MaarsAlso, called,"tuff cones," maars

are shallow, fiat-floored cratersthat scientists interpret haveformed above dlatremei a a resof 'a violet)) expansion of ag tic

.gas or stee.ni, deep erosi f amaar, presumably would expose adiatreme. Maars range in,sizefrom 200 to 6,500 feet across andfrom 30 to 650 feet deep, and mostare commonly filled with water_ to.form natural lakes. Most mawshave low rims composed of amixture of loose fragments ofvolcanic. rocks and rocks torn -from the wails of the diatreme.-

Iv ars occur in the westernIf ited States, in the Eifel region of

ermany, and in other_geologicallyyoung volcanic regioneof theworld. An excellent example of amass; Is Zuni Silt Lake in NewMexico, a shallow saline lake thatoccupies a flat-flowed craterabout 6,500 feet across and 400feet deep. itslow rim,is composedof tabu) pieces of basaltic _lavaand wallrocks (sandstone, shale,limestone) of the underlying dbktreme. as well as.random chunksof ancient cryst..`line rocks blastedupward from griat depths.

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U.Sj Department cif the IntetiorkGeotegiCal Smiley

ti b. otrAPUIREttl OP illUGAIrniNATIONAL INSTITUTE OF EDUCATION

EDIJC-ArrOSiA4. RESOURGES INFORMATIONCENTER 'CRCs

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VOLCANOES

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"PERMISSION TO REPRODUCE ThiS .

MATERIAL/1AS BEEN GRANTED BY

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TO THE EDUCATIONAL RESOURCES.INFORMATION CENTER {ERICL

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The eruption of Cerro Negro Volcano, near Leda, Nicarague,OuringNoverribor 1968.

Volcanoesby Robe 1. Tilling

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Covet and Title Page. Lava fountains and flows. Mauna Loa. Hawau, July 6. 1976.

1 1

Volcanoes destroy and volcanolA create. The catastrophic eruptionof Mount St. Helens on May 18, 1980, made clear the awesome destructivepower of a volcano. Yet, over a time span longer than human memoryAnd record, volcanoes have played a key role in forming and modifyingthe planet upon which we live. More than 80 percent of the Earth'ssurfaceabove and below sea levelis of volcanic origin. Gaseousemissions from volcanic-vents over hundreds of Illations of years formedthe Earth's earliest oceans and atmosphere, which supplied theingredients vital to evolve and sustain life. Over geologic eons, countlessvolcanic eruptions have produced mountains, plateaus, and plains,which subSequent erosion and weathering have sculpted into majesticlandscapes and formed fertile soils.

Ironically, these volcanic soils and inviting butanes have attracted,and continuet attract, people to live on the flanks of volcanoes. Thus,as population ansity increases in regioni of active or potentially activevolcanoes, mankind must become increasingly aware of the hazardsand learn mot to "crowd" the volcanoes. People living in the shadow,ofvolcanoes must live in harmony with them and expect, and shot4d planfor, periodic violent unleashings of their pent-up energy.

This booklet presents a generalized summary of the -nature, work-ings, products, and hazards of the common types of volcanoes aroundthe world, along with a brief introduction to tile-tectiliques of volcanomonitoring and research.

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Op August 24, A.D. 79,Vesuvius Volcano suddenly ex-ploded and destroyed the Romancities of Pompeii arid Herculbneum.Although Vesuvius had shownstirringi of he when a succession

.. of earthquakes in A.D. 63 causedsome dainage, it had been literallyquiet for hundreds of years andwas considered "extinct." Itssarface and crater were__greenand- covered with vegetation, sothe eruption was totallyunexpected. Yet in a few hours,hot volcanic ash and dust burledthe two cities so thoroughly thatthpir ruins were not uncoveredfor nearly .1,700 years, when thediscovery of an outer wall in 1748started a period of modernarcheology. Vesuvius has con-tinued its activity intermittentlyever since A.D. 79 with numerousminor eruptions and severalmajor eruptions occurring in1631, 1794,1872, 1906 and in 1944

. in the midst of the Italian campaignof World War II.

In the United States On March27, 1980, Mount St. Helens Volcanoin the Cascade Range, south-western Washington, reawakenedafter more than a century ofdormancy and provided a dramaticand tragic reminder that thereare active volcanoes in the'lower 48" States as well as ir.

Hawaii and Alaska. The catastropheis motion of Mount St. Helenson May 18, 1980, and relatedmudflows and flooding causedsignificant loss of life (62 deador missing) and property damage(over $1.2 billion). Mount St.Helens Is expected to remain

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intermittently active for monthsor years, possibly even decades.

The word "volcano" comesfrom the little Island of Vulcanoin the Mediterranean Sea offSicily. Centuries ago, the peopleliving in this area believed thatVulcano was the chimney of theforge of Vulcanthe blacksmithof the Roman gods. Tkey thoughtthat the hot lava fragments andclouds of dust erupting fromVulcano came from Vulcan's forgeas he beet out thunderbolts forJupiter, king of the gods, andweapons for Mars, the god of war.In Polynesia the people attributederuptive activity to the beautiful butwrathful Pele, Goddess of Vol-canoes, whenever she was angryor spiteful. Today we know thatvolcanic eruptions 'ire nor super-natural but can be studied andinterpreted by scientists.

3

e

The Nature of Volcanoes

Volcanoes are mountains, butthey are very different from othermountains; -they- are not formedby folding and crumpling or byuplift and erosion. Instead,volcanoes are built. by the accumu-lation of their own eruptiveprodUctslava, bombs (crustedover lava blobs),ashflows, andtephra, (airborne ash and dust).A volcano is most commonly aconical hill or mountain builtaround a vent that connects withreservoirs of miten rock belowthe surface of the Earth, The termvolcano also refers to the opening

or vent through which the moltenrock and associates gases areexpelled.

Driven by buoyancy and gaspressure the mol'sn rock, whichis lighter than the surroundingsolid rock, forces its way upwardand may ultimately break throughzones of weaknesses In theEarth's crust. if so, an eruptionbegins, and the molten rodk maypour from the vent as nonexplosivelava flow's, or it may shootviolently into the air as denseclouds of lava fragment;. Largerfragments fall back around the

. ..

Fountalning lava and volcanic debris during the 1959 Kilauea lki eruption ofKilauea Volcano, Hawaii.

