Ch14 Flashcards
Internal processes build terrain Reshape crustal surface of earth Have taken place billions of years Effects don't work independently Cause earthquakes/volcanoes/ massive crustal rearrangement and operate to shape/reshape earth
Internal processes on landscape
- Continents seemed fixed from human perspective.
- till mid 20th century scientists believed earths continents were rigid.
- Supercontinent beliefs
- till recently idea not accepted
Rigid earth to plate tectonics
1915 Alfred Wegener Pangea “while land”
Wegener continental drift
-# of close affinities on both sides of Atlantic
-margines of SAmerica/Africa fit
Mountains in Scandinavia and British isles match Appalachian mountains
-mesosaurus both sides of Atlantic
Similar fossilized plants s America India Antarctica and Australia
- vast distributional coincidences
Supporting evidence Wegeners continental drift
Paleontology supports continental drift
Glaciated continents reconstructed make sense
Continents fit
Similar geologic feature on diff continent coasts
Extra evidence for Wegeners continental drift
1) crust was “too rigid” I permit large scale motions, how could solid rock plow solid rock ?
2) Wegener didn’t offer suitable mechanism that could displace large masses for a long journey
Why the theory was ignored and impossible
Plate boundaries
Sea floor spreading
Paleomagnetism
Convection and plate tectonics
Evidence of plate tectonics
Vast abyssal plains if undersea volcanoes
Seamounts
Theory proposing that Mid-ocean ridges are formed by currents of deep seated magma rising up from the mantle. (Often during Volcanic eruptions) creating new basaltic ocean floor (crust regions) that spreads away laterally from the ridge and creating the newest crust
Sea floor spreading
This process explains trenches. It is the sight where old crust descends and then is melted. These ocean trenches contain the oldest crust. Older lithosphere descends into asthenosphere in “” where it is “recycled” into the convective cycle that operates in earth.
Subduction
Earthquakes occur along this line
Correspond w/ locations of trenches and ridges on sea floor
Plate boundaries
- Iron on cooled magma orients itself w/the magnetic poles & provides record of past magnetic fields
- sea floor has a relative symmetrical pattern of magnetic orientation in both sides of ridges, indicating it has spread laterally by addition of new crust.
- used to find age of ocean floor (sea floor spreading)
- magnetic field has reversed more than 170 times
Paleomagnetism
Verification of “” by paleomagnetism and ocean floor core sampling
Seafloor spreading
Core holes drilled in the ocean show that Sediment age/thickness increase with distance from ridges.
Ocean floor cores/core sampling
Ocean floor cores proved Wegener wrong because both continents AND The “” are drifting by sea floor spreading
Lithosphere
-Theory behind the motion of lithosphere plates
- plates float on asthenosphere
- 7 major plates
- 7 intermediate
- 12 smaller
Plates are being subducted
Framework relates wide range of internal processes and topographic patterns.
Plate tectonics
- Slow convection in earths mantle
- convection can push plates away from each other
Driving plate tectonics
-Divergent boundaries
-Subduction zones
-Collision of India w/Eurasia
-Transform faults and boundaries
All evidence of
Plate boundaries
3 types of plate boundaries are
Converge toward
Diverge from
Slide laterally past
Plates move away from each other because Magma from asthenosphere wells up in between plates. Plutonic solidifies below. Represented by mist common, “mid ocean ridge” but also occurs within continent “continental Rift Valley” associated with shallow earthquakes and volcanic activity. “Constructive” because adds material to crust surface .
Divergence boundaries
Sea floor spreading is also known as
Divergence
Associated with 2 Plates colliding
“Destructive” normal type associated with one plate being subducted but showing crumpling at the edges where they meet. Removal or compression of crust.
Responsible for massive landforms
Mountain ranges/volcanoes/oceanic trenches.
3 types
Convergence boundaries
What are the three types
Ocean- cont convergence
Ocean -ocean convergence
Cont-cont convergence
The “” under rides the “” because its denser, which makes it sink into the asthenosphere through “subduction” . Usually Creates oceanic trench and coastal mountains. Accompanied by earthquakes along margins and volcanos along plates. -metamorphic rocks form. “Blue schist”
Ocean -continental convergence
Creates oceanic trench and volcanoes on ocean floor which initiate volcanic islands. ex(aleutians in Japan) Subduction in undersea trench formation -deep shallow earthquakes
Ocean ocean convergence
No subduction, crust is too buoyant. Causing Huge mountains like alps build up -Himalayas /volcanoes are rare- but shallow-focus earthquakes & regional metamorphism is common.
