Physical Geography Chapter 14

Wegener postulated what

a massive super-continent, which he Pangaea, existed 225 million years ago and then broke apart into several large sections - the present day continents - that have continued to move away from one another to this day

A divergent boundary is usually represented by

a midocean ridge

Wherever such an oceanic-continental convergent boundary exists, what is formed on land?

a mountain range

Major faults, deeper fault zones can serve as conduits to

allow both water and magma from inside the earth to approach the surface

What is faulting

another prominent result of tectonism, the breaking apart of rock structures, and there is accompanying displacement (movement of the crust on one or both sides of the break)

What kind of rock can occur in folding

any kind of rock

Because plates are relatively cold and rigid, they are also

deformed significantly only at the edges and only where one plate interacts with another

In the 1960's there was a great discovery

depth soundings from the oceans of the world were used to construct a detailed map of ocean floor topography

What happens to the older lithosphere in oceanic trenches?

descends into the asthenosphere in a process called subduction and then recycled

Convergent boundary is sometimes called

destructive boundary

What can be different from different types of volcanic peaks

differences in magma and eruption style

The four principle types of faults are based on

direction and angle of movement

What is columnar basalt?

distinctive, commonly develops from basalt, lava cools uniformly, leaving prominent hexagonal columns - google it, you won't forget it if you see it

Three types of plate boundaries are possible

divergent boundary convergent boundary transform boundary

Very viscous rhyolitic lava

does little more than squeeze out of a vent, bulging up to form a lava dome

Loose, water-saturated sediments, such as coastal landfill may undergo liquefaction, what is this?

during the shaking of the earthquake, the water-saturated material turns fluid, resulting in subsidence, fracturing, and horizontal sliding of the ground surface

Landslides are often triggered by

earthquakes

The surface of relatively recent lava flow tends to be

extremely irregular and fragmented

When magma is expelled onto Earth's surface while still molten, the activity is

extrusive and called volcanism

Most lava comes to the surface through volcano explosions or fissures

fissures

Many of the world's most extensive lava flows were not extruded from volcanic peaks but rather issued from

fissures associated with hot spots

Low silica basaltic lava is associated with shield volcanoes tend to be

fluid and fast

This origination point is known as

focus point

When crustal rocks are subjected to stress, particularly lateral compression, they are often deformed by being bent in the process called

folding

Two types of tectonism

folding and ffaulting

What are detachment faults

form where steeply dipping normal faults tie into low angle (or nearly horizontal) fualts below the surface that develop along the boundary between brittle crustal rocks above and more ductile crustal rocks below

Examples of shield volcanoes

hawaiian islands or tahiti

This new discovery about sea floor spreading means what about Wegener's theory?

he was wrong about one important detail; it is not just the continents that are drifting. The continents are embedded in the thicker lithospheric plates, carried along by the action of seafloor spreading

Why?

nearly all sedimentary strata are initially deposited in a horizontal or near-horizontal attitude - so if they are bent, broken, or tilted, we know that they have clearly experienced tectonism

What happens to the new area above the mantle plume?

new volcanic features develop over the plume, so generating a straight line hot spot trail

Is there technology that can predict an earthquake?

no

Fault scarps are almost always associated with _____ faulting

normal

Four principle faults

normal, reverse, thrust, strike slip

Where are the consequences of tectonic and volcanic activity associated with plate boundaries more vividly displayed?

rim of the Pacific Ocean

When these fill with water they are

sag ponds

Small depressions develop through the settling of rock within the fault zone

sags

From these discoveries, a new theory was proposed by Harry Hess and Robert Dietz that could explain the significance of the midocean ridges, the oceanic trenches, the patterns of the earthquakes and could provide a possible mechanism for Wegener's continental drift. What was this theory?

seafloor spreading

Rocks may be bend or broken in a variety of ways in response to great pressure exerted either in the crust or mantle. This deformation of Earth's crust is called

tectonism or diastrophism

What is continental-continental convergence?

where there is a convergent boundary between two continental plates, no subduction takes place because continental crust is too buoyand (light) to subduct

Where else can divergent boundaries occur?

within a continent

Successive ruptures of a fault line may occur how far apart

years or even centuries

What did they find with ocean floor cores?

sediment thickness and the age of fossils in the sediment increase with increasing distance from the midocean ridges, indicating that sediments farthest from the ridges are oldest

Tectonism results are often conspicuous in the landscape especially in

sedimentary rocks

Transform faults are associated with what kind of activity?

seismic activity, commonly producing shallow focus earthquakes

The energy released in an earthquake moves through the Earth in several different kinds of

seismic waves

Are their tsunami warning systems?

yes, in the Pacific ocean, there are warning systems made up of buoys and sensors that can detect a tsunami midocean and provide advanced warning to endangered coastal populations.

