EXAM #2
silica-rich magmas
may produce explosive clouds of hot ash and transition into plumes termed "eruption columns". When this magma ascends, the gas bubbles cannot escape easily and result in the magma expanding which adds more pressure to the volcano, causing in possible fracturing if pressure exceeds the strength of the rock
decompression melting
melting that occurs as rock ascends due to a drop in confining pressure
composite cones (stratovolcanoes)
most are located in a narrow zone that surround the pacific ocean (ring of fire). Very, large symmetrical structure composed of lava & pyroclastic deposits. May generate explosive eruptions or erupt quietly. Ex. Fujiyama, mount mayon, vesuvius
Subduction zone
a long narrow zone where one lithospheric plate descends beneath another
reversed polarity
a magnetic field opposite that which exists at present
Normal polarity
a magnetic field that is the same as that which exists at present
viscosity
a measure of a fluid's resistance to flow
intensity
a measure of the degree of earthquake shaking at a given locale based on the amount of damage
volcano
a mountain or hill, typically conical, having a crater or vent through which lava, rock fragments, hot vapor, and gas are being or have been erupted from the earth's crust.
Deep-ocean trench
a narrow, elongated depression on the floor of the ocean
liquefaction
a phenomenon, sometimes associated with earthquakes, in which soils and other unconsolidated materials containing abundant water are turned into a fluidlike mass that is not capable of supporting buildings.
Pangaea
a proposed supercontinent that 200 million years ago began to break apart and form the present landmasses
tsunami
a rapidly moving ocean wave generated by earthquake activity that is capable of inflicting heavy damage in coastal regions
Rift valley
a region of earth's crust along which divergence is taking place
domes
a roughly circular upfolded structure similar to an anticline
lava tubes
a tunnel in hardened lava that acts a horizontal conduit for lava flowing from a volcanic vent. Lava tubes allow fluid lavas to advance great distances
aa flows
a type of lava flow that has a jagged, blocky surface
ductile deformation
a type of solid-state flow that produces a change in the size and shape of a rock body without fracturing. Occurs at depths where temperatures and confining pressures are high
fumarole
a vent in a volcanic area from which fumes or gases escape
parasitic cone
a volcanic cone that forms on the flank of a larger volcano
lahar
mudflows on the slopes of volcanoes that result when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels
Good Friday Alaskan earthquake
occurred in 1964 lasted for 2 to 4 minutes and had a 9.4 magnitude. 131 dead
Triangulation
of three or more seismic stations record an earthquake we can draw circles corresponding to the distance to the earthquake around each station. The intersection of these circles will indicate the location of the earthquake.
the role of heat
on average, temperature increases 20°C to 30°C per kilometer in the upper crust. This change in temperature is known as the geothermal gradient. At high temps, rocks in the upper mantle are near their melting point and in some locations, partial melting may occur
Plates
one of numerous rigid sections of the lithosphere that move as a unit over the material of the asthenosphere. Also called lithosphere plate, tectonic plate
bombs
particles larger than lapilli made of incandescent lava
blocks
particles larger than lapilli, made of hardened lava
Trans faults and strike-slip faults through the continental coast
slip faults through the continental coast- these faults may generate large earthquakes that occur on a cyclical basis.
Stocks
smaller intrusive bodies. May actually be a batholith but have not been fully exposed. Less than 100km^2 rock exposed.
Factors that contribute volcano's eruption intensity
the magmas composition the magmas temperature the magmas amount of dissolved gasses
partial melting
the process by which different minerals in rock melt at different temperatures
geothermal gradient
the rate of change in temperature with depth. the average is 30 degrees Celsius per km in the upper crust
seismogram
the record made by a seismograph
seismology
the study of earthquake waves; dates back to attempts made in china almost 2000 years ago to determine the direction from which these waves originated
ring of fire
the zone of active volcanoes surrounding the pacific ocean
Circum-Pacific Belt
the zone of intense seismic activity that encompasses the coastal regions of Chile, Central America, Indonesia, Japan, and Alaska, including Aleutian Islands.
moment magnitude scale
this can be calculated from the field studies of fault displacement, the area of the rupture surface, and the strength of the faulted rock. Also calculated by using seismograms by evaluating long period seismic waves
intraplate activity
this igneous activity is not associated with a plate boundary. This results from excessive hot mantle material (100°-150°C hotter than normal) termed a mantle plume rising to the surface. The area in which this basaltic magma erupts is termed a hot spot.