47

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vent, and accumulations of fall-back fragments may movedownslope as ash flows underthe Wive of gravity. Some of thefiner ejected materials may becarried by the wind only to fallto the ground many allies away.The finest ash particles may beinjected miles into the atmosphereand carried many times aroundthe world by stratospheric windsbe;ore settling out,

Molten rock below the surfaceof the Earth that rises in volcanicvents is known as magma, butafter it erupts from a volcano itis called lava. Originating manyt..ns of miles beneath the ground.the ascending magma commonlycontains some crystals, fragmentsof surrounding (unmelted) rocks,and dissolved gases, but it isprimarily a liquid composed prin.L.ipally of oxygen, silicon,

aluminum, iron, magnesium,calcium, sodium, potassium,titanium. and manganese. Magmasalso contain many other .chemicalelements in trace quantitiO.Upon cooling, the liquid magmamay precipitate crystals of variousminerals until solidification iscomplete to form an igneous ormagmatic rock.

The accompanying diagram ofa volcano in an oceanic.environ-ment shows that heat concentratedin the `Earth's upper mantle raisestemperatures sufficiently to meltthe rock locally by fusing thematerials with the loweStmeitiagtemperatures, resulting intsmall,isolated blobs of magma. Theseblobs thin collect, rise throughconduits,and fractures, and someultimately may recollect in largerpockets or reservoirs ("holdingtanks") a few miles beneath the

_eTsmimI411°14111111._

An Idealized diagia of a_voicand 4n an oceanic environment {felt) and on a continentalernoireninent (right). g

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Earth's surfa9e. Moun ting presiurewithin the. retervoir may drive themagma further upward throughstructurally weak zones to erupt aslava at the surface. irlticontinentalenvironment magmas are gener-ated in the Earth's crust as wellas at varying depths in the uppermantle. Ilia variety of moltenrocks the crust, plui thepossibility of mixing with moltenmaterials from the underlyingmantle, leads to the production oftriagmas with widely differentchemical compositions,

If magmas cool rapidly, asmight be expected near or on theEarth's.surlace, they solidify toform igneous rocks that are finelycrystallirke or glassy with fewcryMals. Accordingly, lavas, whichof course are very rapidly cooled,form volcanic rocks typicallycharacterized by a small percent-age of crystals or fragments setin a matrix of glass (quenchedor super-cooled magma) or finergrained crystalline materials,If magmas never breach thesurface to erupt and remain deepunderground, they cool muchmore slowly and thus allow ampletime to sustain crystal precipita-tion and growth, resulting in theformation of coarser grained,nearly completely crystalline,igneous rocks. Subsequent to finalcrystallization and solidification,such rocks can be exhumed byerosion many thousands or millionsof years later and be exposed aslarge bodies of so-called graniticfocks, as. for example, thosespectacularly displayed in-Y6samite National 'Park and

8.

other parts of the majestic SierraNevada mountains of California.

Lava is red-hot when It poursor blasts out of a vent but soonchanges to dark red, gray, black,or some other color as it coolsand _solidifies. Very hot, gas -richlava containing abundant iron and .

magnesium is fluid and flows likehot tar, whereas coolerivas-poorlava high in silicon, sodium, andpotassium flows sluggishly, likethick honey in some cases orin others like pasty, blockymasses.

zre__

Two Polynesian terms are used to Identifyme sumacs character of Hawaiian lavaflows. As, a basalt with &tough. blockyappearance, much like furnace slag, isshown at the top. Pahoerme. a mote fluidvariety with a mooth,-satiny and some-limes glassy appearance. is shown at thebottom

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,All magmas contain dissolved

gases, and as they rise to thesurface to erupt,'the Onfining'pressures are reduced 'and thedissolved gases are liberatedeither quietly or explosively.If the lava ;s a thin, fluid (not .

viscous), the gases may escape_-hilasilkBut if the lava is thick and

pasty (highly viscous), the gaseswill not move-freely but will buildup tremendous pressure, andultimately escape with 'explosiveviolence: Gases in lava may bk. ,compared with the gas in a bottleof a catbOnated soft drink. if yog..put your thtimb over the top of thebottle and shake it vigorously, thegas separates' from the drink andforms bubbles. When you remove

your thumb abruptly, there isa miniature explosion of gas andliquid. The gases in lava behavein somewhat the same way...Their sudden expansion causesthe terrible explosiorg that throwout great masses of solid rockas well as lava, dust, and ashes.

The violent separation of gasfrom lava may produce rock frothcalled_pumice. Some of this frothis so lightbecause of the manygas bubbles --that it floats onwater. In many eruptions, thefroth is shattered explosively intosmall fragments that are hulledhigh into the air in fhe form ofvolcanic .cinders (red or black),volcanic ash (commonly tan orgray), and volcanic dust.

.

During the 1959eruption of Kilaueatkl, tounlaininglava and volcanicdebris completelyblocked severalor the roads in jbaHawaii Volcanoes

1

/National Park, /

/ 7

Principal Types of Volcanoes

Geologist, gene/

rally group't vol-canoes)nto. four main lunar-cinder cones, composite volcanoes.shield- volcanoes, and lavaddmes.

Cinder conesCinder cones are the siMpleit

type of volcano. They are built.from .particles and blobs ofcongealed lava ejected fromsingle vent. As the gas-chargedlava is blown violently into theair, it breaks into small fragmentsthat solidify and fall as cinders

around the vent to form a qiccularor oval cone. Most cinder coneshave a bowl-shaped crater atthe summit and rarely rise morethane, thousand feetor so alaci9etheir surroundings. Cinder conesare numerous in western NorthAmerica as well as throughoutother volcanic tetrains of the .

world.In:1943 a cinder cone started

growing on a farm neer.the villageof Paricutin in Mexico. Explosiveeruptionkcaused by gas rapidlyexpanding and escaping from

Es.

Schematic rapipsentatiort of the. internal structure sit a .tygneal.cinny- cone.,

0

molten lava formed cinders thatfell back around the vent, building'up the cone to a height of11200 feet. The last explosiveeruption left a funnel-shapeddepression called a crater at thetop of the cone. After the excessgases had ,largely dissipated, themolte'n roc,k quietly poured outon the surrounding surface ofthe cone and Moved downslopeas lava flows. This cird,er_ofevents -- eruption, formationcane and crater, lava flowis

:l

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a common sequence in theformation of cinder cones.

During 9 years of activityParicutin built a prominent cone,coveretraboat 100 s4uare Man-with ashes, and destroyed thetown of San ,Juan. Geologistsfrom many parts of the worldstudied Paricutin during its lifetimeand learned a great deal aboutvolcanism, its products, and.,the.modification of a volcanic land-form by erosion.

a

Parfoutiri yolcaoo, exlcp, M a .cinder cone rising approximately 1,200 Met abovethe surrounding pi 11.

