Asthenosphere Partially molten layer above the core and lower mantle Lithosphere Outermost layer of the earth (the crust and upper mantle) 12 large and numerous small plates that slide or drift slowly over the asthenosphere May be due to convection of molten material in asthenosphere
- 8. Movements of the Continents Divergent plate boundaries Plates move away from each other Transform boundaries One plate slides horizontally past another Convergent boundaries Plates move toward each other Subduction may occur One plate is forced beneath another Earthquakes and volcanic activity may occur in the vicinity of plate boundaries Ring of Fire
- 9. Tectonic Forces Diastrophism Earth force that folds, faults, twists, compresses rock Volcanism Earth force that transports subsurface materials to or toward the surface of the earth
- 10. Diastrophism Broad warping Bowing of a large region of the earth’s surface Folding Layers of rock are forced to buckle Faulting Rock is broken or fractured Escarpments, rift valleys Earthquake Movement along a fault or point of weakness Tsunami Sea waves generated by an earthquake, volcanic eruption, or underwater landslide
- 11. Volcanism Usually at or near plate intersections Also at hot spots Strato or composite volcano Explosive, steep sides Shield volcano Non-explosive, gently sloping Magma may not reach the surface Lava may flow through fissures or fractures without forming a volcano
- 12. Gradational Processes Reduction of the land’s surface Weathering Mass movement Erosion
- 13. Weathering Processes that fragment and decompose rock Mechanical Physical disintegration Frost action Salt crystals Root action Chemical Decomposition as a result of chemical reactions Oxidation Hydrolysis Carbonation
- 14. Mass Movement Downslope movement of material due to gravity Avalanches Landslides Soil creep Talus Landform created by the accumulation of rock particles at the base of hills and mountains
- 15. Erosional Agents and Deposition Wind, water, and glaciers Carve, wear away, and remove rock and soil particles Material is deposited in new places New landforms are created
- 16. Running Water Most important erosional agent Ability to erode depends upon: Amount of precipitation Length and steepness of the slope Kind of rock and vegetation cover Load of a stream Materials transported by a stream Decline in velocity results in deposition Deltas: where streams meet bays, oceans, and lakes May be deposited in adjacent plains (floodplain)
- 17. Stream Landscapes Humid areas Waterfalls V-shaped channels Floodplains Meandering streams Oxbow lakes Natural levees Arid areas Lack of vegetation increases erosional forces Playas Alluvial fans Arroyos Washes Buttes and mesas
- 18. Groundwater Aquifer Porous underground structure bearing water Water table Upper level of the water within an aquifer Ponds, lakes, marshes, and streams form when land surface dips below the water table
- 19. Groundwater Solution Chemical process by which groundwater (particularly when combined with CO 2 ) dissolves soluble materials Significant effect on limestone Underground caverns, stalactites, stalagmites, sinkholes Karst topography Limestone region marked by sinkholes, caverns, and underground streams
- 20. Glaciers Huge mass of slowly moving land ice Covered a large part of the earth as recently as 10,000-15,000 years ago Form only where annual snowfall exceeds annual snowmelt and evaporation The weight of the snow causes it to compact at the base and form ice Ice at the bottom becomes like toothpaste and moves slowly
- 21. Glaciers Continental glaciers Mountain glaciers About 10% of the earth’s land is under ice Glaciers change landforms by erosion Scour the land as they move Glaciers create landforms when they deposit debris they have transported Till consists of rocks, pebbles, silt
- 22. Glacial Landforms Erosional Glacial troughs Fiords Tarns and cirques Arêtes Depositional Moraines Eskers Drumlins Outwash plains
- 23. Waves, Currents, and Coastal Landforms Cliffs Formed by wave action when land at the coast is well above sea level Beaches and spits Formed by the deposition of sand grains Longshore currents transport sand Sandbars Formed by sand deposited by the backwash of waves May expand to enclose lagoons or inlets Salt marshes may develop
- 24. Waves, Currents, and Coastal Landforms Coral reefs Composed of coral organisms growing in shallow tropical water Develop short distances offshore Atolls Reefs formed in shallow water around a volcano that has since been covered or nearly covered by water
- 25. Wind Most significant in dry climates Limited vegetation leaves exposed particles subject to movement by wind Dunes Produced by wind-driven sand Loess Deposit of windblown silt Rich soils usually form from loess deposits
- 26. Landform Regions Large section of the earth’s surface where a great deal of homogeneity occurs among the types of landforms that characterize it Mountains Plains Plateaus