1. No category

SMITHSONIAN"
WARNING:
THIS SET CONTAINS BAKING SODA(SODIUM BICARBONATE)
THAT MAY BE HARMFUL IF MISUSED. READ CAUTIONS
CAREFULLY.
NOTTO BE USEDBY
CHILDREN EXCEPT UNDER ADULT SUPERVISION.
WARNING!
ONLY FOR USE BY CHILDREN
OVER 8 YEARS OLD.
CONTAINS CHEMICALS.
READ THE INSTRUCTIONSBEFOREUSE,
FOLLOWTHEM AND KEEP THEM FOR REFERENCE.
DO NOT ALLOW CHEMICALS TO COMEINTO
CONTACTWITH ANY PART OF THE BODY,
PARTICULARLYTHE MOUTHAND EYES.
KEEP SMALL CHILREN AND ANIMALS AWAY
FROM EXPERIMENTS.
STORE THE SET OUT OF REACH
OF SMALL CHILDREN.
EYE PROTECTIONFOR THE
SUPERVISINGADULT IS NOT PROVIDED.
PLEASEKEEPA NOTEOF OURNAME
ANDADDRESS
DETAILS
FORFUTURE
REFERENCE.
IN EUROPE
CONTACT:
NSI SIMMGAmbH
C~ D76162KARLSRUHE
GERMANY
49-o721-9584-116
PLEASEBE SURETO READTHE ADVISE
FOR SUPERVISINGADULTS
AND THE SAFETY RULES
CONTAINED
IN THIS BOOKLET.
~2002SMITHSONIAN"
INSTITUTION
NATURAL
SCIENCE
INDUSTRIES.
LTD.
910ORLANDO
AVE.
WEST
HEMPSTEAD.
N.Y. 11552
PRINTEDIN USA
ITEMNC,. 3269-08
YOURSET CONTAINS
THEFOLLOWING
ITEMS:
3 VOLCANIC
ROCKS
~
#
Measuring
cup
Note: 1ram,
equals lcc.
VOLCANO SUBSTRUCTURE
SODIUM HYDROGEN
CARBONATE(BAKINGSODA)
BAG
SAND
MIX
ERUPTIONBOTTLE
FORVINEGAR
SAFETY
GOGGLES
~STIC
TUBING
CAUTION: THE VOLCANICROCKOBSIDIAN MAYHAVE SHARPEDGES.
USE CAUTIONWHENHANDLING.
GENERAL
FIRST AID INFORMATION:
IN CASE OF EYE CONTACT:WASHOUT WITH PLENTYOF WATER,HOLDINGEYE OPENIF NECESSARY. SEEK IMMEDIATE MEDICAL ADVICE. IF SWALLOWED:
WASHOUT MOUTHWITH PLENTY OF WATER,DRINK SOMEFRESHWATER.DO NOTINDUCE VOMITING. SEEK IMMEDIATEMEDICALADVICE. IN CASEOF INHALATION: REMOVE
PERSONTO FRESHAIR. IN CASEOF CONTACT
AND BURNS: WASHAFFECTEDAREA WITH PLENTY OF WATERFOR 5 MINUTES. IN CASE OF
INJURY OR IF IN DOUBT,SEEK MEDICALADVICE WITHOUTDELAY. TAKE THE CHEMICALWITH
THE CONTAINERWITH YOU.
