Ch. 5 Volcanoes and Volcanic Hazards
Volcanic arcs can be constructed on oceanic as well as continental lithosphere. Those that develop within the ocean and grow large enough for their tops to rise above the surface are labeled ______ in most atlases.
Archipelagos
The volcanoes of the Cascade Range in the northwestern United States, included 1. 2. 3.
Are examples of volcanoes generated along a convergent plate boundary 1. Mount Hood 2. Mount Rainier 3. Mount Shasta
As the thick lava is squeezed out of a vent, it often produces a dome-shaped mass called a ___ __.
Lava dome
1902 pyroclastic flow and associated surge from Mount Pelee', a small volcano on the Caribean island of ____________________, destroyed the port town of St. Pierre.
Martinique
From its base on the Pacific Ocean to its summit, ______________ Loa is over 6 miles high, exceeding the elevation of Mt. Everest
Mauna
After sufficient quantity of the rock has melted, blobs of buoyant magma slowly __________ __________.
Migrate upward.
On exception is the cinder cone in _____________, which has erupted more than _____ times since it formed in 1850.
Nicaragua 20
Because this newly formed magma is less dense than the mantle rock from which it was derived, it rises and collects in reservoirs located just below the ridge crest.
This activity continuously adds new basaltic rock to plate margins, temporarily welding them together, only to have them break again as spreading continues.
Composition
another factor influencing volcanic behavior is the composition
For two weeks prior to the first eruption, numerous Earth tremors caused ___________________ in the nearby village of _____________.
apprehension Paricutin
Cinder cones
are built from ejected fragments that begin to harden in flight to produce the vesicular rock scoria
ash and dust
are produced when gas-rich viscous magma erupts explosively
Below the ridge axis where lithospheric plates are continually being pulled apart, the solid yet mobile mantle responds by _____________ to fill the rift.
ascending
The gas-laden magmas that migrate through pipes travel rapidly enough to undergo minimal alteration during their _______.
ascent
When magmas with intermediate (andesitic) or felsic (rhyolitic) compositions erupt explosively, they emit ______________ and the vesicular rock ________________.
ash pumice
Caldera-forming eruptions are of colossal proportions, ejecting huge volumes of pyroclastic materials, mainly in the form of
ash and pumice fragments These materials form pyroclastic flows that sweep across the landscape, destroying most living things in their paths. Upon coming to rest, the hot fragments of ash and pumice fuse together, formed a welded tuff and closely resembles a solidified lava flow. Despite the immense size of these calderas, the eruptions that cause them are brief, lasting hours to perhaps a few days.
Volcanic eruptions can eject dust-sized particles of volcanic ash and sulfur dioxide gas high into atmosphere
ash particles reflect solar energy back to space, producing temporary atmospheric cooling
The pyroclastic fragments range in size from fine ________ to _________________ that may exceed 3 meters in diameter.
ash to bombs
Based on the extraordinary volume of erupted material, researchers have determined that the magma chambers
associated with Yellowstone-type calderas must be similarly monstrous As more and more magma accumulates, the pressure within the magma chamber begins to exceed the pressure exerted by the weight of the overlying rocks An eruption occurs when the gas-rich magma raises the overlying crust to create vertical fractures that extend to the surface. Magma surges upward along these cracks, forming a ring-shaped eruption. With a loss of support, the roof of the magma chamber collapses.
Eruption colums can rise 25 miles into the ________________.
atmosphere
The composition of volcanic gases is important because these gases contribute significantly to our planet's ______________.
atmosphere
Due to the extreme nature of the eruption required to produce the large ______ provinces, some researchers believe the eruptions were responsible for the extinction of many of Earth's life-forms.
basalt
Partial melting of mantle rock at spreading centers produces _______________ magma.
basaltic
Recall that the partial melting of mantle rock (peridotite) generates magma having a ___________ composition.
basaltic
Shield volcanoes owe their shape to fluid __________________ lavas.
basaltic
The pyroclastic material tends to have _______________ composition.
basaltic
Vast majority of lava of Earth is _________ in composition. 90%
basaltic
Extensive study of the hawaiian islands revealed that they are constructed of a myriad of thin _______________ lava flows averaging a few meters thick, intermixed with relatively _______________ amounts of pyroclastic ejected material
basaltic minor
How can we detect this event?
because the summit of the volcano begins to inflate and rise months or even years before an eruption
Their upper surface consists largely of massive, detached blocks, hence the name _____________ ___________.
block lava Similar to aa flows, these lavas consist if blocks with slightly curved, smooth surfaces, rather than the rough, sharp, spiny surfaces typically of aa flows
particles larger than 64 millimeters in diameter are called ______________ when they are made of hardened lava
blocks
As magma rises, the confining pressure is reduced, causing the dissolved gases to separate from the melt to form tiny __________.
bubbles
Because silica-rich magmas are sticky (viscous) a significant portion of the gaseous material remains dissolved until the magma nears Earth's surface, at which time tiny _____________ begin to form and grow.
bubbles
Calderas
caldaria = cooking pot large steep-sided depressins with diameters that exceed .6 miles and have a circular form those less than 1 kilometer across are called collapse pits or craters
A _______________________ usually forms when the roof of solid rock above a magma chamber collapses.
