Chapter 14 The Internal Processes.doc

1、Chapter 14: The Internal ProcessesI. The Impact of Internal Processes on the LandscapeA. internal processes are the supreme builders of the terrainII. Crustal RearrangementA. Plasticity 1. igneous rocks of the upper crust occur in 2 layersa. sima: lower layer1) oceanic crust; partially underlies con

2、tinents too2) 2 dominant mineral compounds: silica and magnesium3) alkaline, dark, relatively young, basaltic, relatively dense b. sial: upper layer1) continental crust2) immense bodies of rock at least partially embedded in the sima3) 2 dominant mineral compounds: silica and aluminum4) more acidic,

3、 lighter in color, generally granitic, less dense 2. concept of plasticity replaced theory of rigidity: a. lightweight granitic material floats on a foundation of denser basaltic materialb. continents free to move B. Isostacy 1. maintenance of hydrostatic equilibrium in the crust2. addition of signi

4、ficant amount of mass on portion of crust causes crust to sink; removal of a large mass causes crust to rise 3. causes:a. deposition of large amount of sediment on a continental shelfb. accumulation of glacial icec. weight of water trapped behind a damC. Continental Drift1. continents are quite mobi

5、le2. history of theorya. geographer Abraham Ortelius 1590sb. philosopher Francis Bacon 1620c. meteorologist Alfred Wegener 1920s3. Wegeners theory:a. Pangaea: super continent existed 250 million years agob. broke up into large sections that continue to move today4. Wegeners evidence:a. continental m

6、argins of South America and Africa fit togetherb. petrologic and paleontologic records on both sides of Atlantic match upc. ancient glacial deposits and fossilized plant remains match up across continents5. response to Wegeners theory: disbeliefIII. Plate TectonicsA. The Evidence1. theory of seafloo

7、r spreading a. the theory:1) oceanic ridges are formed by currents of magma rising up from the mantle and spreading laterally2) oceanic ridges contain newest crust formed on planet3) subduction: descent of the edge of a lithospheric plate under the edge of an adjoining plate, involving melting of th

8、e subducting material4) amount of new crust formed is compensated for by amount lost at subduction zoneb. oceanic v. continental crust1) oceanic crust has short lifea) within 200 million years its returned to the mantle by subductionb) average age = 100 million years2) lower density continental crus

9、t cannot be subducted a) virtually permanent b) some continental crust is 4 billion years old c. confirmation of theory of seafloor spreading1) paleomagnetism: relatively symmetrical pattern of magnetic orientation on both sides of oceanic ridges2) core sampling: sediment thickness and seafloor age

10、increase with increasing distance from the oceanic ridges d. seafloor spreading is quite rapid: about as fast as fingernails grow2. theory of plate tectonicsa. lithosphere is mosaic of rigid plates floating over the underlying plastic asthenosphereb. 13 major plates are postulated; equal number of s

11、maller platesc. plates 60 miles thickd. most plates consist of both oceanic and continental cruste. rates of seafloor spreading vary:1) 7,000 years ago cataclysmic eruption of Mount Mazama 2) 4,000 foot deep caldera8. Volcanic Necks a. small, sharp spire that rises above surrounding landb. remnant o

12、f pipe or throat of an old volcano that filled with solidified lava after its final eruption9. People and the Environment: Volcanic Hazardsa. risk in US: Washington, Oregon, California, Alaska, and Hawaii b. risks associated with volcanoes:1) Volcanic gasesa) water vapor, carbon dioxide, sulfur diox

13、ide, hydrogen sulfide and fluorineb) resulting hazards: acid rain; block incoming solar radiationc) Mount Pinatubo (1991): decreased insolation lowered global temperatures slightly for more than a year2) Lava Flowsa) lava flows rarely cause loss of life but can produce significant property loss b) s

14、hield volcanoes low silica, basaltic lava quite fluid and fast moving, but generally follow predictable pathsc) composite volcanoes high silica, andesite lava thicker and more sluggish, moves only short distances3) Eruption Column and Cloudsa) produced by composite and lava dome volcanoes that erupt

15、 explosivelyb) volcanic bombs and ash4) Pyroclastic Flows (nue ardent)a) high-speed avalanche of searing hot gases, ash, and rock fragmentsb) speeds 100 mphc) Mont Pelee, Martinique 1902: killed nearly all 20,000 residents of St. Pierre5) Volcanic Mudflows (Lahars)a) composite volcano hazardb) heavy

16、 rain or melting of snow or glacier during an eruption mobilizes the loose mantle of ash and pyroclastic flow depositsc) typically flow down stream valleys d) can reach speeds 30 mph and travel 50 milese) Nevada del Ruiz, Colombia (1985): inundated town of Armero, 30 miles away, and killed 20,000c.