ADVICEFOR SUPERVISINGADULTS:
¯ READAND FOLLOWTHESESAFETYINSTRUCTIONS,THE SAFETYRULESAND THE FIRST AID
INFORMATIONAND KEEP THEM FOR REFERENCE.¯ THE INCORRECTUSE OF CHEMICALSCAN
CAUSEINJURY AND DAMAGETO HEALTH. ONLY CARRYOUT THOSEEXPERIMENTSWHICH ARE
LISTED IN THE INSTRUCTIONS.THIS SET IS FOR USE BY CHILDRENOVER8 YEARSOF AGE. ¯
BECAUSECHILDREN’S ABILITIES VARY SO MUCH, EVEN WITHIN AGE GROUPS,SUPERVISING
ADULTSSHOULDEXERCISEDISCRETIONAS TO WHICHEXPERIMENTSARE SUITABLE AND SAFE
FOR THEM. THE INSTRUCTIONSSHOULDENABLE SUPERVISORSTO ASSESSANY EXPERIMENT
TO ESTABLISHITS SUITABILITY FOR A PARTICULARCHILD. THE SUPERVISINGADULTSHOULD
DISCUSS THE WARNINGSAND SAFETY INFORMATIONWITH THE CHILD OR CHILDRENBEFORE
COMMENCING
THE EXPERIMENTS. PARTICULAR ATTENTION SHOULDBE PAID TO THE SAFE
HANDLINGOF ACIDS. ¯ THE AREA SURROUNDING
THE ACTIVITY SHOULDBE KEPT CLEAR OF
ANY OBSTRUCTIONS
AND AWAYFROMSTORAGEOF FOOD. IT SHOULDBE WELL LIT AND VENTILATED ANDCLOSETO A WATERSUPPLY.
SAFETYRULES:
¯ DO READ THESE INSTRUCTIONSBEFOREUSE, FOLLOWTHEM AND KEEP THEM FOR REFERENCE.
¯ DO KEEP YOUNGCHILDRENAND ANIMALS AWAYFROMTHE EXPERIMENTALAREA.
¯ DO STORECHEMICALSETS OUT OF REACHOF YOUNGCHILDREN.
¯ DO CLEANALL EQUIPMENTAND WASHHANDSAFTER CARRYINGOUT THE EXPERIMENTS.
¯ DO NOTEAT, DRINKOR SMOKE
IN THE ACTIVITY AREA.
¯ DO NOT USE EQUIPMENTWHICH HAS NOT BEEN SUPPLIED OR RECOMMENDED
IN THE SET.
¯ DO NOT ALLOWCHEMICALSTO COMEINTO CONTACTWITH THE EYES OR MOUTH.
¯ DO NOT REPLACEVINEGAROR BAKINGSODAIN ORIGINAL CONTAINER.DISPOSEOF IMMEDIATELY.
¯ DO ALWAYSWEAREYE PROTECTION.
GIANT VOLCANO¯ Item #3269
PART ONE: INTRODUCTION
Volcanoesandtheir eruptions are amongthe most inspiring andawesome
expres: ions of the natural world. Volcanicactivity has shapedthe history of the earth andmanyother planets andmoonsin our
Solar System.Whydo volcanic eruptions oocur on so manydifferent worlds? They~11 happenfor the
samereason.Theseworldsare trying to cool off. Theyare hot inside andlosing that ,nner heat to cold
outer space. Volcanic eruptions, whichspewhot lava on the surface or blast hot pure ce, ash, andgas
into the air, are very goodwaysto lose someof that inner heat.
In this manualyou will learn importantfacts aboutEarth’s active andancientvolcanoes,andthe people whostudy them(volcanologists). It also contains suggestionson locating other information on volcanoes. such as maps,videos, booksthat you can borrow from the library, computerf:rograms you can
download
for free from the Intemet, andvolcanosites on the WorldWideWeb,whichwill give you informationon the latest activity at Earth’svolcanoes.
Editorial Note: Importantnewwordsare underlinedthe first time they are introduced. Definitions of
newwordsare in the Glossaryor in the text.
SECTION ONE
Building and Erupting Your Volcano
What you are about to do -- build a
model-- is a glorious undertaking,andoneof the
main ways that scientists and engineers learn
about howthings work. Modelsare not the same
as the things they represent,andit is importantto
understand
the differences. In the caseof the volcano modelrememberthat:
(1) Compared
to real volcanoes,the modelis too
small, steep, andcold. Usea protractor to measurethe slopeangleof yourvolcanoafter it is built.
Youwill probably
find that it is slightly steeperthan
the slope angles of real volcanoesmentionedin
this booklet.
(2) Real volcanoes grow over time: eruption
eruption, layer by layer. Theycan take a few years
to a few million years to develop.Youwill assemble your modelin about ten minutes. The process
ot adding the sand mixture to the plastic frameworkis a formof artistic sculpture,but nothinglike
the growthof a real volcano. After you havebuilt
your volcano, it will take abouttwentyminutesto
dry.