Whole-mantle convection
this model accounts for the oceanic material at depths greater than 660km and also illustrates mantle plumes originating from the core-mantle boundary. Some versions of this method indicate subducted oceanic material descends to the core-mantle boundary, melts, and then begins to rise as a mantle plume.
Mechanism Reid proposed for earthquake formation
-Existing fault or break in the rock -Tectonic forces are beginning to deform the rock -Slippage occurs at the weakest point and displacement will generate stress along the fault. Resulting in additional slippage and the release of the stress -This slippage allows the rock the "snap back". The vibrations of an earthquake are actually the rock elastically returning to its original shape
Average rate of plate movement worldwide
2-3 inches per year
continental crust
25-45 miles thick, upper portion is granodiorite (granite), lower portion is similar to basalt, density of 2.7 g/cm3, up to 4 billion years old
oceanic crust
5 miles thick. Compose of basalt. Density of 3.0 g/cm3 180 million years old or less
Concentration of gases in magma
70% water vapor 15% carbon dioxide 5% nitrogen and smaller amount of chlorine, hydrogen, and argon
Transform fault boundary
A boundary in which two plates slide past one another and accommodates motion between two plates.
Volcanic island arc
A chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another. Also known simply as an island arc.
outer core
A liquid layer that 2,270 km thick. Movement of iron in the layer generates the Earth's magnetic field
seismic sea wave
A rapidly moving ocean wave generated by earthquake activity that is capable of inflicting heavy damage in coastal regions
Divergent plate boundary
A region where the rigid plates are moving apart, typified by the mid-ocean ridges
plutons
A structure that results from the emplacement and crystallization of magma beneath the surface of Earth.
Explain continent positions through time since the breakup of Pangaea
Africa and North America moved apart 180 million years ago 130 million years ago South America rifted from Africa Australia separated from Antarctica 50 million years ago India began interacting with Asia approximately 45 million years ago In the last 20 million years Arabia rifted from Africa. The Baja separated from Mexico and the Panama Arc joined North and South America
continental drift
Alfred Wegener proposed the idea in 1915, suggesting that a super continent (Pangaea) once existed, surrounded by a large ocean named Panthalassa. About 200 million years ago Pangaea began breaking apart, and smaller continents began drifting to their present locations. Evidence provided was 1)The fit of South America and Africa- 2) Geographic distribution of fossils: Mesosaurus fossil only found in Permian shales of eastern south America and southern africa; also Glossopteris. Grew only in cool climates. Wegener utilized distribution of present-day organisms to support his hypothesis, ie Australian marsupials and the opossum marsupial of the Americas. 3)similar rock types/formations; Wegener cited a 2.2 billion years old igneous rock in Brazil that matched a similar aged rock in Africa 4)ancient climates: Climate change in Australia, India, South America, Africa, seeing glacial, erosional, and depositional in the south portions when they drifted to hotter climates. They used to be connected at a lower altitude with antarctica.
Describe the formation and characteristics of a tsunami
Can travel almost undetected across the ocean at speeds between 300 and 600miles per hour. Wave height is usually less than 1 meter and the wavelength are between 100 and 700 km. firs warning of a tsunami is the rapid retreat of water from the beach. Typically, there are several waves that impact the coast.