Cont-cont convergence
2 plates slip past each other laterally in a fault structure. “conservative”movement is parallel to the boundary -nor created new nor destroyed old crust. Associated with a great deal of seismic activity. San Andreas fault. produce shallow focus earthquakes.
Transform boundaries
Plate boundaries exist all around this “” basin. Primarily subduction zones.75% volcanoes all along plate boundaries/earthquakes. Home to millions. Mex. city. Tokyo. La. Largest metropolitan regions.
Pacific ring of fire. Pacific rim.
Location where molten mantle Magma rises to, or almost to, earths surface. locations near but not on plate boundaries. (Not volcanoes) Nearly 50+ identified. The cause is unknown but creates volcanos and hydrothermal (hot water) features.
Hot spots (mantle plumes)
Localized hot area not associated w/ plate boundaries.
Move w/ the plate eventually become inactive
Hot spot trail
Cause if Hawaiian islands looking like mushrooms. Research indicates they are more complex than recently observed. -seismic tomography suggests some “” may be shallow and others mobile.
Mantle plumes
Small to medium mass of lithosphere that is too buoyant to be subducted so instead fuzes (accretes- grows together-adheres) to a plate. often very diff. from the plate. bound on all sides by faults. Ex. Most of Alaska, W Canada. & West U.S, are a mosaic of accreted “”
Terranes
- Mid cont. mtns. Range formation (Appalachians)
- # of plates and their sizes have changed over earth history.
- why are there earthquakes in middle of continental plates.
- why are plates diff sizes
- why do they form where they do?
Plate tectonic remaining questions
term refers to all phenomena connected w/the origin and movement of magma from earths interior to or near the surface. An internal process directly associated with tectonic movement. THREE TYPES
Vulcanism
When molten magma expels onto surface while still molten
Extrusive vOlcanism
When magma solidifies in shallow crust near surface
Intrusive volcanism
Magma solidifies deep inside earth Far below the surface
Plutonic activity
Molten mineral material below surface extruded as lava
Magma
Rock fragments solidified lava blobs ashes and dust gas and steam may be hurled up in extraordinary quantities
Pyro clastic
3/4 volcanic activity undersea
Activity Associated w/ plate boundaries
Volcano distribution
Nature of volcanic eruptions apparently determined largely by the chemistry of magma that feeds it. Strength of surface/pressure of magma as well.
Magma chemistry & styles of eruption
Felsic, granite
High silica
Andesite dionite
Intermediate silica
Mafic basalt
Low silica
Temp. Features on landscape
Much of earths water originated from water vapor of volcanic eruptions its magma produces major elements for plant growth and fertility
Volcanic activity
Parallel flow to surface solidifies horizontally resembles strata of sedimentary streams flowing through lava cause an irregular fragmented surface . Form a hexagonal surface when cooled
Lava flow
Most of worlds extensive lava flows are from fissures/hot spots
-vast accumulations of lava that build up layer upon layer upon massive punts of ground.
Flood basalt
Basaltic lava flows over surrounding surface. Forms broad low lying gentle slope layer upon layer of solidified lava flows w/ little pyro clastic material.
Shield volcanoes
Emit higher silica “intermediate” lavas “andesite” symmetrical cone steep sided “strata volcanoes” steepness builds up by layers of ejected pyroclasts Held together by solidified lava flow pyroclastics and hardened mudflow 12000ft
Composite volcanoes.
Also called “ plug domes” masses of viscous lava high silica too thick /pasty to flow far. grows by expansion below and within. 2000ft. Irregular shape. Plug of lava covered by pyroclastics within crater of composite volcano
Lava dome
Smallest volcanic peaks. Basaltic most common. Steep Cone shapes built by pyroclastics ejected from volcanic vent. Size of particles determines slope steepness. Loose = Ash -small cinders & -larger 1500ft
Cinder comes
Produces when volcano explodes , collapses, or both. -immense basin shaped. Depression generally circular. Later diameter than original vents. Can become lakes.
Calderas.
Small sharp spire that rises abruptly above surrounding land and represents pipe/throat of old volcano. Filled with solidified lava after final eruption.