caldera
Another feature to many active shield volcanoes is a large , steep - walled ________________________, that occupies the summit.
caldera
Ash and pyroclastic material
can collapse roofs of buildings drawn into lungs of humans/animals get into aircraft engines emit gases, sulfur dioxide which affects air quality and when mixed with rainwater, may destroy vegetation and reduce the quality of ground water
Mt. Rainier, Washington
most dangerous volcano because like Nevado del Ruiz, it has thick, year-round mantle of snow and glacial ice 10,000 people live in the valleys around Rainer future rain could produce lahars that could be similarly destructive
When a volcano becomes inactive, congealed magma often becomes preserved in the feeding _______________ of the volcano as a crudely cylindrical mass.
conduit
Most volcanic eruptions are fed lava through __________ that connect shallow magma chambers to vents located at the surface.
conduits
The most widely recognized volcanic structures are the
cone-shaped edifices of composite volcanoes that dot Earth's surface
Explosive discharges continued, throwing hot fragments and ash occasionally as high as 20,000 feet into the air. Larger fragments fell near the ____________, some remaining incandescent as they rolled down the slope.
crater
In addition, a cinder cone has a quite large, deep ______________ in relation to the overall size of the structure.
crater
Other craters form during explosive eruptions as the rapidly ejected particles erode the _____________ walls.
crater
Volcanoes built primarily of pyroclastic materials typically have _____________that form by gradual accumulation of volcanic debris on the surrounding rim.
craters
Heat from the hot magma is often sufficient to partially melt the overlying _____________ rocks, generating a less dense, silica rich magma, which continues the journey toward's Earth's surface.
crustal
The first discharge began along a 4 mile fissure where 100 meter high ____________ of ______________ formed as red-hot lava was ejected skyward.
curtain of fire
1 large eruption every ______________.
decade
In 1980, May 18, 1980, the largest volcanic eruption to occur in North America in historic times transformed a picturesque volcanoe into a _________________ remnant
decapitated
Much of Earth's volcanic activity occurs along oceanic ridges or _______________- boundaries
divergent
Although relatively symmetrical, some cinder cones are elongated and higher on the side that was ______________ during the final eruptive phase.
downwind
When gravity overcomes the initial upward thrust provided by the escaping gases, the _____________ materials begin to fall, sending massive amounts of incandescent blocks, ash, and ________________ cascading downslope.
ejected pumice
Southwestern Washington State, Mount Saint Helens ________________ with tremendous force.
erupted
lava
erupted magma
Composite cones are noted for generating _______________________ eruptions that eject huge pyroclastic material.
explosive
Gases also give magmas their ________________ character.
explosive
The greatest volume of volcanic material is extruded from fractures in Earth's crust called ___________.
fissures
Mafic (basaltic) laves, which contain less silica are relatively ____________________and travel 90 miles before solidifying.
fluid
However, many composite cones also emit various amounts of __________ basaltic lava and occasionally, ___________________ material having felsic (rhyolitic) compositon.
fluid pyroclastic
The flanks of Mauna Loa have gentle slopes of only a few degrees. This low angle results cause very hot, ____________ lava traveled fast an far from the _____________.
fluid vent
Water dissolved in magma tends to increase _________________- because it reduces formation of long silicate chains by breaking silicon-oxygen bonds
fluidity
Volcanic activity frequently begins when a fissue (crack) develops in Earth's crust, as magma moves ____________ up through a fissue, its path is usually localized into a circular _______________ that terminates at a surface opening called a ________________.
forcefully conduit vent
pillow lavas
form on the ocean floor and have elongated shapes, resembling toothpaste coming out of a tube
Kilauea's caldera
formed by gradual subsidence as magma slowly drained laterally from the underlying magma chamber, leaving the summit unsupported
At the other extreme, highly viscous magmas expel particles of ____________________ lava and gases at supersonic speeds, creating buoyant plumes called _________________ _______________.
fragmented lava eruption columns
Many of these vents emit only gases and are called _______________.
fumaroles
Pyroclastic flows are also called ______________ _________________. These fiery flows are capable of racing down steep volcanic slopes at speeds that exceed 60 miles per hour.
nuee' ardentes (glowing avalanches)
Lava has been intermittently pouring into the ______________________ever since, added new land to the island of _________________.
ocean Hawaii
Most active volcanoes on land are located along the margins of the _____ _____--notably within the _______ ________________ _____________known as the ___ ___ ____
ocean basins Circum-Pacific Belt "Ring of Fire"
1500 of Earth's known volcanoes have erupted at least _______________, and some several times, in the past 10,000 years.
once
Here, smooth-surfaced ________________ lava formed a lava lake.
pahoehoe
Others are ___________________ cones that are found on the flanks or within the calderas of larger volcanic structures.
parasitic
As a volcano matures, material also tends to be emitted from fissures that develop along the flanks or at the base of the volcano. Continued activity from a flank eruption may produce one or more small _____ cones.
parasitic cones
Most magma is generated by _________________ ____________- of the the rock in the upper mantle and has a basaltic composition.