Faulting usually takes place along

zones of weakness in the crust

About 700 million years ago, Rondinia was rifting apart into continental pieces that would eventually fuse back together into

Gondwana (South America, Africa, India, Australia, and Antarctica) and Laurasia (North America and Eurasia)

When magma solidifies below the earth's surface, it produces

plutonic igneous rock

Are lava flows dangerous?

surprisingly, rarely cause loss of life but cause property damage

Why are lava flows usually not dangerous to people?

they are predictable in the paths they take

What controls the nature of a volcanic eruption?

1) the chemistry of the magma that feeds it 2) the relative strength of the surface crust and the degree of confining pressure to which the magma is subjected may also be important 3) the critical chemical component seems to be the relative amount of silica in the magma

What evidence did Wegener have for Continental Drift?

1) the remarkable number of close geologic features on both sides of the Atlantic Ocean and seemed to fit together like puzzle pieces 2) petrologic rock records on both sides of the Atlantic show many distributions - such as ancient coal deposits - that would be continuous if the ocean did not intervene 3) mountain ranges match up 4) paleontology evidence from fossils of some dinosaurs and other reptiles that were found on both side of the Atlantic but no where else in the world 5) fossilized plants are found in similar aged rocks in varying countries, seeds too large and heavy to have been carried across the expanse of the present day oceans by wind\ 6) past climate patterns found in different countries that only made sense if the continents had been together in Pangaea

Why were some scientists still so disbelieving?

1) they believed the Earth's crust to be too rigid to permit such large-scale motions 2) Wegener did not offer a suitable mechanism that could displace such large masses for a long journey

What percentage of all active volcanoes in the world lie within the Pacific Rim?

3/4

Magnitudes are calculated on a logarithmic scale, with an increase from one magnitude to the next of about how many x's?

32

In the US, there are ____ volcanoes that erupted in the last 200 years

50

What is the plate tectonics theory?

A coherent theory of massive lithospheric rearrangement based on the movement of continent sized plates that came on the scene in the late 1960's

This idea of continental drift was revived in the second and third decades of the 20th century by

German meteorologist and geophysicist Alfred Wegener

How is convection connected to plate tectonics?

A very sluggish thermal convection system appears to be operating within the planet, bringing deep-seated hot, lower density rock slowly to the surface. Plates may be pushed away from the midocean ridges to a certain extent, but it appears that much of the motion is the result of the plates being pulled along by the subduction of colder, dense oceanic lithosphere down into the asthensophere. These plates mover slowly over the asthenosphere.

Another kind of hazard associated with earthquakes involves water movements in lakes and oceans

Abrupt crustal movement can set great waves in motion in lakes and reservoirs causing them to overflow shorelines or dams in the same fashion that water can be sloshed out of a dishpan

If current plate movement continues, 50 million years into the future, where will Australia, Africa, East Africa be? What about the Atlantic and Pacific? Southern California?

Australia will straddle the equator as a huge tropical island Africa may close the Mediterranean East Africa may become a new large island like Madaggascar The Atlantic will widen and the Pacific will shrink Southern California will slide past the rest of North America up to the Aleurian Trench in the Gulf of Alaska

Because volcanoes can lie dormant for so long, populations are creeping up around these active volcanoes. What has been done to try to protect the populations?

By the 1970's, a concerted international effort was underway to both assess volcanic hazards and to gain enough knowledge to anticipate the onset of major volcanic eruptions. Looking at past historical eruptions as well as evidence from the geological record to map out the most likely paths of pyroclastic flows and lahars from volcanoes

An example of a tilted fault block mountain range is

California's Sierra Nevada

North America's most famous caldera

Crater Lake

Because the basalt ocean floor is rich in iron, it is magnetized so that the magnetic field within its iron rich grains become aligned with

Earth's magnetic field

So why is the Big Island the only Hawaiian Island active?