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Composites volcanoes...

Some 0 the Earth's grandestmountains are compositevolcanoessometimes calledstratovolcanoes.,They aretypically steep - sided, symmetricalcones of large dimension builtof alteinating layers of lava flows.volcanic ash, cinders, blOcks,and ,bombs and may rise asmuch as 8,000 feet above theirbases, Some of the most conspicu-ous and beautiful mountains inthe world are composite volcanoes,including Mount Fuji in Japan,Mount Cotopaxi in Ecuador,

Mount Shasta in California,Mount Hood in Oregon, andMount St. Helens and Mount

--Rainier in Washington.Most composite volcanoes have

a crater at the summit whichcontains a central vent or aclustered group of vents. Lavaseither flow through breaks inthe crater wall or issue fromfissures on the flanks of thecone. Lava, solidified within thefissures, forms dikes that act asribs which ,greatly strengthenthe cone.

The essential feature of acomposite volcano is a conduit

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Schematic representalion at the mettle( etre-tore or a Apkcal composite volcano_10 .. -----10

system through which magmafrom a reservoir deep in theEarth's crust rises to the surface.The volcano is built up by theaccumulation of materialerupted through the conduit andincreases in size as lava,cinders, ash, etc., are addedto its slopes.

When a composite yolcanobecomes dormant, grown beginsto destroy As the coneis stripped a ay, the hardenedmagma filljng the conduit (thevolcanic 'Plug) and fissures

As.

(the dikes) becomes exposed,and it too is slowly reduced byerosion. Finally, all that remainsis the plug and dike complexprojecting above the land surfacea telltale remnant of the vaneished volcano.

An interesting variation of acomposite volcano can be seep....,at Crater Lake in Oregon. Fromwhat geologists can interpret ofits past, a high volcanocalledMount Mazamaprobablysimilar in appearance to present-day Mount Rainier was once

Shisbaidin volcano an imposing composite cone. towers 9.372 feet above sea level

in the Aleutian Islands. Alaska.

14

or- .-r. I. .,,y.

__----Crater LaicCOregon. Wizard Island. _a Cinder cone. rises above the lake surface.

located at this spot. Followinga series of tremendous explosionsabout 6,600 years ago, the volcanolost its top. Enormous volumesof voicanIQ ash and dust wereexpelled and swept down theslopes as ash flows and ava-lanches. These large-volumeexplosions rapidly drained thelava benSath the mountain andweakened the upper part. Thetop then collapsed to form a largedepression, which later filled withwater and is now completely oc-cupied by beautiful Crater Lake.A last gasp of eruptionsproduced a small cinder conewhich rises above the water

surfac? 3 Wizard Island in, andnear tilt> rim, of the lake.Depressions such as Crater Lake,formed by collapse of volcanoes,are known as calderas. They areusually .{arge, steep-walled,basin - shaped depressions formedby the collapse of a large areaover, and around, a volcanicvent or vents. Calderas rangein form and size from roughlycircular depressions 1 to 15miles in diameter to hugeelongated depressions as muchas 60 miles long.

The Evolutionof a Composite Volcano:

a. Magma, rising upwardthrough a conduit, erupts atthe Earth's surface to form avolcanic con. Lava flowsspread overihe surroundingarea.

C.

b. As volcanic activity con-tinues, perhaps over spans ofhundreds of years, the cone isbuilt to a great height and lavaflows form an extensivo plateauaround its base. During thisperiod, streams enlarge anddeepen their valleys.

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c. When volcanic activitycanes, erosion starts todestroy the cone. After thou-

- of years, the great conestrppeii away to expose the

hardened "volcanic 1..ug" inthe conduit. During this period2eg,Lr.

d. Continued erosion removesall traces of the cone and theland is worn down to a surfaceof low relief. All that remainsis a protecting plug orvolcanic neck," a small lava-

capped mesa, and vestiges of .heonce lofty volcano and its star-rounding lava plateau.

of inactivity, streams broadentheir valleys and dissect litelava plateau to font, Isolatedlava-capped mesas. 0

-- 1613

Shield volcanoes

Shield volcanoes, the third typeof volcano, are built almost en-tirely of fluid lava flows. Flow afterflow pours out in all directionsfrom a central summit vent, orgroup of vents, building a broad,gently sloping cone of fiat. domicalshape. with -a profile much likethat of a warrior's shield. They arebuilt up slowly by the accretion ofthousands of flows of highly fluidbasaltic (from basalt, a hard, densedark voNanic rock) lava thatspread widely over great distances,and then cool as thin, gently dip-ping sheets. Lavas also commonlyerupt from vents along fractures(rift zones) that develop on theflanks of the cone. Some of thelargest volcanoes in th (odd areshield votsanoos. In northern Cali-fornia and Oregon, many shieldvolcanoes have diameters of 3 or 4miles and heights of 1.500 to 2.000feet. The Hawaiian islands arecomposed of linear chains of thesevolcanoes including Kilauea andMauna Loa on the island of Hawaiitwo of the world's most activevolcanoes. The floor of the oceanis more than 1,.000 feet deep atthe bases of the islands. As MaunaLoa. the largest of the shield volca-noes {and also the world s largestactive volcano). piojects 13,677feet aDOve sea level, its top is over28.000 feet above the deep oceanfloor.

In some shield-volcano erup-tions. basaltic lava pours outquietly from long fissures instead ofcentral vents and Hoods the sur.rounding countryside with lava

14 :*

..^'"ZIMtt°11111113"111"......t,_

Mauna Loa Volcano. Hawaii. a.giant amongthe active volcanoes of the. world. Snow.capped Mauna Kea Volcano in the distance

flow upon lava flow, forming broadplateau:. Lava plateaus of this typecan be seen,:n Iceland. southeast-ern Washington. eastern Oregon.and southern Idaho. Along theSnake River in Idaho. and theColumbia River in Washington andOregon. these lava flows arebeautifully exposed and measuremore than a mile in total thickness.