(3) Real volcanoes have undergroundpipes that
bdng_magma
(hot moltenrock) to the surface.
erupt your modelVolcanoyou will first place baking sodainto the center crater andthen adda mixture of vinegarandfood coloring. All of thesematerials arecold.
(4) After real volcaniceruptions,newlava or a_.s.hh
has addeda newsolid layer on the surface of the
volcano. In your model,the magma
is a mixture of
vinegar, food coloring, and bakingsoda. It never
becomes
solid, and doesnot addto the volumeof
the volcano. Youcan dnse your volcanooff in the
sink andmakeanother eruption.
NOTE:
Building anderupting yc ur volcanocan be
a messyendeavorif you are not careful. To be on
the safe side, prepare anderupt your volcano in
the kitchen or a part of the he.usethat doesnot
havecarpeting and/or fine furniture. Don’t wear
goodclothes. Wearan aprono" smockif you have
one. Always wear your protective goggles when
erupting your volcano.
BUILDING YOURVOLCANO
DIRECTIONS
(1) Connectthe tube to the w)lcanosubstructure.
Dothis by turning the plastic substructureon its
side andinserting the 2-foot-long tube fromunderneath into the center hole to ,~ depth of about 13
millimeters(1/2’). Snakethe Jest of the tubing out
through the side of the subst’ucture. Fasten the
tube into the notchedtrack on the din, as shownin
figure B.
figure A
(2) To prepare the volcano-making compound,
you will needa large clean disposablebucket. Cut
the bagof sandmix at one of the corners.Pourthe
mix into the bucket. Next, add9 ouncesor 266CC
of warmtap waterto the bucket,asshownin figure
C. After you add the water, mix the sandandwater
for about 5 minutes or until all of the sand has
mixedwell with the water, as shownin figure D.
(3) Scoopout the compound
with your handsand
apply it to the volcanosubstructure, as shownin
figure B. Apply all of the compound
to completely
cover the entire volcano substructure (except for
the moatthat surroundsthe baseof the volcano.)
As you apply the compound,makea mental note
aboutthe position of the notchesin the plastic substructure’s rim. The compound
mayseema little
wateryat first, but within 5 minutesit will beginto
harden,makingit easier to mold.It is importantto
form a center crater for use later in the eruption
stage. To formthe top part of the volcano,use your
finger to apply the compound
into the upper rim.
Packthe compound
downin the center forming a
wall aroundthe center. After the rim is formed,
maketwo notchesin the rim to correspondwith the
notches on the plastic substructure. Be sure to
affix the tube backin place if it wasdisturbedwhen
forming the upper rim. Thecompound
will take approximately20 minutesto hardenif it is mixedcorrectly.
(4) After your volcano hardens, you maywant
paint it using non-water-basedpaints. Consider
using white to representsnowandice near the top
(see figures #6c and #6d). Greenpaint on the
lower s’,opes can representtrees. After the paint
dries, you can erupt your volcano as manytimes
as you wish.
figure C
figure D
ERUPTING YOUR VOLCANO
DIRECTIONS
(1) Place newspapergenerously into the bottom
of the box from your volcanokit. Placethe volcano
with the hardenedcompound
on top of the newspaperin the box, as shownin figure E. Snakethe
tubing out over the side of the box.
(2) Put your safety goggles on. Preparethe vinegar bottle’s pointy capby snippingat the line with
scissors, as shownin figure F. Besure to point the
bottle downand awayfrom eyes whensnipping.
NOTCHES
figure
figure E
(3) Fill the bottle with household
vinegar (either
red or white will work)as shown
in figure G. First,
measureout 90 ml (3 ounces)of vinegar and pour
into the bottle. Securethe pointy cap on the bottle. Adda few dropsof liquid soapinto the cavity
with the vinegarandgently stir the two. This will
thicken the vinegar and provide for a thick and
foamy eruption. If you want to give the "lava"
color, add several drops of food coloring to the
vinegar. ,~ mixture of three dropsof red andthree
dropsof yellowcomes
closestin color to real glowing lava, but have fun and try someother color
mixtures. Next, add one tablespoon of baking
sodato the center crater of the volcanoas shown
in figure H.