partial melting
Then, on February 20, sulfurous _________ began billowing from a small depression that had been in the cornfield for as long as local residents could remember.
gases
When fluid basaltic magma erupt, the pressurized _____________ readily escape.
gases
Each event was followed by nearly a month of ____________________________.
inactivity
One rare type of conduit, called a ________, carries magma that originated in the mantle at depths that may exceed 93 miles.
pipe
The basic connection between plate tectonics and volcanism is that ___
plate motions provide the mechanisms by which mantle rocks undergo partial melting to generate magma
Volcanic necks are also called ________________.
plugs
Powerful hot blasts that carry small amounts of ash separate from the main body of a _____________________ flow.
pyroclastic
Pyroclastic flows may originate in a variety of volcanic settings. Some occur when a powerful eruption blasts _________________ material out of the side of a volcano.
pyroclastic
Some of the most destructive forces of nature are ____________ _____________, which consist of hot gases infused with incandescent ash and large lava fragments.
pyroclastic flows
When volcanoes erupt energetically, they eject pulverized rock, lava, and glass fragments from the vent. The particles produced are called ________________ ______________.
pyroclastic materials
Andesites and other lavas of intermediate composition account for most of the ________.
rest
pumice
is lighter in color and less dense than scoria, and many pumice fragments have so many vesicles that they are light enough to float
scoria
is the name applied to vesicular ejecta that is a product of basaltic magma These black to reddish brown fragments are generally found in the size range of lapilli and resemble cinders and clinkers produced by furnaces used to smelt iron.
Most rhyolitic lavas seldom travel more than a few ____________ from their vents.
kilometers
In addition to violent eruptions, large composite cones may generate a type of fluid mudflow referred to by its Indonesian name, ________________.
lahar
lapilli
larger pyroclasts that range in size from small beads to walnuts; they are also called cinders
and bombs, when they are ejected as incandescent _____________
lava
Because cinder cones are composed of loose fragments rather than solid rock, the ___________ usually flows out from the uncosolidated base of the _______ rather than from the crater.
lava cone
pahoehoe flows often dvelop cave-like tunnels called ________ _________, that were previously conduits for carrying lava from an active vent to the flow's leading edge
lava tubes
In continental settings, the density of crustal rocks is ____________- than that of the ascending material, causing the __________ to pond at the crust-mantle boundary.
less magma
crater
located at the summit of most volcanic cones is a somewhat funnel-shaped depression
Cinder cones are composed mostly of ______ scoria fragments, some produce extensive lava fields.
loose
The gaseous components in magma, mainly dissolved water, also affect the mobility of ________________
magma
viscosity
magma's mobility
Along certain convergent plate boundaries, two plates move toward each other, and a slab of oceanic lithosphere descends into the ____, generating a _______________________.
mantle deep - ocean trench
Occasionally, these expanding gases propel incadescent lava hundreds of ____________ into the air, producing lava fountains.
meters
In addition, swelling of the magma chamber fractures the rock above, allowing the fluid magma to move upward along the newly formed openings often generating outpourings of lava for weeks, _____________ or years
months
Loss of gases renders magma (lava) ____________ viscous.
more
Cinder cones are also called
scoria cones
This most commonly occurs on the ocean floor in association with _________________________ spreading.
seafloor
Most shield volcanoes begin on the ocean floor as _________________, a few of which grow large enough to form volcanic islands
seamounts
lava tubes
serve as insulated pathways that facilitate the advance of lava great distances from its source, therefore lava tubes are important features of fluid lava flows
The particles range in size from very fine dust and sand-sized volcanic ash to pieces that weigh ____________ ________________.
several tons
A _____________________-volcano is produced by the accumulation of fluid basaltic lavas and exhibit the shape of a broad, slightly domed structure that resembles a warrior's shield.
shield
Hot basaltic lavas, which are usually very fluid, generally flow in thin, broad sheets or ________________ ribbons.
streamlike
_____________compounds are easily recognized by their pungent odor.
sulfur
Volcanoes are natural sources of pollution; some emit ______________________, which combines with atmospheric gases to form sulfuric acid and other sulfate compounds
sulfur dioxide
Astronomers are so certain the Mauna Kea is over the hill that they built an elaborate observatory on its ______________, housing expensive teloscopes.
summit
Craters also form when the ______________ area of a volcano collapses following an eruption.
summit
The newly formed magma, which is less dense than surrounding rock, slowly rises toward the ____________________.
surface
vent in volcano
surface opening
These low-density clouds called ____________ can be deadly but seldon have sufficient force to destroy buildings in their path.
surges
pyroclastic materials are also called _________
tephra
volcanic cone
the cone-shaped structure we call a __ __ is often created by successive eruptions of lava, pyroclastic material, or combination of both
The magma generated in the mantle may change from a fluid basaltic magma to a silica rich andesitic or rhyolitic magma as it moves up through ____
the continental crust
The more viscous the material
the greater its resistance to flow ex: syrup is more viscous than water
magma
the source material for volcanic eruptions is _______, molten rock that usually contains some crystals and varying amounts of dissolved gas
2010, eruption of Iceland's Eyjafjallajokull Volcano, sent high ash into the atmosphere
the thick plume of ash drifted into Europe causing airlines to cancel thousands of flights, leaving hundreds of thousands of travelers stranded.