Volcano necks
Uphold -anticline
Downfold-syncline
Compressional
Stress. Rock must be hot
Folding
Caused by tensional stress ?
Compressional?
Shear stress?
Normal fault
Reverse fault
Strike slip fault
All cold
Through water vapor >acid rain that harms vegetation and causes corrosion. Droplets reflect incoming solar radiation that alters global weather and reduces insolation
Volcanic gases
Rare cause of life loss. +property damage. + speed/distance dependent on viscosity which depends in silica content.
(Low silica basaltic= fluid/fast)
(High silica andesite=thick/short distance down slope)
- viscosity rhyollitic lava barely squeezes out and bulges up in lava dome.
- no danger only in explosion it’s a hazard
Lava flow
Composite volcanoes/lava domes-violent ejection of pyro clastic material & gases. ?
Large solid rocks “bombs” drop immediately. Smaller ash/dust form enormous ?
Where ash may fall in quantities and can damage crops and cause buildings to collapse
Eruption column and eruption clouds
High speed avalanche at collapse of lava domes or rapid subsidence of eruption column fat speed avalanche of gases ash rock fragments am may disable aircraft engines
Pyroclastic flows
Composite volcanic hazards -loose mantle of ash and pyroclastic flow deposits on slope of volcanoes can be mobilized by heavy twin /melting of snow & glaciers during eruption
Volcanic mudflows (lahar)
Poking at historical eruptions and evidence to map out potential paths of pyroclatsic flows and lahars.
Tilt-meters to measure slope change in earthquake
Remote cameras ) time scale
Monitoring volcanic mudflows
Rock pushed upward before or after solidification and may change the surface shape
Igneous intrusion
Refers to intrusive igneous bodies of any size
Plutons
Rising magma makes room for itself by this or working upward “ore removal.
Stoping
Largest most amorphous intrusion enormous subterranean size. 100kilometer surface -core of mountain ranges
Batholiths
Similar but smaller igneous intrusion of indefinite depth
Stocks
Slow flowing viscous Felix magma forces between horizontal layers of preexisting rock. Builds into mushroom type overlying strata . Many are small some are so large they form the core of hills and mountains similar to batholiths
Laccoliths
Long thin intrusive body orientation determined by structure of preexisting rocks builds when magma basalt is forced between strata that are in place results in horizontal igneous sheet between horizontal sedimentary layers
Sills
Most wide spread of intrusive forms. Narrow. Formed by intrusion of vertical sheet of magma into preexisting rock. Erosion resistant.
Dikes
Least prominent among igneous intrusions. Widespread. Occur individually/in profusion. Thin formed when’s gems forced through small fractures on preexisting rocks also by melting from upward surge of magma. Generally vertical.
Veins
Deformation of earth crust
Tectonism/ diastrophism
Term refers to the deformation of earths crust, implies that the material is solid not molten TWO TYPES (whose separation is not always discrete or clear)
Diastrophism
The bending of crustal rocks by compression or uplift with great pressure & stress being applied for long periods. Varies from centimeters to 10's of kilometers. From simple symmetrical, to complex asymmetrical features. Types of "": Mono cline Anticline Syncline Overturn fold Overthrust fold
Folding -(1st type if diastrophism)
- a simple symmetrical upfold
- a simple downfold
Anticline
Syncline
Breaking apart of rock structures with Accompanying displacement. (Vertical horizontal or both) Crust moves-one or two sides break. Can vary (slow or sudden) (centimeters to 20-30ft.)(sudden slippage) up to hundreds of kilometers horizontally and 10’s of kilometers vertically(over millions of yrs) -usually related to earthquakes
Faulting
along zone of weakness in crust is called?
intersection of zone w/earth surface is called?
Fault zone
Fault line
The Result of tension stresses pulling apart or extending crust. Produces steeply inclined Fault plain & Fault scarp. One side pushed up, or “upthrown, other side down thrown. Displacement mostly vertical. Produces Horst and graben
Normal fault 1st type of fault
Fault produced from Compression stress. upthrown rises steeply above down thrown,(causing fault scarp to be severely over steepened if erosion didn’t act to smooth the slope) results in landslides. Displacement mostly vertical.