It's the only one over the plume

Examples of composite volcanoes

Mt. Fuji, Japan, Mt. Rainier, Washington; Mt. Shasta, California, Mt. Vesuvius, Italy, Mt. St. Helens, Washington

What is asthenosphere convection?

Magma moving up and down like air. Magma on the bottom moves up, cools, and sinks

What are the fastest moving seismic waves and the first to be felt during the quake

P waves or primary waves

About 250 million years ago, Gondwana and Laurasia joined and formed

Pangaea

Examples of Cinder Cone

Paricutin, Mexico, Sunset Crater, Arizona

What is subduction?

Plates moving in. Descent of the edge of the oceanic lithospheric plate under the edge of an adjoining plate

The most commonly quoted magnitude is the

Richter scale

Before Pangaea, there was

Rodinia, an earlier supercontinent

What follows the P waves with a strong side to side and up and down shearing motion and is slower

S waves or secondary waves

Some transform faults extend for great distances. One famous fault system is

San Adreas Fault in Cali

The lithosphere is a mosaic of rigid plates floating over the underlying plastic asthenosphere. These lithospheric plates, consisting of the crust together with the upper mantle, vary considerably in area; some are almost hemispheric in size, whereas others are much smaller. The exact number of plates and some of their boundaries are not completely clear. Continue...

Seven major plates, an equal number of intermediate-sized plates, and perhaps a dozen smaller plates, are recognized. Many of the smaller plates are remnants of once-larger plates that are now being subducted.

What is the Pacific Ring of Fire?

The Ring of Fire is an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean.

Why is this important?

The orientation becomes a permanent record of the polarity of the Earth's magnetic field at the time the rock solidified

What did most scientists think of this idea back then?

They thought it was bullshit

In transform boundaries, when they drift

they break down rocks at the boundaries or depressions

In an earthquake situation, the fault movement allows an abrupt release of energy after

a long slow accumulation of strain

What is oceanic-oceanic convergence?

When the convergent boundary takes place between two oceanic plates, there is subduction. As one of the oceanic plates subducts beneath the other (usually the older plate), an oceanic trench is formed - shallow and deep-focus earthquakes occur and volcanic activity is initiated with volcanoes forming the ocean floor

What is a graben

a block of land bounded by parallel faults in which the block has been downthrown, producing a distinctive structural valley with a straight steep sided fault scarp on either side

Crater Lake was created when

a composite volcano, Mount Mazama erupted and the walls weakened and collapsed as enormous volumes of pyroclastic material were ejected from the volcano. The eruption removed the upper 4000 feet of the peak and produced the caldera. Later the half its depth was filled with water, creating the deepest lakes in North America

The chain of volcanoes that develops in association with the oceanic-continental plate subduction zone is sometimes referred to as

a continental volcanic arc

Volcanoes can look different, but how are most similar?

a crater normally set conspicuously at the apex of the cone

These zones of weakness in the crust is referred to as

a fault zone

Explain the formation of grabens and offset streams?

a graben develops when a block of crust drops down between two parallel faults (most commonly normal faults); an offset stream develops when the course of a stream is displaced by lateral movement along a strike slip fault

The term flood basalt is applied to

a large scale outpouring of basaltic lava that may cover an extensive area of the Earth's surface

The origin of an accreted terrane in a convergent boundary

a moving oceanic plate carries along an old island arc and the oceanic plate begins to subduct under the continental plate, but the island arc is too buoyant for subduction and so is accreted to the continental plate

What is the difference between pyroclastic flow and volcanic mudflow?

a pyroclastic flow is a dense fast moving avalanche of pyroclastics and searing hot gases; a volcanic mudflow is a fast moving mixture of pyroclastics and water, flowing down the volcano with a consistency of wet concrete

Types of folds - syncline

a simple downfold

Types of folds - anticline

a simple symmetrical upfold

Rocks are hard and brittle. If subjected to stresses, they might be expected to break. In nature, when great pressure is applied for long periods of time, particularly in enclosed, heated, buried, subterranean environment, the result if often

a slow plastic deformation that can produce folded structures

What is a terrane?

a small to medium mass of lithosphere - bounded on all sides by faults - that may have been carried a long distance by a moving plate, eventually to converge with the edge of another plate

What is an earthquake

a vibration in Earth produced by shock waves resulting from a sudden displacement along a fault (may also develop from the movement of magma or sudden ground subsidence).