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Internal structure of a lypfcal shield volcano-

16

Lava Domes

Volcanic or lava domes areformed by relatively small bulbousmasses of laya too viscous to flow'any great consequently,on extrusion, he lava piles overand around its vent. A dome growslargely by exp nsion from within,As it grows its uter surface coolsand hardens, then shatters, spillingloose fragment down its sides,

_

Some domes form craggy knobs orspines over the volcanic vent,whereas others form short, steep-sided lava flows known as

coulees." Volcanic domes co's-11-mo* occur within the craters oron the flanks of large compositevolcanoes. The nearly circularNovarupta came that formedduring the 1912 eruption of KatmaiVolcano, Alaska,: measures 800feet across and 200 feet high. Theinternal structure of this dome-

- grow_ 4I 4

415:610P11101"Iredr ._ joi,

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defined by layering 'of lava fanningupward and outward from thecenterindicates that it grewlargely by expansion from within,Mount Pelee in Martinique, WestIndies, and Lassen Peak and Mono

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A sketch of the havoc wrought in 51 Pierre Harbor on Martinique during the eruptionof Mount Pelee in 1902-

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The Novarupta Dome famed during the 1912 eruption of Katmai Volcano. Alaska

domes in California are exampleiof lava domes. An extremely de-structive eruption accompaniedthe growth of a dome at MountPelee in,1902. The poastal town ofSt. Pierre,-about 4 miles downsjopeto the south,was demolished andnearly 30,000 inhabitants were

killed by an incandescent, high-yelocity ash flow and associatedhot gases and volcanic dust. Onlytwo men sui :ved; one because he

was in a poorly ventilated,dungeon-like jail cell and the otherwho somehow made his way safelythrough the burning city,

Schematic reprasentaftn of the Internal Onrcture of a typical volcanic do 0.

-/ it

Other Volcanic StructuresPlugs (necks)

Congealed magma, along withfragmental volcanic and walirockmaterials, can be preserved in thefeeding conduits of a volcano uponcessation .)f activity. These pre-served rocks form crudely cylin-drical masses, from which projectradiating dikes; they may bevisualized as the fossil remains ofthe marls of a 4oicano !theso-caued volcanic plumb4rig sys-tem ) and are referred to asvolcanic plugs or necks. Theigneous material in a plug mayhave a range of composition

- similar to that of associated lavasor ash, but may also include frag-ments and blocks of denser,coarser grained rockshigher iniron and magnesium, lower insiliconthought Co be samples ofthe Earth's deep crustror upperFyi_antie plucked and transportedby the ascending magma. 'Manyplugs and-'necks are largely nrwholly composed of fragmentalvolcanic material and of fragmentsof walirock, which can be of anytype. Plugs that bear a particularly

, strong imprint of explosive erup-bon of highly gas-charged magmaare called diatremes or tuff-breccix-,.Volcanic plugs are believed to

oVerlie a body of magma whichcould be either still largely liquidor completely-solid depending onthe state of activity of the volcano,Plugs are known, or postulated, tobe commonly funnel phaped and totaper downward into bodies in-

creasingly elliptical in plan orelongated to dike-like forms.Typically, volcanic plugs and necks

tendto be more resistant to ), 'erosionthan their enclosing nickformations, Thus, after the volcanobecomes inactive and deeplyeroded, the exhumed plug may

stand up in bold relief as anirregular, columnar structure. Oneof the best krioWn and most spec-tacular diatremes in the UnitedStates is Ship Rock in New MexiCo,which towers some 1,700 feetabove the more deeply erodedsurrounding plain. Volcanicplugs,

Including diatremes, are foundelsewhere in the western UnitedStates and also in Germany.South Africa. Tanzania. andSiberia.

Shirt Rock, San Juan County, New Mexico.

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46!

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MaarsAleo.called,"tuff cones," meats

are shallow, flat- floorea cratersthat scientiqs interpret haveformed abbve dlatremeia a resof a violet); expansion of agt is

.gas or steam, deep erosion amaar, presumably would expose adiatreme. Mears range in.sizefrom 200 to 6,500 feet across endfrom 30 to 650 feet deep, and mostare commonly filled with water. toform natural lakes. Most mawshave low rims composed of amixture of loose fragmants ofvolcanic rocks and rocks tornfrom the walls of the dlatreme.

lars occur In the westernited States, in the Eifel region of

ermany, and 19 other.geologicallyyoung volcanic regiOns of theworld. An excellent example of ameat is Zuni Silt Lake in NewMexico, a shallow saline lake thatoccliples a flatr.flocred_ craterabout 6,500 feet across and 400feet deep. Its-low anis composedof lobse pieces of basaltic lavaand wallrocks (sandstone, shalelimestone) of the underlying dia,treme. as well as. random chunkio( ancient cryst...'llne rocks blastedupward from great depths.

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Zuni Salt Lake Maar, Catron County. New Mexico.

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20

Cryptovoicanic structuresSome well-exposed, nearly

circular areas of intensely de- ,

forme,: sedimentary rocks, inwhich a central vent-14%e feature issurrounded, by a ring-shapeddepression, resemble volcanicstructures_in.gross form. As noclear evidence ol vo:canic origincould be found in or near thesestructures, scientists initiallydesCribed them as -cryptovol-canic," a term now not often used.Recent studies have shown that notall craters are of volcanic origin.Impact craters, formed by colli-sions with the Earth of large mete-orites, asteroids, or comets, sharewith volcanoes the imprints ofviolent origin, as eyidenced bysevere disruption, _and even localmelting, of rock. Fragments of me-,teorltes or chemically detectabletraces of extraterrestrial materialsand indications .of strong forcesacting from above, rather than frombelow, distinguish impact fromvolcanic features,

Scientists now generally con-sides% cryptovolcanic structures

_

to be nonvoicanic in origin, such ,-as: impact of extraterrestrialbodies; subsurface salt-domeintrusion (and subsequent dissolu -'

tion and collapse), collapse .ausedby subsurface limestone dissolu-tion and, or ground-water with-drawal; and collapse related tomelting of glacial ice. An impres-sive example of an impact structureis Meteor Crater, Ariz., which is ,

visited by thousands of touristseach year. This impact crater,4,000 feet in diameter and 600feet deep, was formed in the geo-logic past (probably 30,000-50,000years before present) by a meteor-ite striking the Earth at a speed ofmany thousands of miles per.hour.

In addition to Meteor Crater,very fresh, morphologically distinct,impact craters are found at threesites near Odessa, Tex., as wellas 10 or 12 other locations in theworld. Of the more deeply eroded.less obvious, postulated impactstructures, there are about ten well-established sites in the UnitedStates .and perhaps80 or 90 else-where in the world.

.

.004.4".

Meteor Crater. Arizona.

21

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Types of Volcanic Eruptions

During an episode of activity, avolcano commonly displays adistinctive pattern of behavior.Some mild eruptions merely die-.charge steam and other gases,whereas other eruptions quietlyextrude quantities of lava. Themost spectacular eruptions consistof violent explosions that blastgreat clouds of gas-laden debrisinto the atmosphere.

