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