With time, oceanic-oceanic convergence leads to

a volcanic island arc, think hawaii

How can volcanic gases be hazardous?

a volcano emits large quantities of gas during an eruption and included in these gasses are: 1) carbon dioxide 2) sulfur dioxide (mixes with water and forms a mist of sulfuric acid or acid rain which can harm vegetation and cause corrosion, may reflect solar radiation altering global weather) 3) fluorine (kills animals and vegetation) 4) hydrogen sulfide

What else was found during this time?

a world network of seismographs was able to pinpoint the location of every significant earthquake in the world. When locations were mapped, it was clear that earthquakes did not occur randomly but occur in bands, often coinciding with the pattern of the mid-ocean ridge system and oceanic trenches

Why is this?

all developed over the same hot spot, the ancient volcanic remnants of Midway Island are now 1600 miles northwest of the presently active Big Island separated by 27 million years

Intrusions came in what size

all shapes and sizes and compositions

What is volcanism?

all the phenomena connected with the origin and movement of molten rock including the explosive eruptions and the slow solidification of molten material below the surface

What does the modified Mercalli intensity scale do

assigns the strength of local shaking to 1 to 12 categories based on the observed effects and damage

These waves originate where?

at the center of fault motion

Where do fault ruptures take place?

at the surface and displacements can also take place at considerable depth

Lava flows from fissures associated with hot spots is nearly always

basaltic and usually comes in great volume

Two types of igneous intrusions

batholiths and volcanic necks

In a transform boundary, no new crust is created or old ones destroyed, why?

because the plate movement is basically parallel to a transform boundary

Why is this?

because the volcanoes are made up primarily of adesite

Why are convergent boundaries sometimes called destructive boundaries

because they result in removal or compression of the surface crust

So how are midocean ridges and continental rift valleys related?

both are forms of divergent boundaries

Describe and explain the major features associated with oceanic-continental convergence and oceanic-oceanic convergence

both are subduction zones, and so are both associated with shallow and deep focus earthquakes; oceanic-continental subduction produces a deep oceanic trench and a chain of volcanoes just inland from the continental coastline; oceanic-oceanic convergence also produces a deep oceanic trench along with a volcanic island arc parallel to the trench

Because many hot spots seem to be effectively fixed in position for long periods of time, the hot spot trails they produce can indicate

both the direction and speed of plate motion with seamounts becoming progressively older in direction of plate movement

One of the great triumphs of the plate tectonics theory is that it explains

broad topographic patterns like cordilleras (groups of mountain ranges), midocean ridges, oceanic trenches, island arcs, and the associated earthquake and volcanic zones

Shield volcano shape and size

broad, gentle slopes, broader than high

What did most scientists think of Wegener's theory?

bullshit

As pyroclastic flow goes it

burns and bury's everything in its path

When type of volcano is uncommon

calderas

Cinder Cone magma and eruption style

chemistry of magma varies, often basaltic; short life span; pyroclastics ejected from central vent; occasionally produces lava flows

Plates are relatively

cold and rigid

Mudflows or lahars are associated with what kind of volcanoes

composite

Which volcanoes are more likely to erupt explosively

composite volcanoes and lava domes

What is a thrust fault?

compression forces the upthrown block to override the downthrown block at a relatively low angle. Overthrusting occurs frequently in mountain building, resulting in unusual geologic relationships such as older strata being piled on top of younger rocks.