The type of volcanic aruption isoften labeled with the Ame of awell-known volcano where. char-acteristic behavior is similarhence the.use of such terms as"Strombollan," "Vulcanjan,""Vesuvian, "Pe lean," "Hawaiian,""Phreatic" and others. Some vol-

.. canoes may exhibit only one .har-acteiistic type of eruption du. ng aninterval of activityothers maydisplay an entire sequence oftypes.

in a Strornboliantype erup-tion observed during the 1965activity of Irazu Volcano in CottaRica, huge clots of molten lavaburst from the summit crater to .

form luminous arcs through thesky. Collecting on the flanks ofthe cone, laya clots combined tostream down .he slopes in fieryrivulets.

in contrast, the eruptive activityof Paricutin Volcano in 1.'247demonstrated a `Nulcanian"-typeeruption, in which a dense cloudof ash-laden gas explodes from thecrater and rises high above thepeak. Steaming ash forms awhitish cloud near the upper levelof the cane.

In a "Vesuvian" eruption, as.typified by the eruption of MountVesuvius in Italy in A.D. 79, greatquantities of ash-laden gas areviolently discharged to form a

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ke,jfer /f* wom...

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trazO Volcano, Costa Rica, 1965.

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Pariautin.VOicsnO,,Mexico, 1947

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it/ 1 It- NV. ill :0.;.f.-4 4 i4 -a P

14.--

aMount Vesuvius Vol-cano, Italy, 1944.

25

a

cauliflower-shaped cloud highabove the volcano.

In a "Pe lean" or "Nuee Ardeote"(glowing cloud) eruption, such asoccurred on the Mayon Volcano inthe Philippines in 1968, a largequantity of gas, dust, asilLand.incandescent livifrajments areblown out of a central crater, fallback, and form tongue-like, glow-ing avalanches that move down-slope at velocities as great as 100'Mlles per hour. Such eruptiveactivity can cause great destruc-tion and loss of life if it occurs inpopulated areas, as demonstratedby the devastation c 3t, Pierreduring the 1902 eruption ofPelee on Martinique. West Indies.

"Hawaiian" eruptions may occuralong fissures or fractures thatserve as linear_vents, such asduring the eruption of Mauna LoaVolcano in Hawaii in 1950, or theymay occur at a central vent suchas during the 1959 eruption in

'

Kilauea Iki Crater of Kilauea Vol.cano, Hawaii. In fissure-typeeruptions, molten, incandescentlava spurts from a fissure on thevolcano's nft zone and feeds lavastreams that flow downslope. Incentral-vent eruptions, a_ fountain .

of fiery lava spurts to a height ofseveral hundred feet or more.Such lava may collect in old pitcraters to form lava lakes, or fo mcones, or feed radiating flows.

The eruption of Taal Volcano inthe Philippine Islands in 1965typifies "Phreatic" (or steam-blast)behavior, Here, a great column ofsteam, dust, ash, and cinders isblasted to a height of severalthousand feet. This type of violenteruption is believed to occur whena large quantity of ground or sur-face water comes in contact withhot rock or magma in a volcanicvent and is instantly and explosive-ly flashed to steam.

Mauna Too Volcano, Hawaii. 'fag).

26

Submarine Volcanoes

Submarine volcanoes and vol-canic vents are common featureson certain zones of the ocean floor.Some are active at the presenttime and, in shallow water, disclosetheir presence by blasting steamand rock-debris high above thesurface of the sea. Many otherslie at such great depths that thetremendous weight of the waterabove them results in high, con-fining pressure and prevents theformation and explosive releaseof steam and gases. Even verylarge, deepwater eruptions maynot disturb the ocean surface.

The unlimited supply of water sur-rounding submarine volcanoes cancause them to behave differently fromvolcanoes on land. Violent, steam-blast eruptions take place whensea water pours into active shallowsubmarine vents. Lava, eruptingonto a shallow sea floor or flowinginto the sea from land, may coolso rapidly that It shatters into sandand rubble. The result is the pro-duction of huge amounts of frag-mental volcanic debris. The famous"black sand" beaches of Hawaiiwere created virtually Instantane-ously by the violent Interaction

1

WIN-nano representation Oa typical aubmarine eruPlion in the open ocean,

between hot lava and sea water.On the other hand, recent obser-vat: 's made from deep-divingsubmersibles have shown thatsome submarine eruptions produceflows and oth er volcanic structuresremarkably similar to thoseformed on land.

During an explosive submarineeruption in the shallow open ocean,enormous piles of debris are builtup around the active volcanic vent.Ocean currents rework the debris

IP

in shallow water, while other debrisslumps from the upper part ofthe cone and flows into deep wateralong the sea floor. Fine debrisand ash to the eruptive plume arescattered over a wide area inairborne clouds. Coarse debris inthe same eruptive plume rains intothe sea and settles on the flanksof the cone, Pumice from theeruption floats on the water anddrifts with the ocean currentsover a large area.

t7iztt-,- -fr-..re =_ _

7

---sPm

Submanne etupbon of Mybon-abo %Pocono. Izu islands, Japan on September 23. 1952

a

Geysers, Fumaroles, and

Geyse6, furnaroles (also calledsollataras), and hot springs aregenerally found in regions o: youngvolcanic activity. Surface waterpercolates downward through therocks below the Earth's surface tohigh-temperature regions sur-rounding a magma resell/cif, eitheractive or recently solidified butstill hot, There the water is heated,becomes less dense, and risesback to the surface along fissuresand cracks. Sometimes thesefeatures are called "dying vol-f-anoes" because they seem torepresent the last stage of volcanicactivity as the magma, in depth,cools and hardens.

Hot Springs

Erupting geysers provide spectacvlar displays of undergroundenergy suddenly unleashed, buttheir mechanisms are not com-pletely understoud. Large amountsof hot water are presumed to fillunderground cavities. The water,upon further heating, is violentlyejected when a portion of it sud-denly flashes into steam. Thiscycle can be repeated with re-markable regularity, as forexample, at Old Faithful Geyser inYellowstone National Park, whichhas erupted an an average ofabout once every 65 minutes.

Fumaroles, which emit mixturesof steam and other gases, are fed

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by conduits that pass through thewater table before reaching thesurface of the ground. Hydrogensulfide (H2S), one of ttie\typicalgases issuing from fumares,readily oxidizes to sulphuric acidand native sulfur. This accountsfor the intense chemical activityand brightly colored rocks in manythermal_areas.