The lava flows generally form in the final stages of the ___________________ life span, when the magma body has lost most of its gas content.
volcano's
these destructive sea waves sometimes result from powerful volcanic explosions or the sudden collapse of flanks of _________________ into the ocean.
volcanoes 1883, volcanic eruption on the Indonesian island krakatoa tore the island apart and generated a tsunami that killed 36,000
At temps that exceed 2000 F, these gases can quickly expand to occupy hundreds of times their original ______________________.
volumes
lahars occur when volcanic ash and debris becomes saturated with ____________ and rapidly moves down steep volcanic slopes, generally following stream valleys.
water 1. Mt. St. Helens 2. 1985, deadly lahars during eruption of Nevado del Ruiz in the Andes mountains of columbia claimed 25,000 lives
When hot ash falls, the glassy shards often fuse to form a rock called ____________ __________.
welded tuff Sheets of this material as well as ash deposits that later consolidate, cover vast portions of the western United States
70 volcanoes expected each
year
Mount Pelee'
image
Mt. Etna in Italy
image
The Destruction of Pompeii
image
Wizard Island
image
Yellowstone - type calderas
image
blocks volcano
image
bombs in volcano
image
fumaroles
image
geysers
image
hot springs
image
pumice
image
pyroclastic flow
image
pyroclastic flows
image
surges in volcanoes
image
scoria
image of scoria
Yellowstone National park
image of the park
All magma contain some water vapor and other gases that are kept in solution by the ___________________________ pressure of the overlying rock.
immense
Stromboli is well known for eruptions that eject incandescent blobs of lava that it has been referred to as the __________ of the ______________.
"Lighthouse of the Mediterranean"
2. Hawaiian-Type Caldera
-unlike Crater Lake-type calderas, many calderas form gradually because of the loss of lava from a shallow magma chamber underlying the volcano's summit Hawaii's active shield volcano, Mauna Loa and Kilauea, both have calderas at their summits
Rhyolitic (felsic) flows make up ____%
1
In one study, half of all cinder cones examined were constructed in less than ___ month.
1 month and 95% were formed in less than 1 year..
The gaseous portion of most magmas makes up ______%
1 to 6 %
Destruction of Pompeii
1. A.D. 79 eruption of Italian volcano we now called Mount Vesuvius 2. entire city of Pompeii near Naples and few thousand of its residents were entombed beneath a layer of volcanic ash and pumice that fell like rain
Example of several young volcanic island arcs border the western Pacific basin, including the 1. 2. 3.
1. Aleutians 2. Tongas 3. Marianas
Other examples of large calderas located in the United States
1. California's Long Valley Caldera 2. LaGarita Caldera, located in San Juan Mountains of southern Colorada 3. Valles Caldera west of Los Alamos, New Mexico These and similar calderas elsewhere around the globe are among the largest volcanic structures on Earth, hence the name "supervolcanoes". Volcanologists have compared their destructive force with that of the impact of a small asteroid
Examples of shield volcanoes 1. 2. 3.
1. Canary Islands 2. Hawaiian Islands 3. Galapagos 4. Easter islands
The volcanic structures comprise most of the islands of the deep-ocean basins, including the
1. Hawaiian Islands 2. Galapagos islands 3. Easter Island
Large calderas tend to exhibit a complex eruptive history.
1. In the Yellowstone region, for example, three caldera-forming episodes are known to have occurred over the past 2.1 million years. 2. The most recent event 630,000 years ago, was followed by episodic outpourings of degassed rhyolitic and basaltic lavas. 3. Geologic evidence suggests that a magma reservoir still exists beneath Yellowstone; thus another caldera-forming eruption is likely but not necessarily imminent
Most calderas are formed by one of the following processes 1. 2. 3.
1. collapse of the summit of a large composite volcano following an explosive eruption of silica rich pumice and ash fragments (Crater Lake - type calderas) 2. collapse of the top of a shield volcano caused by subterranean drainage from a central magma chamber (Hawaiian-type calderas) 3. collapse of a large area, caused by the discharge of colossal volumes of silica rich pumice and ash along ring fractures (Yellowstone - type calderas
Volcanoes extrude 1. 2. 3.
1. lava 2. large volumes of gas 3. pyroclastic material: broken rock, lava, bombs, fine ash, and dust
Pyroclastic flows are composed of two parts: 1. 2.
1. low density cloud of hot expanding gases containing fine ash particles 2. ground-hugging portion that is often composed of pumice and other vesicular pyroclastic material
Other eruptions that have produced significant effects on climate worldwide include: 1. Indonesia Mount Tambora in 1815 2. eruption of El Chichon in Mexico in 1982
1. produced the year without a summer (1816) 2. The eruption for El Chichon, although small, emitted an unusually large quantity of sulfur dioxide that reacted with water vapor in the atmosphere to produce a dense cloud of tiny sulfuric acid droplets. These particles, called aerosols, take several years to settle out of the atmosphere. Like fine ash, these aerosols lower the mean temperature of the atmosphere by reflecting solar radiation back to space
Characteristic of large caldera-forming eruptions
1. slow upheaval of the floor of the caldera that produce a central elevated region called a resurgent dome 2. Unlike calderas associated with shield volcanoes or composite cones, Yellowstone-type depressions are so large and poorly defined that many remained undetected until high -quality aerial and satellite images became available.