Adjacent to the area the magma has invaded, the country rock usually experiences

contact metamorphism for being exposed to the heat and pressure of the rising intrusion

When this happens you get a

continental rift valley

How does seafloor spreading occur

convection currents bring magma from the asthenosphere up through fissures in the oceanic lithosphere at the midocean ridge. The solidified magma becomes a new portion of ridge along the ocean floor and the two sides of the ridge spread away from each other. Where denser ocean lithosphere converges with less dense continental lithosphere, the oceanic plate slides under the continetal plate in a process called subduction. Magma produced by this subduction rises to form volcanoes and igneous intrusions

The driving mechanism for plate tectonics is thought to be

convection within the Earth's mantle.

In high silica felsic magma

cooler magma; gas bubbles building pressure which is released explosively, generating an eruption in which large quantities of pyroclastic material are ejected

As the magma rises through the plate above, it creates what above ground?

hot spot volcanoes and/or hydrothermal (hot water) features on the surface

The basic theory of plate tectonics can explain tectonic and volcanic activity along the margins of plates, however, there are many places on earth where magma rises from the mantle comes either to or almost to the surface at locations that may not be anywhere near a plate boundary. These locations of volcanic activity in the interior of a plate are referred to as

hot spots

Two additions to plate tectonic theory are

hot spots and accreted terranes

Mafic magma

hotter and more fluid; eruptions have a great outpouring of lava, quietly and without explosions or large quantities of pyroclastic materical

What happens in continental-continental convergence since there is no subduction?

huge mountain ranges are created

Most igneous intrusions have no immediate effect on the surface landscape, but sometimes it does. When?

if the igneous mass is raised high enough to deform the overlying material and change the shape of the surface.

These plutonic igneous rocks form structures called

igneous intrustions

When was the idea of pangea or a supercontinent first arrive?

in the 1590's, geographer Abraham Ortelius and philosopher Francis Bacon in 1620

When magma is solidifies below the surface it is referred to as

intrusive or plutonic activity

Why is the Richter scale not used

it is not ideal for comparing the sizes of very large devised moments magnitude

What is pyroclastic material?

it's the solid rock fragments, solidified lava blobs, and durst that comes out of a volcano during an eruption along with gas and steam

New crust is formed at the oceanic ridges, and within 200 million years, what happens to the crust?

its returned to the mantle by subduction

What is a caldera?

large, steep sided, roughly circular depression resulting from the explosion and/or collapse of a large volcano

Examples of lava dome

lassen peak, california; mono craters, california

Composite volcano structure

layers of lava flows, pyroclastics, and hardened mudflow deposits

Shield volcano structure

layers of solidified lava

Straight line valley that marks the surface position of a fault, especially a strike slope fault, formed by the erosion or settling of crushed rock along the trace of a fault

linear fault trough

Another explanation of volcanic mudflows - just read

loose mantle of ash and pyroclastic flow deposits on the the slopes of a volcano can be mobilized easily by rain or by the melting of snow and glaciers during an eruption. The water mixes with unconsolidated pyroclastic material to produce a fast moving and sometimes hot slurry of mud and boulders, flowing with the consistency of wet concrete

cinder cone structure

loose pyroclastic material; may be composed of ash or cinder-sized pieces

What happens at a divergent boundary?

magma from the asthenosphere wells up in the opening between the plates. This upward flow of molten material produces a line of volcanic vents that spill out basaltic lava onto the ocean floor, with the plutonic rock gabbro solidifying deeper below

Composite volcano magma and eruption style

magma intermediate in chemistry, often andesitic, long life span, both explosive eruptions of pyroclastics and quiet eruptions of lava

Magma and eruption style of shield volcano

magma is usually basaltic, quiet eruptions of fluid lava

With divergent boundary, what happens?

magma wells up from the interior both by eruption from active volcanoes and by flooding out of fissures`

The relative amount of energy released during an earthquake is

magnitude

To explain the existence of hot spots, what model was proposed?

mantle plume

Major flood basalt eruptions in the past have been correlated with

mass extinctions

As subduction takes place, the ocean crust ______, _____underneath increases, and ______ are formed to release the pressure

melts; pressure; volcanoes

What kind of rocks often develop in association with subduction zones

metamorphic rocks

Most transform faults are found along the

midocean ridge system where they form short offsets in the ridge perpendicular to the spreading axis