Hot springs occur in manythermal areas where the surface

of the Earth intersects the patertable. The temperature and rate ofdischarge of hot springs dependon (actors such as the rate atwhich water circulates through thesystem of underground channei-ways. the amount of heat suppliedat depth, and the extent of dilutionof tne heated water by cool groundwater near the surface.

Black Growler steamvents tlumaroles).Norris Basin. Yellowstone National Park.Wyoming.

. .

Mammoth tiot Springs. Yellowstone National-Park. Wyoming

34

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31

Volcano Environments

There are more than 500 activevolcanoes kthose that have eruptedat east once within recorded his-tory) in the world-50 of which arein the United States (Hawaii,

32

Alaska, Washington, Oregon. andCalifornia)although many mordmay be hidden under the seas.Most active volcanoes are strunglike beads along, or near, the

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margins of the continents, andmore than half encircle the PacificOcean as a "Ring of Fire."

Many-volcanoes are in andaround the Mediterranean Sea.Mount Etna in Sicily is the largestand highest of these Mountains..

Italy's Vesuvius is the only activevolcano on the European mainland.Near the island of Vulcan°, thevolcano Stromboli has been in a

The distribution of some of:the Earth'svolcanoes.

60°

Mt. Katmai

Mt- Kiln%Slashelairt_ Mt. St. Helens

Mt. Sheitif40°

40°

state of nearly continuous, milderuption since early Roman times.At night, sailors in ithe Mediterra-nean- -can see.the glow from thefiery. molten_ material that is hurledinto the air. Very appropriately,Stromboilhas been called "thelighthouse of the Mediterranean."

--Some volcanoes crown islandareaslying 'near the continents,

-and Oth.ers_form chains of Islandsin the.deep ocean basins. Vol-canoes tend to cluster -tongnarrow mountainous belts wherefolding -and fracturing of the rocksprovide channeiways to !he surface..for the escape of megrim. Sig-nificantly, major earthquakes alsooccur along these belts, indicatingthat volcanism and seismic activityare often closely related, respond-irig to the 'same dynamic Earthforces,

in a- typical "Island-ere envi7ronment, volcanoes lie along thecrest of an arcuate, crustal ridgebounded on its convex side by adeep oceanic trench. The granite.or granitelike layer of the continen-tal crust .extends beneath theridge to the vicinity of the trench.Basaltic magmas, generated inthe mantle beneath the ridge, risealong fractures through the graniticlayer, These magmas commonlywill be moclifieck,or changed incomposition during passagethrough the granitic layer anderupt on the surface to form vol-canoes built largely of nonbasalticrocks.

In a typical "oceanic" environ-ment, volcanoes are alined alongthe crest of a broad ridge thatmarks an active fracture system in

the oceanic crust. Basaltic mag-mas, generated in the uppirmantle beneath the ridge, risealong fractures through the basaltic_layer. Because the granitic crustallayer is absent, the magmas arenot appreciably modified orchanged in composition and they

. _

Mount Sinabung, Sumatra_ ply_ J. .13gykr

Roberts (C) Notterta6GepgriphiA_Sege.kk

IslancberO environment...

erupt on the surface to formbasaltic volcanoes.

In the typical "continental"environment, volcanoes are to-gated in unstable, mountainousbelts that have thick roots cifgranite._or.granitelike rock. Mag-mks, generated near the base of

----1174--e;w'

the mountain root, rise slowly orintermittently along fractures Inthe crust During passage throughthe granitic layer, magmas arecommonly modified or changed Incomposition and erupt on The sur-face to form volcanoes constructedof nonbasaltiP mdse.-

--- - -

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aunkf-Kealletegiuktlew oulitAdams,-WaBhington.

57

Plate-Tectonics TheoryAccording to the new, gefierally

accepted "plate-tectonics" theoq,scientists believtthat the Earth's

' surface is broken into a number ofshifting _slabs_ or plates, whichaverage about_ 50 miles in.thick-

-ness. These Plates move relativeto one another above a hotter,Ileeper,_ more mobile zone at

----aver4g-e-tWei as great as a few__inehes per Year. Most of the world'sactivé viiicanoes are located alongor near the boundaries betweenshifting plates and are called.

e"plate-boundary" volcanoes. Flow-ever, some active volcanoes are

not associated with plateboundaries, and many of theseso-called "intra-plate" volcanoesform roughly Linear chains in the .

interior of somefoceagio_plates.Thd flawaijan Islands provide per-haps the,best example of an "Intra.plate,voicanio chain, develppedby the northwest-movirig,PacifloPlate -passing over, an inferred _

"hot spot" that initiates the _

magma-generation a_n_d -volcano- -

formation process. The peripheralareas of the Pacific Ocera_p-Basin,coritaining_the, boundaries-of. $ev-era) plates, are dotted by many

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. active volcanoes that form the so-called "Ring of Fire," The "Ring"providee excellent examples of _

"plate-boundary" volcanoes, in-cluding Mount St, Helens.

The accompanying. figure showsthe boundaries of lithosphere

..plateathat,ere presently active..,,The double lines indicate zones of"spreading from Whl-ah plates are-_moving- part. The tines with barbs

ioniCof_AinderthruSting(subduction), .where one plate_ is

Lithosphere plates of the Eart .

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sliding beneath another. The barbson the lines indicate the overridingplate, The Single line defines astrike-slip fault along which platesare sliding horizontally past oneanother. The stippled areas indicatea part of a continent, exclusive ofthat along .a. piste .bouncjaty,.whichis undergoing active ex_tensional,.compressional, or strike-slip

_ faulting.

In the Pacific Northyrest. the Juan deFuca Plate plunges beneath the NorthAmerican Plate, locally melting at depth:the'rnagma rises to feed and form theCascade volcanoes.

Extraterrestrial VolcanismVolcanoes and volcanism are

not restricted to the planet Earth.-Manned and unmanned. planetary.explorations, beginning in the late1960's, have furnished graphic

evidence of past volcanism and i

-.

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products on the Moon, Mars. Venusand other planetary bodies. Many

pounds of volcanic rocks werecollected by astronauts during thevarious Apollo lunar landing misr4sions. Only a small fraction of

112

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Manner 9 imagery of Olympus Mons Volcano on Mars compared to the eightprincipal Hawaiian Islands at the same scale (Mariner 9 image Mosaic, NASA/JPL).

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these samples have been sub-jected to exhaustive study byscientists, The bulk of the materialIs stored under controlled-environment conditions at NASA'sLunar Receiving Laboratory inHouston, Tex., for future study byscientists.