17、The 1980 Eruption of Mount St. Helens1) Cascade Range, Washington2) dormant for 123 years3) killed 57 peopled. Potential for Future Eruptions in the Pacific Northwest1) ongoing subduction of the Juan de Fuca and Gorda plate beneath North America 2) Cascade Range: Lassen Peak, CA Mount Garibaldi, Bri

18、tish Columbia3) 12 potentially active volcanoes; 7 have shown activity since late 1700s4) rapidly expanding population in region volcanoes of the Cascades potentially some of most dangerous in North America C. Intrusive Vulcanism1. igneous intrusion: igneous rock that is pushed upward into the Earth

19、s crust either before or after solidificationa. may be subsequently exposed at surfaceb. usually resistant to erosion2. stoping: process by which rising magma makes room for itselfa. molten magma can assimilate the rock being invadedb. contact metamorphism occurs adjacent to the area of magma invasi

20、on as a result of the heat and pressure of the rising intrusion3. types of igneous intrusions:a. Batholiths: subterranean igneous body of indefinite depth and enormous size (surface area of at least 40mi2)1) often form the core of major mountain ranges2) bedrock of the following consist of batholith

21、ic granite, which was exposed as the overburden of other rock has been eroded away:a) Sierra Nevadas, Californiab) Sawtooth Mountains, Idahoc) Colorados Front Range b. Stocks: a small body of igneous rock intruded into older rock; similar to batholith but smallerc. Laccoliths: an igneous intrusion p

22、roduced when slow-moving viscous magma is forced between horizontal layers of preexisting rock, forming a mushroom shaped mass that domes the overlying strata1) some form cores of hills or mountains: a) Black Hills, South Dakotab) southern Utah mountain groups: Henry, Abajo, LaSal2) pluton: any larg

23、e intrusive igneous body; includes batholiths, stocks, and laccolithsd. Dikes: vertical or nearly vertical sheets of magma that are thrust upward into preexisting rocks1) most widespread of all intrusive forms2) vertical, narrow, erosion-resistant3) often found in association with volcanoes, occurri

24、ng as radial walls extending outward like spokes:a) Shiprock, New Mexicob) around the Spanish Peaks, Coloradoe. Sills: a long, thin intrusive body that is formed when magma is forced between parallel layers of preexisting rock to solidify eventually into a sheet1) often horizontal igneous sheet betw

25、een horizontal sedimentary layers2) can serve as caprock, producing a steep-walled mesa or buttef. Veins: small, igneous intrusions, usually with vertical orientation1) commonly formed when molten material forces itself into small fractures in preexisting rocksV. Diastrophism A. deformation of Earth

26、s crust1. solid, not molten, material2. particularly obvious in sedimentary rocksB. types:1. folding2. faultingVI. FoldingA. folding: bending of crustal rock by compression and/or uplift1. slow, plastic deformation rather than fracturing2. can occur in any type of rock, but is most visible in sedime

27、ntary strataB. types of folds:1. monocline: a one-limbed fold connecting horizontal or gently inclined strata2. anticline: simple symmetrical upfold3. syncline: simple symmetrical downfold4. overturned fold: upfold that has been pushed so vigorously from one side that it becomes oversteepened enough

28、 to have reverse orientation on the other side5. overthrust fold: when the oversteepened limb breaks and shears, resulting in older rock overriding younger rockC. topographic results1. series of long, narrow, parallel ridges and valleys where folds occur in multiples2. normal, initial result:a. anti

29、clinal ridges b. synclinal valleys 3. inverted topography result of tension cracks, compression and erosion:a. anticlinal valleysb. synclinal ridges4. Appalachian Mountains ridge-and-valley topography5. Swiss Alps complex compressional foldingVII. FaultingA. faulting: when rock is broken with accomp

30、anying displacement1. fault zone: faulting takes place in zones of weakness in the crust2. fault line: intersection of fault zone with the Earths surface3. fault movement can be vertical or horizontal or combination of botha. movement can be very slow or occur as sudden slippageb. earthquakes can oc

31、cur with abrupt movements4. fault-line topographic features:a. fault scarp: steep cliffs that represent the edge of a vertically displaced block1) eastern face of Sierra Nevadas, California (fig 14-39)2) western face of Wasatch Range, Utahb. linear erosional valleysc. displaced stream coursesd. sag

32、pondsB. Types of Faults1. 4 principal types of faultsa. normal fault 1) tension stresses2) primarily vertical movement: steeply inclined fault zone with upthrown block of land on one side relative to downthrown block on other side3) prominent fault scarpb. reverse fault 1) compression stresses2) pri

33、marily vertical movement: upthrown block rises steeply over downthrown block severely oversteepened fault scarp3) often landslidesc. strike-slip fault1) primarily horizontal movement2) adjacent blocks are displaced laterally3) topographic features:a) sag ponds b) offset streams d. overthrust fault1)

34、 compression forces the upthrown block to override downthrown block at low angle2) older rock overlying younger rock2. Prominent Faulted Landscapea. Fault-Block Mountains 1) a surface block that is severely faulted and upthrown on one side without any faulting or uplift on the other2) block is tiled

35、 asymmetrically steep slope along the fault scarp and relatively gentle slope on other side of the block3) Sierra Nevadas, California (Fig 14-39): eastern face is fault scarp with 2 mile vertical reliefb. Horst 1) uplift of block of land between 2 parallel faults2) block elevated above surrounding l

36、andc. Graben 1) downthrown block of land between 2 parallel faults2) Death Valley, California3) basin-and-range country of western interior of US, encompassing most of Nevada: vast sequence of horsts and grabens, mixed with fault-block mountains d. Rift Valleys 1) downfaulted grabens that extend for extraordinary distances as linear valleys enclosed between steep fault scarps2) Great Rift Valley of East Africa C. Focus: Earthquakes1. earthquake: vibratio