Because in seafloor spreading midocean ridges are formed by currents of magma rising up from the mantle; volcanic eruptions create new basaltic ocean floor that then spreads away laterally from the ridge, where do we find the newest crust on the planet

midocean ridges

The mantle plume model suggests that

midplate volcanic activity develops over narrow plumes of heated material rising through the mantle - perhaps originating as deep as the core-mantle boundary

The most widely used intensity scale was

modified Mercalli intensity scale

What is being used instead?

moment magnitude

Volcanic necks

more limited than batholiths but prominent. a small, sharpe spire that rises abruptly above the surrounding land. Represents a pipe, or throat, of an old volcano that filled with solidified lava after its final eruptions

Batholiths form the core of many major

mountain ranges

Most basaltic lava flows

move slower than a person can walk

What is movement along the fault zone like?

movement of crust along a fault zone is sometimes slow but it sometimes occurs as a sudden rupture

With this mapping, what was found

narrow deep oceanic trenches and a continuous ridge system that ran across the floors of all oceans and wrapping around the globe like the stitching of a baseball. The mid-Atlantic segment of the midocean ridge system is especially striking, running exactly halfway between the coastlines on both sides, almost as if a giant seam had opened up in the ocean floor between the continents

Where a divergent plate boundary develops within a continent, the resulting downfaulted grabens occasionally extend for extraordinary distances as linear valley enclosed between steep fault scarps. Such lengthy troughs are caleld

rift valleys

What is oceanic-continental convergence?

oceanic crust is denser (made up of dense basaltic crust) than continental crust. Because of this, oceanic lithosphere always goes under continental lithosphere when the two collide. The dense oceanic plate slowly sinks into the asthenosphere in the process of subduction

When there is an oceanic-continental convergent boundary, a mountain range is formed on land and a parallel _____ _____ develops as the seafloor is pulled down by the subducting plate

oceanic trench

What are the three types of convergent boundaries?

oceanic-continental convergence oceanic-oceanic convergence continental-continental convergence

Stream course displaced by lateral movement along a fault

offset stream

The topographic expression of lava flow is

often flat plain or plateau

What happens to the lower density continental lithosphere that cannot be subducted

once its formed, its virtually permanent

What are fault scarps?

one of the prominent topographic features of a fault line, they are steep cliffs that represent the edge of a vertically displaced block

What might the cumulative displacement look like?

over millions of years there could conceivably be hundreds of kilometers horizontally and tens of kilometers vertically

Whether originating from a volcanic crater or a crustal fissure, lava flow spreads outward how?

parallel with the surface over which it is flowing and is maintained as the lava cools and solidifies

Most of the action with plate tectonics takes place where?

plate boundaries

Volcanic activity is associated with

plate boundaries

What has been found all along the Pacific basin?

plate boundaries, primarily subduction zones, along with segments of transform and divergent boundaries

In oceanic-continental convergence, when the subducting slab pulls on the rest of the plate (this is known as slab pulling) this is probably the main cause of most ______ ______, and what happens to the rest of the plate?

plate movement; pulling the rest of the plate in after itself

Convergent boundary

plates collide

What is uniformitarianism?

processes that we see today have always existed on the earth's surface

What is a reverse fault?

produced from compression stresses (pushing together), where the upper block slides up the incline of the fault plane in reverse of the sense of gravity, so that the fault scarp would be severely oversteepened if erosion did not act to smooth the slope

What did Wegener do with this theory?

put together the first comprehensive theory to describe the partially explain the phenomenon of continental drift

The collapse of a lava dome or the rapid subsidence of an eruption column during an explosive eruption of a volcano can lead to a terrifying high speed avalanche of searing hot gases, ash, and rock fragments. This is known as

pyroclastic flow

With a violent explosion, what comes out of the volcano

pyroclastic material and gases can form an eruption column reading up to 10 miles or more. Large fragments of solid rock, called volcanic bombs drop to the ground immediately around the volcano, whereas smaller fragments of volcanic ash and dust form an enormous eruption cloud from which great quantities of ash fall.

What is volcanic mudflows or lahars?

rapid, downslope movement of a dense mixture of weathered rock and water through or within a valley

What is a pluton

refers to intrusive igneous bodies of nearly any size.