From the 1976-1979 Vikingmission. scientists have been ableto study the volcanoes on Marsarid their studies are very reveal-ing when compared with those ofvolcanoes on Earth. For example.Martian and *Ha-waiirn volcanoesclosely resemble each other inform. Both are shield volcanoes.have gently sloping 41aha, largemultiple collapse pits at theircenters,._and appear to be .built

ft

of fluid lavas that have left numer-ous floOt features on their flanksThe most obvious difference be-tween the two is size. The Martianshields are enormous. They cangrow to over 17 miles in heightand more than 350 miles across, incontrast to a maximum height ofabout 6 miles and width of 74miles for the Hawaiian shields,)

Voyager-2 spacecraft imagetaken of lo, a moon of Jupiter,captured volcanoes in the actualprocess of eruption, The volcanicplumes shown on the image risesome 60 to lOo milesabove thesurface of the moon. Thus, activevolcanisrii is taking place, atpresent, on at mast one planetary,body in addition to our Earth,

_; - 1 -

-

41-

Spacecraft ichige, made ".n-Jull 1979. shows volcanic plume rising Some 90 to 100miles above the surface of lo a moon of Jupiter (loyoger 2 phOlo. NASA).

Volcano Monitoring and Research

It has been said that the scienceof "volcanology" originated withthe accurate descriptions of theeruption of Vestiviusin A.D. 79contained in two letters from Plinythe Younger to the Roman his-torian Tacitus. Pliny's letters alsodescribed the death of his uncle,Pliny the Elder, who was killed inthe eruption. Actually. however, itwas not until the 19th century thatserious scientific inquiry into vol-canic phenomena flourished aspart of the general revolution inthe physical and life sciences, in-cluding the new science of "geol-ogy." In 1847, an observatory was.established on the flanks ofVesuvius r upslbpe from the site of_Hercula4eum, for the/Pore or lesscontinuous recording of the activityof the volcano that destroyed the

the city in A.D. 79. Still, throughthe first decade of the 20th cen-tury, the study of volcanoes oyaild large curitinued to be of anexpeditionary nature, generallyundertaken after the eruption hadbegun or the activity .had ceased.

Perhaps. "modeo-N" volcanologybegan in 1912, whb '''"omas A.

ftlaggar, Head of the Geology De-partment of the Massachusettsinstitute of Tectlaology, foundedthe Hawaiian Volcano Observatory(HVO), located on the rim ofKilauea's caldera. Initially sup-ported by an association of Honolulu businessmen, HVO began toconduct systematic and continuousmonitoring of seismic activitypreceding, accompanying, andfollowing eruptions, as well as awide variety of other geological,

A,- -1;4.4. A

.T.-1111

The U.S. Geolegical Survey's Hawaiian Volcano Observatory. op the'crater Alp ofKilauea Volcano. 4 _

. .

40

geophysical, and geochemiobservations and investigati ns.Between 1919 and 1948. HV wasadministered by various Fe erasagencies (National Weather erv-ice, U.S. Geological Survey andNational Park Service), and ince1948 it has been operated c n-tinuously by the Geologica Surveyas part of its Volcano H andsProgram. The more the 60 yearsof comprehensive inv tigations byHVO and other sole Ws in Hawaiihave added substa daily to ourunderstanding of e eruptivemechanisms of Kilauea and Mauna .

Loa, two of theiivorld's most activevolcanoes. Morlsover, the HawaiianVolcano Observatory pioneesdand refined most of the commonlyused volcano-monitoring tech-niques presently employed by otherobservatories monitoring activevolcanoes elsewhere, principally inItaly. Japan, New Zealand, LesserAntilles (Caribbean), Philippines.and Kamchatka (U.S.S.R.).

What does "volcano monitoring"actually involve? Basically, it isthe keeping of a detailed "diary'of the changesvisible end in-visiblein a volcano and itssurroundings. Between eruptions.visible changes of importance tothe scientists would include. markedincrease or decrease of steamingfrom known vents, emergence ofnew steaming areas, developmentof new ground cracks or wideningof pld ones, unusual or inexplicablewithering of plant life, changes inthe color of mineral' depositsencrusting fumaroles, and anyother directly obseritable, andoften measurable, feature thatmight reflect a change in the state

of the volcano. Of coo e, he"diary" keeping dun eruptiveactivity presents ad tional tasks.Wherever and whenever they cando so safely, scipntists document,in words and orf film, the course ofthe eruptiorin detail, maketemperature measurements of lavaand gas,,collect the eruptiveproduct and gases for subsequentlaboratory analysis, measure the_heights of lava fountains or ashply/nes, gage the flow rate of ashelection or lava flows. and k,arryout other necessary observationsand measuren ants to fully docu-ment and characterize the erup-tion. For each eruption, suchdocumentation and data coliectronand analysis provide another build-ing block ins constructing a modelof the characteristic behavior Of agiven volcano or type of eruption.

Volcano monitoring also involvesthe recording and analysis of vol-canic phenomena not visible to thehuman eye, but measurable byprecise and sophisticated instru-ments. These phenomena tnciudeground movements, earthquakes ;-

(particularly those too small to befelt by people), variations itrgascompositions, and deviations inlocal electrical and magneticfields that respond to pressure andstresses caused by the subter-ranean magma movements.

Some common methods used tostudy invisible, volcano-relatedphenomena are based tsins

1, Measurement of changes inthe 'shape of the volcano --vol-canoes gradually swan or "inflatein building up to an "eruptionbecause of the influx of magmainto the volcano's reservoir or

41

1

plumbing system", with the onset,of eruption, pressure is immedi-ately relieved arid the volcanorapidly shrinks or "deflates.- Awide variety of instruments, includ-ing precise spirit-levels, electronicliltrneters," and electronic-laser

beam instruments, can measurechanges in the slope or tilt" of thevolcano or in vertical and hori-zontal distances with a precisionof only a few parts in a million.

2 Precise determinptiort of thelocation and magnitude of earth-

, quakes by a well-designed seismicnetworkas the volcano inflatesby the rise of magma, the enclosingrocks are deformed to the breaking.point to accommodate magmamovement. When the rock ulti-mately fails to permit continuedmagma ascent, earthquakes result.

USGS volcanologiat uses aCorrelation spectrometer(COSPEC) to measure thesulfur dioxide content ofgases elected during theMount St. Helens eruption.

42 .

.1

By carefully mapping out the vari-ations with time in the locationsand depths of earthquake foci,scientists in effect can track thesubsurface movement of magma,horizontally and vertically.

