Transcript
Overview Earth Materials Geologic Time Movements of the
Continents Tectonic Forces Gradational Processes Landform Regions
Earth Materials Igneous Rocks Sedimentary Rocks Metamorphic Rocks
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
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
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
Geologic Time Earth formed about 4.7 billion years ago Theory of continental drift
Based on early 20th-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
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
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
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
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
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
Gradational Processes Reduction of the land’s surface
Weathering Mass movement Erosion
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
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
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
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)
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
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
Groundwater Solution
Chemical process by which groundwater (particularly when combined with CO2) dissolves soluble materials
Significant effect on limestone Underground caverns, stalactites, stalagmites, sinkholes
Karst topography Limestone region marked by sinkholes, caverns, and
underground streams
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
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
Glacial Landforms Erosional
Glacial troughs Fiords Tarns and cirques Arêtes
Depositional Moraines Eskers Drumlins Outwash plains
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
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
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
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
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