Reverse faults 2nd type of fault
Compression forces upward block to override the down thrown at low angle , complicated in structure
Thrust fault /overthrust fault 3rd type of fault
Horizontal fault produced by shearing stress with adjacent blocks being displaced laterally relative to each other.
Strike slip fault 4th type of fault.
Steep cliff formed by faulting, represents the edge of a vertically displaced block- one of the prominent topographic features that marks a fault line
Fault scarps
These landforms are associated with what type of fault?
Tilted fault block mountains
Horst &
Graben & rift valleys
Landforms associated w/ normal faulting
Mountain formed under certain conditions of Crustal stress where a fault block may be severely faulted and upthrown only on one side causing asymmetrical tilting producing a steep stope along fault scarp and gentle slope on other side of block
Tilted fault block mountain
An Uplift block of land between 2 parallel faults. land on both sides. down thrown produces mountain or plateau
Horst
Block of land bounded by parallel faults in which the block has been downthrown. Produces a distinctive structural valley with a straight steep sides fault scarp on either side.
Graben
Linear fault stream Shutter ridge& Sag ponds & Offset stream Landforms associated with
Strike slip faulting
Surface trace of a large strike slip fault is marked by a linear fault trough or valley formed by repeated movement and fracturing of rock within fault zone
Strike slip faulting
Pond formed by the collection of water from springs or runoff into sunken grounds. a Depression filled with water - results from the jostling of earth in the area if fault movement
Sag ponds
Stream across fault displaced by periodic fault movement or diverted when shutter ridge Is faulted in front of drainage channel. “Offset drainage channel;perhaps most conspicuous landform produced by strike slip faulting.
Offset stream
Vibration in earth produced by shock waves resulting in a sudden displacement along a fault
Earthquake
Energy released in an earthquake that travels outward in widening circles. moves through earth in seismic waves that originate at the “focus” which is the center of earthquake
Earthquake waves
The strongest shocks & greatest crust vibrations felt on the ground right above the focus”of earthquake is called..
Epicenter
Fastest moving earthquake waves, move through earth like sound waves.alternately compressing and relaxing the material they pass through. 1st to be felt initial jolt followed by strong side to side and up and down shearing motion, of slower moving S waves “body waves”. Who are also strong side to side and up and down “shearing” motion. Third wave after S does “rolling” motion.
P waves
Instrument used to record earthquakes. can pinpoint earthquake focus w/great precision by measuring lag time between p and S waves
Seismographs
Relative amount of energy released during an earthquake. calculated in “logarithmic scale” so there’s an energy energy increase from one magnitude to the next if about 32 times.
Magnitude
A scale for earthquake magnitudes. devised be CA seismaologist Charles F. Ritcher 1935 to describe the amt. of energy released in a single earthquake. Most commonly quoted earthquakes magnitude of 7 or higher.
Richter scale
Shaking intensity» moment magnitude (most commonly used to describe large earthquakes) & the most widely used intensity scale “” that assigns the strength of local shaking based on observed effects and damage.
The modified mercalli intensity scale
Ground shaking causes most damage. but generally diminishes from distance of epicenter. Loose unstable soils amplify the shake.
When loose water, saturated sediments turn fluid it results in subsidence, fracturing, and horizontal sliding of the ground surface. -liquefaction -landslides
Very long sea waves generated by submarine earthquakes or volcanic eruptions. -tsunamis.
Earthquake hazards
=isostasy
=Plasticity
=Pangea
Theories of plate tectonics
Maintenance of hydrostatic equilibrium of earths crust. Basically where material is added crust will sink but will rise when material is removed.
Isostasy
Theory of continental drift proposes that continents were originally all connected but broke up and are still drifting apart so will continue to change position. The “” was the massive supercontinent that Alfred wegener postulated to have existed about 250,000,000 yrs ago. Evidence includes a # of close affinities of geologic features on bothe sides of Atlantic and the continental margins of sub equatorial portions of Africa and South America fit together
Pangea
Theory that our earth is not cemented in place but continues to move
Plasticity
Oceans have a continuous system of large ridges located some distance from continents often mid ocean. Deep trenches occur at many places in the ocean floors often around margins of ocean basins. This is evidence of
Plate tectonics
Displaces streams flowing across a fault.
Shutter ridge
A valley marking a strike slip fault, occurs by repeated movement and fracturing of rock.
Linear fault trough.
