GEOG 140
Intro Physical Geography
Lecture Notes
The Dynamic Planet
The Pace of Change
-uniformitarianism
-same processes active in the environment today have been operating throughout
geologic time
-catastophism
-landforms are young and the result of catostophic events
-little evidence
-reality appears to be uniformitarianism mixed with catastrophic events
-punctuated equilibrium
Earths Structure and Internal Energy
-Earth’s Core
-inner core
-outer core
-Earth’s Mantle
-Earth’s Lithosphere and Crust
The Geologic Cycle
-The Rock Cycle
-Igneous Processes
-igneous rocks
-form from the cooling of molten magma (lava)
-at the surface (extrusive)
-faster cooling-finer mineral crystals
-inside the crust (intrusive)
-slower cooling-larger mineral crystals
-intrusive and extrusive igneous rocks
-concordant-does not disrupt existing strata
-laccolith-pluton with a domelike structure that pushes
overlying strata into a bulge without destroying them
-sill-thin horizontal layer formed between two sedimentary
strata
-discordant-cuts across existing strata
-batholith-pluton that has melted and assimilated
surrounding rock
-dike-vertical barrier wall cutting across sedimentary strata
-classifying igneous rocks
-magma composition
-rich in feldspar and silica (acidic/felsic)
-light colored rocks rich in feldspar and quartz
-poorer in silica (basic/mafic)
-darker rocks
-intrusive-gabbro
-extrusive – basalt
-Sedimentary Processes
-lithification processes
-cementation
-compaction
-hardening
-most result from the deposition and compaction of rock fragments and
mineral grains derived from other rocks (clastic)
-grains broken away from existing rocks and transported to new locations
-weathering
-chemical
-physical
-erosion and transportation
-successive layers deposited at the bottom of water bodies
-primarily oceans and seas
-processes of compaction and cementation
-examples
-conglomerate
-comprised of gravels, pebbles, possibly boulders
-well rounded indicating transport by water
-breccia
-pebble size fragments in a conglomerate are angular
-sandstone
-sand size grains-usually quartz
-rounded or angular depending on distance transported
-variations in particle size and irregular shapes
-poor sorting and rapid deposition
-shale
-finest grained clastic sediment
-compacted mud (clay minerals as opposed to quartz)
-limestone (chemical sediment)
-comprised of marine shells fragments or ancient coral
reefs (lithified calcium carbonate)
-stratification
-cross bedding (ripple marks/sand dunes)
-Metamorphic Processes
-rocks altered by heat and pressure
-igeneous rocks can be remelted and recrystallized
-sedimentary rocks can be fused by heat and pressure into much
harder rocks
-metamorphic rocks can also be transformed
-metamorphic rocks comprise the ancient roots of mountains
-examples of metamorphic rocks
-sandstone into quartzite
-limestone into marble
-shale into slate
-??? into schist
Plate Tectonics
-eight major and at least ten smaller plates
-plate boundaries take on three kinds of character
-divergence or spreading
-convergence or collision
-transform or lateral displacement
-Seafloor Spreading and the Production of New Crust
-divergence
-midoceanic ridges-seafloor spreading
-magma wells up from the athenosphere
-new lithosphere is created
-lithosphere on opposing sides of the ridges is pushed apart
-crust at these sites is thin-rifting occurs
-ocean crust is young (no older than 208 million years)
-Subduction of the Crust
-convergence
-plates spreading outward must converge and collide at other points
-continental crust has lower density than oceanic crust
-it is “lighter”
-when oceanic and continental plates meet the continental plate overrides the
oceanic plate and pushes it downward
-subduction
-subducted plate is melted by the athenosphere
-molten rock forces its way up through vents and fissures to the surface
-volcanism
-plate movement at these sites also results in earthquakes
-Plate Boundaries
-divergent boundaries
-midoceanic ridges-seafloor spreading
-also happens on land-crustal spreading
-rift valley
-eastern Africa
-Red Sea (advanced stage of rift valley)
-convergent plate boundaries
-three types
-oceanic-continental plate convergence
-example - Nazca plate subducting beneath South American Plate
-oceanic-oceanic plate convergence
-example- Pacific, North American, Eurasian, and Australian plates
create island arcs in northern and western pacific
-Aleutian Islands and Japan
-continental-continental plate convergence
-example – Eurasian plate and Indian plate
-no melting-thickening of land instead
-earthquakes but no volcanism
-transform plate boundaries
-plates slide past each other-transform faults
-example- San Andreas fault
-Earthquake and Volcanic Activity
-high correlation between plate boundaries and the occurrence of volcanic activity
and earthquakes
-Hot Spots
-fixed points of upwelling material arriving in tall plumes from the mantle
-Hawaiian Islands/Emperor Seamounts