3. Measurement of changes involcanic-gas composition and inmagnetic fieldthe rise of magmahigh into the volcanic edifice mayallow some of the associated gasesto 9scape along fractures, therebycausing the, comppsltion of thegases (measured at the surface)to differ from that usually measuredwhen the volcano is quiescent andand the magma is too deep to allowgas escape. Changes in theearth's magnetic field have beennoted preceding and accompany-ing some eruptions, and suchchanges are believed to reflect

fn.

Ii

temperature effects and or thecontent of- magnetic minerals inthe magma.

tecording historic eruptions andmodern v.,icano-monitoring inthemselves are insufficient to fullydetermine the characteristic be-havior of a volcano, because a timerecord of such information, thoughperhaps tong in human terms, ismuch too short in geologic termsto permit the making of reliablepredictions of possible future be-havior. An integral part of a corn-prehenskve investigation of any

volcano musts also include theft careful, systematic mapping of the

nature, volumes, and distributionof the products of prehistoriceruptions, as well as the deter-mination of their ages by modernisotopic and other dating method§.

--,tResearch on the volcano's geo;logic past extends the data basefor refined estimates of the recur-rence intervals of active versusdormant periods in the history ofthe volcano. With such informationin hand, scientists can constructso-called -volcanic hazards.' mapsthat delineaie the zones of greatest,risk around the volcano and thatdesignate vLithich zones are particu-larly susceptible to certain typesof volcanio hazards (lava flows,ash fall, toxic gases, mudflows andassociated flooding, etc.).

A strikingly successful exampleof volcano research and volcanic-hazard assessment was the 1978publication (Bulletin 1383-C) bytwo Geological Survey scientists,Dwight Crandell and Donal Mulli-neaux, who concluded thatMount 1St. Helens was the. Cascadevolcano most frequently active in

the past 4.500 years and the onemost like.v to reawaken to erupt,"... perhaps before the end of thiscentury." Their prediction cametrue when Mount St. Helensrumbled back to life in March of1980. As of this writing (June1981), the Mount St. Helens erup-tive activity continues and ischaracterized by periodic explo- ,

sive ejection of ash and steamand/or the formation of lavadomes within the crater. Each ex-plosive event may partly or whollydestroy the previously formeddome. i

By analogy to its past history,Mount St. Helens can be expectedto remain intermittently active forYears. possibly even decades, In1980 the Geological Survey estab-lished a facility in Vancouver,Wash., to facilitate the increasedmonitoring and research on notonly Mount St. Helens, bUt also theother volcanoes of the ,CascadeRange, In many ways, the Van -

ever facility can be considered-$ a sister observatory to the

Hawaiian Volcano Observatory.The research being undertaken atboth observatories can' be ex-pected to provide important com-parisons and contrasts between thebehavior of the generally non-explosive Hawaiian shield volca-noes, Kilauea and Mauna, Loa, andthat of the generally explosivecomposite Cascade volcanoes,such as Mount St. Helens, Antici-pated comparative data on whichmonitoring techniques might proveto be most reliable and diagriosticon which type of volcano shouldmaterially enhance our capabilityto forecast volcanic eruptions. I,

Volcanoes and People

Volcanoes both harass and helpmankind. As dramatically andtragically demonstrated by thecatastrophic eruption of Mount St.Helens on it ay 18, 1980, volcanoescan wreak lavoc and devastationin the shor term. However, overthe tong tt-krn and geologic time,volcanic eruptions and relatedprocesses have directly and in-

. air-,:tly benefited mankind; Vol-canic materials ultimately breakdown and weather to form someof the most fertile soils on Earth.cultivation of which hae producedAbundant food and fostered ,

civilizations. People use volcanicproducts as building or road -

..building materials, as abrasive andcleaning agents, an'd'as raw.materials for many chemical andindustrial uses. The internal heatassociated with yOung volcanicsystems has been harnessed toproduce geothermal energy. Forexample, the electrical energygenerated from The Geysers geo-thermal field in northern Californiacan meet the present power con-sumption of the city of SanFrancisco.

The role of the scientists in-volved with volcano research isclear. They must continue to im-prove the capability for predictingeruptions on a longer term as wellas on an immediate-term basis.They must provide the policy-makers and the general public withthe best possible maps of volcanichazards ant# assessment importantfor sound decisions on land-useplanning.

Scientists still do not fully under-stand many of the processes atwork inside the Earth and howthese P:ocesses relate to volcan-ism. What is the ultimate drivingforce for platetectonic move-meat? How and why does magmaoriginate? How do the magmablobs combine to be transpopedto the surface? What are thespecific mechanisms for the for-mation of the different composi-tions of magmas, which in turnform different lypes of volcanoes?Geologists and other geoscienbstsare striving to better answer theseand other basic questions, becausethey know that volcanoes andvolcanic phenomena provide cluesto the Earth's past, present, andpossibly to its future.

References

Although reference works on thetopic of volcanoes abound, this highlyabbreviated and generalized adcountdrawi principally from the followingpublications:

Macdonald, G A. 1972. Volcanoes.Prentice Hall. tnc . Englewood Cliffs.New Jersey. 310 p.

4744) * GewstunazwrpeehTheorn

Tilling. R. I.. 1977. Monitoring activevolcanoes. tri U.S. Geological SurveyYearbook. Fiscal Year 1977, p. 35-40.

U.S. Geological Survey. 1972. Th'eatlas of voicaniciphenomena to setof 20 information sheets illustrating.various volcanic phenomena).

2401 - 361418 133/13s

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_ As the Nation's principal Conservation agency, the Department of the =

Anterior has responsibility for most or our nationally ownetpubliolands and naturat resdurces. This reclides fostarriiiithryirseatlie Orour land and water resources, protecting our fish. and Wildlife,-preserving the environmental and cultural values of our national parksand histortcal placea-and providing for the enjoyment el lite throughoutdoor recreation. The Department assesses our energy an mineral

resources and works to assure that their development is in the best interests csf, all ourpeople. The Department also has a major responsibility for American Indian reservationcommunities and for people who live in Island Territories under U.S. administration.

. _

This publication is one of a series of general interest publicationsprepared by the U S Geological Survey to provide information aboutthe earth sciences, natural resources, and the envirOnment. To obtaina catalog af additional titles in the series "Popular Publications of 1,the U.S.Geotogical Survey," write:

Branch of Distribution or Branch of DistributionUS Geological Survey U.S. Geological Survey604 South Pickett Street Box 26286, Federal CenterAlexandria, VA 22304 Denver, CO 80225