The seafloors are like a gigantic conveyor belt, moving ever outward from the midocean ridges toward the trenches. Because of this, oceanic lithosphere has what kind of a lifespan?

relatively short

With the idea of rigid earth theory, what explained reliefs?

result of ancient cooling

What is a normal fault

results from tension stresses (pulling apart or extension) in the crust. It produces a very steeply inclined fault zone, where the upper block slides down the fault plane "normal" to the sense of gravity. A prominent fault scarp is usually formed

Along the margin of a subducting plate, what devleops?

shallow-focus earthquakes at the trench and progressively deeper earthquakes as the subducting plate descends into the asthensophere

Viscosity depends on

silica content

Monitoring of active volcanoes includes measuring

slight changes in the slope of a mountain using sensitive tiltmeters that can detect swelling of a volcano with magma, measuring variations in gas compositions and quantity vented from a volcano that may indicate changes in magma, and monitoring earthquake activity below a volcano - swarms of small earthquakes may indicate the filling of the magma chamber below a volcanic peak. Remote cameras can produce time lapse movie sequences that document changes to lava domes and other crater features.

Cinder Cone shape and size

small, steep-sided

Lava or Plug Dome structure

solidified lava that was thick and viscuous when molten; plug of lava often covered by pyroclastics; frequently occur within the crater of composite volcano

Where does the lava eventually solidify?

some cling to steep slopes but the majority eventually solidify in a horizontal orientation that can resemble the stratification of sedimentary rock

What about tsunami's?

sometimes generated by undersea earthquakes or landslides, move quickly across the ocean, are barely perceptible in deep water, but when they reach shallow water, sometimes build up to heights of 50 feet and crash into the shoreline

Volcanoes with intermediate silica content andesitic magmas erupt

sort of inbetween or do both explosive and fluid eruptions

Pyroclastic flow can travel down a volcano how fast?

speeds more than 100 miles per hour

What are often found along fault lines

springs, sometimes hot water springs

Composite volcano shape and size

steep sided, symmetrical, tall

How does rising magma make room for itself?

stoping - a mining term that refers to ore removal by working upwards. The molten, invading magma can assimilate the surrounding or country rock or heat it enough to make it flow out of the way, or either split or bow it upward

Slight amounts of vertical displacement along ________ faults may also leave a scarp

strike slip

Both thrust faults and reverse faults are commonly associated with

subduction zones and continental collision zones

The Pacific Ring of Fire is also known as

the Adesite Line

What is the most dramatic present day example of a hot spot is

the Hawaiian islands

The volcanoes of the Hawaiian Island chain are progressively younger from west to east, why?

the Pacific Plate is drifting northwestward ward

The most notable area of volcanism is

the Pacific Ring of Fire

The modified Mercalli scale is also used by seismologists to describe what about future earthquakes?

the anticipated intensity of ground shaking that may occur

So what does this mean for the average age of the oceanic crust and continental crust?

the continual recycling of oceanic crust means the average age is only about 100 million yrs old, but the continental crust is 20 x's that. Some of the continental crust has been found to be 4 billion years old

Which mass extinction do they believe may be connected to flood basalt eruptions?

the dinosaurs

Because of the different speeds of P or S waves, what are we able to determine

the distance to an earthquakes focus

The strongest shocks, the greatest crustal vibration, are often felt on the ground directly above the focus, this location is known as

the epicenter

The intersection of that zone with the Earth's surface is called

the fault line

The waves travel out like widening circles gradually diminishing in amplitude with increasing distance from

the focus

The definition of accreted terrane according to notes:

the island crust coming along ocean crust when it converges with a continental crust and is accredted or fused

Batholiths are

the largest and most amorphous intrusion, which is a subterranean igneous body of enormous size and unknown depth. May comprise of dozens of plutons,

What else did they do to prove sea floor spreading?

they drilled holes in the ocean floor. Several thousand ocean floor cores of sea bottom sediments were analyzed

Most of the damage from an earthquake is due to ground shaking. The strength of ground shaking decreases with increasing distance from the epicenter of the earthquake, but this pattern can be significantly modified by

the local geology - loose, unstable regolith, sediments, and soil tend to amplify ground shaking

What is a strike-slip faults?