Briefly explain the general consensus among scientists to explain what drives plate motion
Connective flow in the mantle slab pull ridge push slab suction
Describe the evolution of convergent plate boundaries and the associated features with this physiographic region including oceanic-continental, oceanic- oceanic, and continental-continental convergence
Convergent plate boundaries occur where two lithospheric plates move toward each other. As the oceanic plate slides beneath the other plate, it actually bends producing a deep-ocean trench. The area where an oceanic plate descends into the asthenosphere is called a subduction zone. This develops because the descending plate has a higher density than the asthenosphere beneath it. Oceanic lithosphere is more dense than the asthenosphere while the continental lithosphere is less dense than the asthenosphere. The angle of subducting is 45°
inner core
Due to increased pressures, the iron in this layer acts as a solid. Has a radius of 1,216 km
describe some basic details of some Earth's major earthquakes
Earthquake can be generated by nuclear explosions or volcanic eruptions. Are the results of displacement of rock. The focus is the point within the Earth where the rock displacement generates the release of energy.
Explain how seismic waves are used to identify Earth's interior layers
Earthquakes produced semis waves that travel all the way to the other side of the Earth. Approximately 100-200 times a year. They do not travel along a straight path. They are reflected, refracted, and diffracted as they propagate. Seismic waves also move in curved paths.
deformation
General term for the processes of folding, faulting, shearing, compressions, or extension of rocks
the eruption of Mt St Helens
Erupting on Sunday May 18, 1980, the largest volcanic eruption to occur in North America in history. Summit had been more than 2900 meters above sea level, only to be lowered by more than 400 meters. The eruption claimed 59 lives, dying from the intense heat and suffocating cloud of ash and gasses (nearly one cubic kilometer blown 11 miles into the atmosphere), while other died from the impact or being trapped by mudflows. Trees within a 400km2 area were flattened and mudflows flowed 18 miles down the Toutle River.
fault creep
Gradual displacement along a fault. Such activity occurs relatively smoothly and with little noticeable seismic activity.
The two models to illustrate mantle convection
Layering at 660km (layer cake model)- Whole-mantle convection
magma's composition
Magma's viscosity is directly related to silica content... the more silica, the greater the viscosity. Magmas that produce basaltic rocks contain approximately 50% silica and magmas that produce granitic rocks contain over 70% silica. This is due to silicate structures linking in long chains before crystallization even begins.
Magnetite
Mineral that is primarily used in Paleomagnetic studies
divergent plate boundary
Most magma is produced along the mid-ocean ridge system associated with seafloor spreading. Lithospheric plates are moving apart and the reduction in overlying pressures causes rocks to melt without the addition of heat, Magma is generated is of basaltic composition, Most spreading centers are located in the ocean
Describe the evolution of divergent plate boundaries and the associated features with this physiographic region
Mostly occur in the ocean, except for Africa, Arabian Peninsula, and the red sea where it happens on land. Along divergent boundaries in the ocean, the seafloor is elevated generating the oceanic ridge. Along the axis of the many ridge segments, a deep downfaulted structure develops termed a rift valley. The process by which divergent plate boundaries generates new ocean floor is termed seafloor spreading averaging at a rate of 5cm/yr. As oceanic material is generated, it is relatively hot and occupies more volume than cooler seafloor Divergence can also occur on continents. The splitting of a continent develops an elongated depression called a continental rift. (east African rift valley) If this rifting continues, the rift valley will lengthen and deepen until it reaches sea level. (red sea). If rifting still continues, the linear sea will be transformed into an ocean basin (atlantic ocean).
Continental volcanic arc
Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. Examples include the Andes and the Cascades.
Earth's Seven Major plates and intermediate sized plates
North American South American Pacific African Eurasian Australian-Indian Antarctic Intermediate sized: Caribbean, Nazca, Phillipine, Arabian, Cocos, Scotia, and Juan de Fuca
Modified Mercalli Scale
Originally developed by Giuseppe Mercalli in 1902 to assess the damage from a quake at specific location. This scale is meaning to those affected but does not truly measure the earthquake's actual energy release. It also does not account for quakes too deep to be destructive. Measures damage.
epicenter
Point on Earth's surface directly above an earthquake's focus
syncline
a linear downfold in sedimentary strata: the opposite of anticline
elastic deformation
Rock deformation in which the rock will return to nearly its original size and shape when the stress is removed
difference between sills from buried lava flows
Sills have economic ore deposits. Sills are forming between rock layers, while the lava flows form at the Earth's surface, subsequently buried. Sills have vesicular textures, due to gases escaping.