The primary factors that affect the behavior of magma and lava are 1. 2. 3. These factors determine a magma's mobility or viscosity.
1. temperature and composition 2. amount of dissolved gases
Other sites of intraplate volcanisms meaning Within the plate include large outpourings of fluid basaltic lavas like those that compose : 1. 2. 3. 4.
1. the Columbia River basalts, 2. the Siberian Traps in Russia 3. India's Deccan Plateau 4. Several large oceanic plateaus including the Ontong Java Plateau located in the western Pacific (These massive structures are estimated to be 6 - 25 miles thick.
Mount Saint Helens
1. trees within a 400 km area lay intertwined and flattened 2. mudflows carried ash, trees, and water and saturated rocks debris 29 kilometers down the Toutle River 3. 59 dead 4. some suffocated from cloud of ash and gases 5.
In June 1944, a clinker aa flow ______________ meters thick moved over much of the village of ________________________________, leaving only the church steeple exposed.
10 meters or 30 feet thick San Juan Parangaricutiro
These flows destroyed nearly ____homes, covered a major roadway, and eventually reached the ______.
100 rural homes sea
In the first day, the cone grew to __________ feet and by the fifth day it was more than 330 feet high.
130
______% carbon dioxide
15%
The longest and largest rift eruption ever recorded on Kilauea began in ______ and continues to this day.
1983
Mount Etna, on the other hand has erupted once every ______________ years since 1979
2
Mt. Etna in Italy has more than _____ secondary vents, some of which have built parasitic cones.
200
Paricutin is located about ______ miles west of Mexico City.
200 miles
As a result of this short life span, cinder cones are small, usually between 100 feet and 1000 feet. A few rare examples exceed ______________ feet in height.
2100.
Nearly all of St. Pierre's __________________ inhabitants were killed. Only ___person on the outskirts of town --a prisoner protected in a dungeon and a few people on _______________ in the harbor were spared.
28,000 1 ships
1902 eruption of Mount Pelee' killed
28,000 people wiping out the entire population of nearby city of Saint Pierre
One of the most destructive volcanic events, called the Laki eruptions began along a large fissure in southern Iceland in 1783.
3.4 cubic miles of fluid basaltic lavas 130 million tons of sulfur dioxide and other poisonous gases were released when sulfur dioxide is inhaled, it reacts with moisture in lungs to make sulfuric acid. this eruption's sulfur dioxide release cause the death of more than 50 percent of Iceland's livestock crop failure in parts of Western Europe thousands died from lung-related diseases a recent report estimates that a similar eruption today would cause more than 140,000 cardiopulmonary fatalities in Europe alone
The eruption of Kilauea that began in 1983 has been ongoing for more than ___ years
30
________%sulfur dioxide
5%
__________% nitrogen
5%
More than ______ eruptions have been witnessed here since 1823
50
Magmas that produce mafic rocks such as basalt contain _____ silica
50 %
Kilauea's measures 2 by 3 miles and is ___________________deep. The walls of this caldera are almost vertical and as a result, it looks like a vast, nearly flat-bottomed pit.
500 feet
Intermediate rock types, like andesite and diorite produce magma with ____ silica
60 %
The greatest volume of magma (____%) is produced along the oceanic ridge system in association with seafloor spreading.
60 %
Magmas that produce felsic: granite and its extrusive equivalent, rhyolite contains more than _____ silica
70 %
_______%water vapor
70%
After __________________ years of intermittent pyroclastic explosions and nearly continuous discharge of lava from its vents at its base, the activity ceased almost as quickly as it had begun.
9
Lava domes are usually only a few tens of meters high, and they come in a variety of shapes that range from pancake-like flows to a steep-sided plugs that were pushed upward like pistons. Most lava domes grow over a period of several years, following an explosive eruption of silica-rich magma.
A recent event is the dome that began to grow in the crater of Mount St. Helens immediately following the 1980 eruption.
This active zone consists in part of a chain of continental volcanoes that are distributed along the west coast of the _______________.
Americas, including the large cones of the Andes in South America and the Cascade Range of the western United States and Canada.
All volcanoes succumb to forces of _______________ and ________________. Weathering and erosion.
As erosion progresses, the rock occupying the volcanic conduit, which is often highly resistant to weathering, may remain standing above the surrounding terrain long after the cone has been worn away.
Temperature
As lava cools and begins to congeal, its viscosity increases and eventually the flow halts
Hence, a mantle -derived magma changes chemically as it rises by assimilating silica - rich crustal rocks.
At the same time, extensive magmatic differentiation occurs, which means formation of secondary magma from parent magma.
Another group of volcanoes are the Seamounts that form along the crest of the mid-ocean ridges.
At these depths of 1 - 3 km below sea level, the pressures are so intense that the gases emitted quickly dissolve in the seawater and never reach the surface.
