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