Plate tectonics
Tested theory proposing that Earth's outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself
Over 1 million
The amount of earthquakes that happen every year
Yellowstone-type calderas
The collapse of a large area resulting from the extensive rease of silica rich pumice and ash along ring fractures
Crater Lake-type calderas
The collapse of the composite cone summit following an explosive eruption of silica rich pumice and ash.
Hawaiian type caldera
The collapse of the top of a shiled volcano caused by underground drainage of the magma chamber
Andean-type mountain systems
The first stage of development is passive and not associated with a plate boundary. At some point the continental margin becomes active and a subduction zone forms as the oceanic plate descends beneath the continental plate. Belts two zones: the volcanic arc and accretionary wedge.
Describe how the arrival times of P and S waves and triangulation are used to locate the epicenter of an earthquake
The greater the interval between their arrival, the greater the distance to the earthquake source. Triangulation
focus
The location where slippage begins
Paleomagnetism
The natural remnant magnetism in rock bodies. The permanent magnetization acquired by rock that can be used to determine the location of the magnetic poles and the latitude of the rock at the time it became magnetized.
megathrust fault
The plate boundary separating a subducting slab of oceanic lithosphere and the overlying plate.
orogenesis
The processes that collectively result in the formation of mountains.
hanging wall
The rock surface immediately above a fault
pyroclastic material
The volcanic rock ejected during an eruption, including ash, bombs, and blocks
P waves
These push (compress) and pull (expand) rocks in the direction they are traveling. Solids liquids, and gasses resist changes in volume, therefor they will spring back when the force is removed. Will travel through solids, liquids, and gases. Aka compressional waves
Alpine-type mountain building
This type of mountain building is characterized by extensive folding and faulting which results in the shortening and thickening of crustal material. The Himalayas are an example of this. Other areas include the Appalachians, alps, and Urals.
paleomagnetism
Today's Earth's magnetic field results in compasses point nort. Certain minerals such as magnetite, will retain this magnetism when they crysatllize. These rocks/ minerals that formed thousand or millions of years ago and contain a record of the direction of the magnetic poles at that time are said to possess "fossil magnetism"
volatiles
Water content plays a major factor in determining the temperature at which a rock will melt. Volatiles cause rocks to melt at lower temperatures. Water is important factor in magma generation along subduction zones.
folds
a bent rock layer or series of layers that were originally horizontal and subsequently deformed
Converging plate boundary
a boundary in which two plates move together, causing one of the slabs of lithosphere to be consumed into the mantle as it descends beneath an overriding plane
basins
a circular downfolded structure
vent
a conduit that connects a magma chamber to a volcanic crater
fissure
a crack in rock along which there is a distinct separation
terrane
a crustal block bounded by faults, whose geologic history is distinct from the histories of adjoining crustal blocks
strike-slip fault
a fault along which the movement is horizontal
dip-slip fault
a fault in which the movement is parallel to the dip of the fault
anticline
a fold in sedimentary strata that resembles an arch
pyroclastic flow (nuee ardente)
a highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground
caldera
a large depression typically caused by collapse or ejection of the summit area of a volcano
accretionary wedge
a large wedge-shaped mass of sediment that accumulates in subduction zones; Here sediment is scraped from the subducting oceanic plate and accreted to the overriding crustal block
pahoehoe flows
a lava flow with a smooth to ropey surface
3 types of volcanic activity
active, dormant, extinct ring of fire volcanoes of the deep-ocean basin irregularly distribute on the interiors of continents
fluid basaltic magmas
allow expanding gases to vent with relative ease. Eruptions are generally quiescent
magmas amount of dissolved gasses
also affects mobility. Water dissolved in magma decreases viscosity because it breaks that silicon-oxygen bond. Since the volatiles are lost when the molten material reaches the Earth's surface, lava tend to become more viscous
Island arc-type mountain system
also called Aleutian-type. When two oceanic plates converge, partial melting of the subducting plate generates magma. When the magma extrudes it generated volcanic island arcs.