Most of the recent activity on Kilauea has occurred along the flanks of the volcano, in a region called the _____ ____ _______,.
East Rift Zone
Extraordinary amounts of lava have been extruded along fissures in a relatively short time. The voluminous accumulations are commonly referred to as __________ _______________ because most have a ________________ __________ and tend to be rather flat and broad.
Basalt plateaus Basaltic composition
The ________________ Plateau located in northwestern United States, which consists of the Columbia River basalts, is the product of this type of activity.
Columbia Plateau
Earth's most picturesque yet dangerous volcanoes are _________________________ ____________________
Composite volcanoes, also known as stratovolcanoes
The first lava flow came from a fissure that opened just north of the ______________________________________.
Cone, but after a few months, flows began to emerge from the base of the cone.
As hot rock rises, it experiences a decrease in _______________ pressure and undergoes melting without the addition of heat. This process is called decompression melting.
Confining
The volcanic activity on Kilauea began along a series of fissures in the ____________ __ ___.
East Rift Zone
Volcanism associated with convergent plate boundaries may also develop where slabs of oceanic lithosphere are subducted under continental lithosphere to produce___ __ ___ .
Continental volcanic arc
Although the depth at which mantle plumes originate is a topic of debate, some appear to form deep within Earth, at the ____ ___ boundary.
Core-mantle boundary
1. Crater Lake- Type Calderas
Crater Lake, Oregon, is situated in a caldera 6 miles wide and 3800 feet deep. formed 7,000 years ago composite cone, named Mount Mazama, extruded 12 to 17 cubic miles of pyroclastic material 1500 meters of the summit of this prominent cone collpased, producing a caldera that filled with rainwater Later, volcanic activity produced a small cinder cone called Wizard Island, provides a mute reminder of past activity
When the head of a superplume reaches the base of the lithosphere, _______________ melting progresses rapidly.
Decompression
The rocks filling these pipes originated at great _______, where pressure is sufficiently high to generate ________________ and other high pressure minerals.
Depth Diamonds
In 1943, its eruptive phase began, in a cornfield owned by _______________ who witnessed the event as he prepared the field for planting.
Dionisio Pulido
Italy's Etna and Stromboli
Display very persistent eruption activity, and molten lava has been observed in their summit craters for decades.
1783 eruption in Iceland, the atmospheric circulation around the globe appears to have been affected.
Drought in the Nile River valley and in India winter of 1784 brought the longest period of below zero temperatures in New England's history
Volcanic ash and aviation
During the 15 year, 80 jets have been damaged in flying into clouds of volcanic ash 1989 Boeing 747 carrying more than 300 people encountered an ash cloud from Alaska's Redoubt Volcano, engines stalled but were able to restart and land in Anchorage
Geologists consider pipes to be windows into ____________________ that allow us to view rocks that normally form only at great depths.
Earth
Although most spreading centers are located along the axis of an oceanic ridge, some are not. In particular, the __________ _____ ____ is a site where continental lithosphere is being pulled apart.
East African Rift Vast outpourings of fluid basaltic lavas as well as several active composite volcanoes are found in this region of the globe.
The process of transporting essentially unaltered magma though 93 miles of solid rock is _____________ and accounts for the scarcity of natural diamonds.
Exceptional
Rather than build cones, ______________ ____________________ usually emit fluid basaltic lavas that blanket wide areas.
Fissure eruptions
Numerous fissures eruptions have buried the landscape, creating a lava plateau nearly 1 mile thick. Some of the lava remained molten long enough to flow 90 miles from its source. The term _____________ ____________ describe these extrusions. Lava Domes
Flood basalts
Why do eruptions occur in the interiors of plates?
Hawaii's Kilauea, one of the world's most active volcanoes, is situated thousands of kilometers from the nearest plate boundary, in the middle of the vast Pacific plate.
fluid basaltic magmas tend to generate two types of lava flows known by ________________ names.
Hawaiian names
Along some ridge segments, outpourings of pillow lavas build numerous volcanic structures, the largest of which is _________
Iceland
500 million people from ___________ and ____________ to Italy and oregon live near active volcanoes. They face a number of volcanic hazards, such as pyroclastic flows, lahars, lava flows, falling volcanic ash, and volcanic gases.
Japan and Indonesia
bombs 6 meters and weighing 200 tons were blows 600 meters from the vent during an eruption of the ____ ___ ____
Japanese volcano Asama
Eruptions that involve very fluid basaltic lavas, such as the eruptions of _____________-- on Hawaii's Big Island, are often triggered by the arrival of a new batch of molten rock into a near - surface magma chamber.
Kilauea
Several months before each eruptive phase, _______________________inflates as magma gradually migrates upward and accumulates in a central reservoir located a few kilometers below the summit.
Kilauea
__________________ the most active and intensively studied shield volcano in the world, is located on the island of ___________________ in the shadow of Mauna Loa.
Kilauea Hawaii
The best known volcanic pipes are the diamond bearing -__________pipes of South Africa.
Kimberlite
Composite cones are ______________, nearly symmetrical structures consisting of alternating layers of explosively erupted ___________________ and ______________ interbedded with lava flows.