the movement is horizontal (side to side), with the adjacent blocks being displaced laterally relative to each other. These faults are a consequence of shear stresses (stress causing two parallel surfaces to slide past one another)

If the mantle plumes are permanent, then why do the volcanoes that are formed or other hot spot features move?

the plate above the hot spot is moving, so the features created by the mantle plumes are eventually carried off and become inactive

What is horst?

the relative uplift of a block of land between two parallel faults

The stress that results in tectonism is caused by

the rise of molten material from below, plate movement, or in other cases it may be unrelated directly to plate boundaries

What directly influences the amount of damage that results from an earthquake

the strength of the local ground shaking

What kind of movement along the fault line causes earthquakes

the sudden rupture and displacement along a fault

When the terrane converges with another plate, does it subduct? What happnes?

the terrane is too buoyant to be subducted in the collision and instead is fused or accreted to the other plate and often being fragmented in the process

What theory provided the explanation for this pattern?

the theory of plate tectonics

What is seafloor spreading?

the theory stated that midocean ridges are formed by currents of magma rising up from the mantle; volcanic eruptions create new basaltic ocean floor that then spreads away laterally from the ridge

The farther away from an earthquake, the greater

the time lag between the arrival of the P waves and S waves

Sierra Nevada in California, Idaho's Sawtooth Mountains, and Colorado's Front Range were created at least partially by

the uplift of massive batholiths and are made up of granite or grandodiorite now exposed after the extensive overburden of other rocks eroded away

Shield volcanoes may develop calderas in a different way

they may develop summit calderas when large quantities of fluid lava are vented from rift zones along the sides of a volcano, the magma chamber below the summit can empty and collapse, forming a shallow caldera

Why are the volcanic hazards in the surrounding region of a volcano not always evident?

they may lie dormant for hundreds of years

Are mantle plumes considered permanent? Or do they move?

they seem to be stationary and permanent

In 1963, Vine and Matthews used paleomagnetism to test the theory of sea floor spreading by studying paleomagnetic data from a portion of the midocean ridge system. What did they find?

they were looking for a relatively symmetrical pattern of magnetic orientation, normal polarity, reversed polarity, normal polarity, and so on - both sides of the ridges. This is exactly what they found.

Higher silica lava, such as the andesitic lava associated with the many composite volcanoes around the rim of the Pacific, tends to be

thicker than basaltic lava, usually moving only short distances down the slopes of the volcano

In many cases, igneous intrusions are exposed at the surface how?

through the action of the external processes, often becoming conspicuous because they are usually resistant to erosion and with the passage of time stand up relatively higher than the surrounding land

Both waves travel

through the body of Earth

What is a transform boundary?

two plates slip past one another laterally along great vertical fractures called transform faults (a type of strike-slip fault)

What is a divergent boundary?

two plates that may diverge from one another

What are surface waves

typically arrive immediately after the S waves and produce strong side to side movement as well as the up and down rolling motion often experienced during a large earthquake

Tilted fault block mountain range

under extensional stresses, a surface block may be faulted along one side without any faulting or uplift on the other. When this happens, the block is tilted asymmetrically, producing a steep slope along the fault scarp and a relatively gentle slope on the other side of the block

Volcanic islands carried off the hot spot may eventually subside to form _______ ________ as the oceanic lithosphere cools and becomes denser

underwater seamounts

What is the rigid Earth theory?

until the mid 20th century, most Earth scientists assumed that the planets crust was static or fixed and changed only by sea level and periods of mountain building

Lava or Plug Dome magma and eruptions style

usually high in silica, often rhyolitic; dome grows by expansion of viscuous lava from within; explosive eruptions

Lava or Plug Dome shape and size

usually smaller, irregular in shape

In faulting, the displacement can be

vertical or horizontal or both

Speed and distance of lava flow depends on

viscosity (how thick and sticky it is)

What about volcanic activity and fault zones

volcanic activity is also associated with fault zones as magma forces its way upward in the zone of weakness

What are surface expressions of subsurface igneous activity?

volcanoes

What develops from magma generated in the subduction zone?

volcanoes

With convergent boundaries, what happens?

volcanoes are formed in association with the generation of magma

Which volcanoes are more intermediate

volcanoes associated with subduction zones