Seismograph
an instrument that records earthquake waves. aka seimsmometer
volcanic neck
an isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano
dikes
are sheet-like (tabular) bodies. Oriented vertically. Can have thickness that range from less than a centime to more than a kilometer and lenghts up to hundreds of kilometers. When exposed to erosion, they have the appearance of a wall.
convergent plate boundary
as oceanic crust begins to subduct, an increase in temp & pressure drives off volatiles. These fluids migrate upward to form a wedge-shaped piece of mantle between the subducting and overring plate. Once this slab reached a depth of approximately 100 to 150 kilometers the rocks begin to melt generating a magma of basaltic composition. Over time, this magma rises and forms a linear/slightly curved chain of volcanoes called volcanic arcs. When oceanic lithospheric materials subducts beneath continental lithosphere, continental volcanic arcs form
mesosphere
below the asthenosphere, increase pressures counteract the increased temperatures allowing the rocks to strengthen... this layer acts as a solid. This layer is located between the depths of 660 km and 2,900 km within the Earth.
Cinder Cones (Scoria Cones)
built from ejected lava fragments. Most abundant type of the major volcanic types. Relatively steep sloped (up to 40°). Possess large, deep craters relative to their small size. Over ½ produced in one month and 95% were produced in one year. Ex. Parictuin located 200 miles west of Mexico City.
Cordilleran-type mountain building
collision and accretion (joining together) of small crustal fragments (terrane) to a continental margin has generated many of mountainous regions around the Pacific Ocean.
core
composition is thought to be an iron-nickel alloy with minor amounts of oxygen, silicon, and sulfur. Approx. 2164 miles thick. Has an average density of 11 g/cm3 but near the Earth's center the density is thought to reach 14 g/cm3
lithosphere
consists of the crust and the upper mantle. This layer tends to act as a single unit that exhibits rigid behavior. Thickness average 100km but it can be up to 250 km thick below continents
Mantle
contains over 82% of the Earth's volume. Solid, rock shelly that extends to a depth of 1800 miles. Composition in the uppermost mantle is peridotite which has a density of 3.3 g/cm3
Richeter Scale
developed by Charles Richter in 1935. Was the first scale developed to describe the magnitude of earthquakes. Determined by measuring the amplitude of the largest wave (typically surface wave) recorded on a seismogram
slab pull
develops as oceanic material sinks into the asthenosphere literally pulling the trialing plate
grabens
elongated valley generated by extensive tensional forces
volcanoes of the deep-ocean basin
erupt a very fluid basaltic lava. Also includes submarine volcanoes that dot the ocean floor including those associated with the mid-ocean ridge system
irregularly distribute on the interiors of continents
erupting material varies from very fluid basaltic lavas to explosive, silica-rich eruptions of granitic magma of Yellowstone. None located in Australia or the eastern 2/3 of the North and South America
Alpine Himalayan belt
extends from the flanks of the Mediterranean Sea past the Himalayan mountains. Results from the collision of the African plane and Eurasia and the Indian plate with southeast Asia. Most faults are thrust or strike-slip faults
flood basalt
flow of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters
laccoliths
form in the same manner as sills, result from more viscous magma resulting in magma collecting as a lens-shaped mass that arches the overlying strata upward. Generally less than a few kilometers wide.