Large Cinders and ash
It is thought that most intraplate volcanism occurs where a mass of hotter than normal mantle material called a ___________ _____
Mantle plume assends toward the surface.
Figure 5.2 Douglas fir trees snapped off or uprooted by the lateral blast of
Mount St. Helens
Some shield volcanoes form on continental crust 1. 2.
Nyamuragira, Africa most active volcano Newberry Volcano, Oregon
Over time, the cooler outer layer of the dome may start to crumble, producing relatively small pyroclastic flows consisting of dense blocks of lava.
Occasionally, the rapid removal of the outer layer causes a significant decrease in pressure on the hot gaseous magma in the interior of the dome.
The Ring of fire, a belt of explosive volcanoes, surrounds the ___ basin.
Pacific
The Ring of Fire exists because oceanic lithosphere is being subducted beneath most of the landmasses that surround the ____ _____.
Pacific Ocean
One of the very few volcanoes studied by geologists from its very beginning is the cinder cone called _____________.
Paricutin
These built an aesthetically pleasing cone, while fine ash fell over a much larger area, burning and eventually covering the village of ___________.
Paricutin
Today, __________________ is just one of the scores of cinder cones dotting the landscape in this region of ___________________.
Paricutin Mexico Like the others, it will not erupt again.
When the activity became localized, a cinder and spatter cone, given the Hawaiian name ____ __, was built.
Puu Oo
Explosive degassing of the interior magma triggers a fiery _____________ flow that races down the flanks of the volcano.
Pyroclastic
Most are located in a relatively narrow zone that rims the Pacific Ocean, called the ___ _____ ___.
Ring of Fire
These plumes of solid yet mobile rock _______toward the surface in a manner similar to the blobs that form within a lava lamp.
Rise
Although the main pyroclastic flow was largely confined to the valley of ___________________ Blanche, a low-density fiery __________________ spread south of the river and quickly engulfed the entire city.
Riviere Blanche surge
____________, New Mexico, is a widely recognized and spectacular example of these structures geologists call ______ ____ or plugs.
Shiprock Volcanic necks or plugs
calderas
Some volcanoes have very large circular depressions called _____ that have diameters greater than .6 miles and in some cases exceed 30 miles
Since 1995, pyroclastic flows generated by the collapse of several lava domes on ___ ______________ _________.
Soufriere Hills Volcano have rendered more than half of the Caribbean island of Montserrat uninhabitable
Large mantle plumes, dubbed __________________, are thought to be responsible for the vast outpourings of basaltic lava that created the large basalt provinces.
Superplumes
The mechanisms that generate these mantle-derived magmas are essentially the same as those that create volcanic island arcs.
The most significant difference is that continental crust is much thicker and is composed of rocks having higher silica content than oceanic crust.
The collapse of lava domes, particularly those that form on the summit or along the steep flanks of composite cones, may produce powerful pyroclastic flows.
These flows result from highly viscous magma slowly entering the dome, causing it to expand and steepen its flanks.
As the slab sinks deeper into the mantle, the increase in temperature and pressure drives water and carbon dioxide from the oceanic crust.
These mobile fluids migrate upward and reduce the melting point of hot mantle rock sufficiently to trigger some melting.
These volcanic chains develop roughly parallel to the associated ___________.
Trench at distances 200 to 300 km (100 to 200 miles)
The capital city, Plymouth, was destroyed and ___________ of the population that evacuated.
Two-thirds
A few years earlier, a collapsed lave dome at the summit of Japan's Mount _____ produced a ________________________ __________ that claimed 42 lives
Unzen Pyroclastic flow Many of the victims were journalists and filmmakers who ventured too close to the volcano in order to obtain photographs and document the event.
Crater Lake, Oregon
image
Section 5.2 The Nature of Volcanic Eruptions
Volcanic activity is commonly perceived as a process that produces a picturesque, cone-shaped structures that periodically erupts in a violent manner Many eruptions are not explosive
Volcanism at a convergent plate margin results in the development of a slightly curved chain of volcanoes called a ____________ ________.
Volcanic arc.
Geologists prefer the more descriptive term ________________ _______ _____or simply _______ _____
Volcanic island arcs Or island arcs
This causes the burst the burst of __________ that emits voluminous outpourings of lave to form a huge basalt province in a matter of million or so years.
Volcanism
Prior to the development of the theory of plate tectonics, geologists did not have an acceptable explanation for the distribution of Earth's___
Volcanoes
Kilauea caldera
image
The injection of a fresh supply of hot molten rock heats and remobilizes the semi-fluid magma ________________.
chamber
Lesser amounts of ______
chlorine, hydrogen and argon
These eruptions tend to steepen the slope of summit area, which often becomes capped with clusters of _____________ ______________.
cinder cones
Some of these eruptions may have an impact on Earth's ________________.
climate
Pyroclastic flows are generated by the ___________________ of tall eruption columns during an _________________________ event.
collapse explosive
A conical shape with a steep summit area and gradually sloping flanks is typical of most large __________________________ cones.