Mesosaurus
fossil only found in Permian shales of eastern south America and southern Africa
oceanic ridge system
frequent but weak seismic activity occurs in this region. Results from tensional forces that occur during seafloor spreading (divergent plates). Most faults are normal faults and transform faults
shield volcanoes
generated from the accumulation of fluid basaltic lavas. Exhibit a broad, slightly domed structure. Most grow from the ocean seafloor to form islands. Do not contain a lot of pyroclastic material. Ex. Mauna Loa and Kilauea
earthquake
ground shaking caused by the sudden and rapid movement of one black of rock slipping past another along fractures in Earth's crust
fault
ground shaking caused by the sudden and rapid movement of one black of rock slipping past another along fractures in Earth's crust
normal fault
if the handling wall moves down relative to the footwall. Has a steep dip of 60degrees usually
reverse fault
if the handling wall moves down relative to the footwall. Has a steep dip of 60degrees usually Reverse fault- dip-slip (primarily vertical movement) in which the hanging wall moves up relative to the footwall. Dip angle of greater than 45 degrees
magnitude
in seismology, the total amount of energy released during an earthquake
batholiths
intrusive bodies (massive) with a surface exposure of more than 100 km^2. Largest intrusive igneous bodies. Discordant and typically several hundred kilometers long and up to 100 km thick.
slab suction
is generated as subduction "sucks" in nearby plates
Panthalassa
large ocean surrounding Pangaea
asthenosphere
lies beneath the lithosphere in the upper mantle (to a depth of 660 km) this layer is relatively soft and weak. Due to certain temperature and pressure conditions, partial melting occurs allowing the lithosphere to move independent of the asthenosphere.
the role of pressure
pressures within the earth increase with depth, melting (which is accompanied by an increase in volume) occur at higher temperatures at depth because of greater confining pressure. When confining pressures drop enough, decompression melting occurs, which can occur when a rock ascends due to convective upwelling moving the rock into zones of lower pressure.
ash and dust
produced when lava contains so many gas bubbles that it resembles a froth, producing very fine glassy fragments
hot spots
provides evidence of the rate and direction of plate movement. These features are areas of volcanism, high heat flow, and crustal uplift that can exceed a few hundred kilometers. This is the surface manifestation of a rising mantle plume.
ridge push
push causes sections of the lithosphere to "slide" down the edges of the ridge
lapili
pyroclasts the sizer of small beads to walnuts (aka cinders)
Crust
relatively thin, rocky outer skin of the earth
thurst fault
reverse faults with a dip angle less than 45 degrees
footwall
rock surface below the fault
body waves
seismic waves that travel through the Earth's interior
surface waves
seismic waves travel along earth's outer layer
S waves
shake the materials it travels through at right angles to their direction of travel. They don't change the volume of materials they pass through, but instead change the shape of the material it passes through. Gases and liquid don't elastically respond to changes in shape. They travel through gases and liquids
sills
tabular plutons formed when magma is injected along sedimentary bedding surfaces (concordant). Horizontal sills are most common, although all orientations exist. Sills closely resemble buried lava flows (both are tabular and exhibit columnar jointing)
ocean drilling
the data collected confirmed that the age of oceanic sediment was the youngest at the oceanic ridge and increased as the distance from the ridge increased.
crater
the depression at the summit of a volcano
brittle deformation
the loss of strength by a material, usually in the form of sudden fracturing
Layering at 660km (layer cake model)
this model describes two zone of convection. It explains why different types of basaltic lava erupt at different locations. However, seismic data indicates that oceanic material descend to a depth greater than 660km
horst
uplifted regions that bound grabens
scoria
vesicular ejecta with a basaltic composition
pumice
vesicular rock with an andesitic or felsic composition
Magma's temperature
when lava cools and begins to solidfy, its mobility decreases and eventually the flow of the lava stops
Transform Fault
where plates grind past each other without the production or destruction of lithosphere
Divergent
where plates move apart, resulting in upwelling of material from the material to create new seafloor
Convergent
where plates move together, resulting in the subduction of oceanic lithosphere into the mantle