composite
Hawaii's Kilauea Volcano
generated relatively quiet outpourings of fluid lavas gentle eruptions are not without some fiery displays. fountains of incandescent lava sprays hundreds of meters in the air most recent active phase began in 1983 180 homes destroyed national park visitor center destroyed
Some volcanic structures that appear to be somewhat randomly distributed around the __.
globe
Pyroclastic flows are propelled by the force of _______________________- and tend to move in a manner similar to snow avalanches
gravity
These fountains are usually __________ and not associated with major explosive events that cause great loss of life and property.
harmless
aa
have surfaces of rough, jagged blocks with dangerously sharp edges and spiny projections aa lavas cannot change to pahoehoe
In some settings, _____________ temperature basaltic magmas reach Earth's surface, where they produce highly _____________ lavas.
high fluid
3. Yellowstone - Type Calderas
historic and destructive eruptions such as Mount St. Helens and Vesuvius pale in comparison what happened 630,000 years ago in the region now occupied by Yellowstone National Park 240 cubic miles of pyroclastic material erupted. catastrophic eruption sent showers of ash as far as the Gulf of Mexico and resulted in the formation of a caldera (43 miles across) vestiges of this event are the many hot springs and geysers in the Yellowstone region
In 1991, a hot ash cloud from Japan's Unzen Volcano engulfed and burned hundreds of ______________ and moved cars ___________________________ feet.
homes 250 feet
over the next 3 years, the general eruptive patterns consisted of short periods __________ to ______________ when fountains of gas-rich lava sprayed skyward.
hours to days
These large volume eruptions account for the majority of _________________ _________________
human fatalities
With the exception of the volcanic islands that form above subduction zones, most other small oceanic islands are either a single _________________ volcano or the coalescence of two or more shields built on massive amounts of pillow lavas
shield
In contrast to fluid basaltic magmas that can travel many kilometers, viscous andesitic and rhyolitic magmas tend to generate relatively ______________ prominent flows.
short.
A magma's viscosity is directly related to its _________________ content.
silica
The _______________ rich magmas typical of composite cones generate thick, viscous lavas that travel less than a few kilometers.
silica
The more ______________ in magma, the greater is viscosity. Silica impedes the flow of magma because silicate structures start to link together into long chains early in the crystallization process.
silica
Composiste cones reflect the viscous nature of the material from which they are made. In general, composite cones are the product of _____________ - ___________ magna having an __________________________composition.
silica -rich andesitic
Most cinder cones are produced by a ___________, short-lived eruptive event.
single
Shiprock is higher than most _______________________ and one of many such landforms that protrude conspicuously from the red desert landscapes of the _______ ________.
skyscrapers American SouthWest
Cinder cones have simple, distinct shapes determined by the ________ that loose pyroclastic material maintains as it comes to rest.
slope
On the Big Island of Hawaii, these lavas have been clocked at 19 miles per hour down steep ______________. Flow rates of 30 to 1000 feet per hour are more common.
slopes
The movement of silica - rich rhyolitic lava may be too _______________ to perceive.
slow
For up to 24 hours before an eruption, swarms of ___________________________ warn of the impending activity
small earthquakes
pahoehoe
smooth surfaces that sometimes resemble twisted braids hotter and more fluid pahoehoe can change into aa lavas
Most magma originates in rocks from Earth's upper mantle that is essentially
solid, not molten
In the final stage of growth, shield volcanoes erupt more ____________________________, and __________________________ ejections are more common.
sporadically pyroclastic
Cinder cones have high angle of repose (the steepest angle at which material remains stable are are therefore ______-sided, with slopes between 30 and 40 degrees.
steep
This may explain why Mauna Kea, which is more mature volcano that has not erupted in historic times, has a _________________ summit than Mauna Loa, which erupted in 1984.
steeper
Felsic (rhyolitic) lavas are very viscous and tend to form short, _______________ flows.
thick
One hazard associated with volcanoes is their ability to produce ________________
tsunamis
conduit in volcano
tube where magma comes up through
In addition, most of the lava (80%) flowed through a well-developed system of lava _____
tubes
Occasionally, the lake overflowed, but more often lava escaped through ____________ to feed flows that moved down the southeastern flank of the volcano toward the sea.
tunnels
pillow lavas
useful in reconstruction of geologic history because their presence indicates that the lava flows formed below the surface of a water body
By the summer of 1986, a new _______ opened 2 miles downrift.
vent
During the night, hot, glowing rock fragments were ejected from the __________, producing a spectacular fireworks display.
vent
Once the event ceases, the magma in the plumbing connecting the _______ to the magma source solidifies, and volcano usually does not erupt again.
vent
Most of the volume of a cinder cone consists of pea to walnut sized fragments that are markedly __________________ and have a black to ________________________ color
vesicular reddish-brown
Lavas increase in ____________________, resulting in thicker, shorter flows
viscosity
In contrast to hot basaltic lavas, cool silica -rich rhyolitic lavas are so __________ that they hardly flow at all.
viscous
magmas contain varying amounts of dissolved gases called __________________
volatiles, held in the molten rock by confining pressure, just as carbon dioxide is held in cans and bottles of soft drinks
Cinder cones number in the thousands around the globe. Some occur in groups such as the ____________________ field near _________________, Arizona
volcanic field Flagstaff, Arizona