Your eruption time dependso~1 how often you
squeezethe bottle. Onceall o the vinegar has
mixed with the baking soda, you can empty the
"lava’ in the sink andrepeatthe ~ ruption againand
again (always remember
to wea" your safety goggles).
I
.,.,...~_~,
’
figure
fJgure H
figure F
(4) Fasten the free end of the tube onto the
pointy cap of the bottle. Thetube shouldsit firmly
over the endof the pointy cap.
(5) Beforeerupting, checkboth endsof the tube.
Oneend should be exposedin the crater of the
volcano, and the other endshould be fastened to
the pointy capof the vinegarbottle.
(6) Your volcano is now ready to erupt! Gently
squeezethe vinegar bottle to force the vinegar up
throughthe tube whereit will mix with the baking
sodain the crater. Oncethis occurs, the mixture
will flow out of the crater of the volcano,spilling
through the notchesandout over the sides.
figure
G
--
SECTION TWO
What is a Volcano and Whereon Earth are They?
Volcanoesand Plate Tectonics
Earth’s volcanoes are places where molten
rock, or magma,erupts on the surface. At most
volcanoesthe erupted lava, pumice,or ash, piles
up to build a hill or mountain.Manyyoung,active
volcanoeshave the smoothand even majestic profiles that wehavecometo associatewith this word
(see Figure #1). Older volcanoes maybe both
erodedand coveredwith vegetation, hiding their
true nature. Becausethey are not easily recognized as volcanoes,these can be especially dangerous whenthey awakenand erupt.
Whenmagma
reaches Earth’s surface it can
erupt in two basic ways:explosively or non-explosively. Magma
that is rich in gasesblasts apart to
form fragmentsof different sizes, such as pumice
and ash. Magma
that is poor in gaseserupts nonexplosively to flow along the groundas lava. If
magma
cools rapidly, the liquid portion transforms
to naturalg!a,~s.
Most of the volcanoes discussed here
abovesea level, on continents, or islands. These
volcanoes, though, only account for about onefourth of the magma
that reachesthe surface of
the earth.
Theremainingthree-fourths erupts on the sea
floor, mostly along a world-wide systemof mountain ranges called spreadingridge.s. (see Figure
#2). Here, Earth’s tectonic plates are formed. We
knowrelatively little about theseeruptions, which
typically occur about 11/2 kilometers (.93 mi~es)
belowsealevel. At Iceland, a spreadingridge rises
abovesealevel, allowing volcanologi~ststo observe
these eruptions moreclosely.
The world map(see Figure# 3~ showsEarth’s
1,500 volcanoesthat are knownto haveerupted in
the last 10,000 years. Thesedata are from the
Global Volcanism Program of the Smithsonian
Institution, wherescientists keeptrack of Earth’s
active volcanoes.Notice that the active volcanoes
mostly lie in belts that border the Pacific Ocean.
Thesevolcanoesoverlie subductiqq, zones, places
whereone of Earth’s tectonic plates dives beneath
another and descends into the hot mantle (see
Figure#2). As the plate descends,it heatsup. This
drives off sea water that wasaddedto the oceanic
crust shortly after it formedat a spreadingridge.
This hot watery fluid rises into the solid rock of
earth’s mantleabovethe subductingplate. Thereit
causesthe mantlerock to begin melting.
EXPLANATION BOX
The process that generates magmasin
subduction zones is very similar to what
happens whensalt is sprinkled on an icy
sidewalk in the winter. Thewater that rises
into the hot mantlerock, andthe salt added
to the sidewalk ice, both lower the melting
temperatures of these materials below the
actual temperature, causing them to melt.
A third importantenvironment
for active volcanoes is aboveEarth’s hot spots (see Figure #2).
These are columns of unusually hot rock that
extend for manyhundredsof kilometers into the
earth’s mantle, perhapsevet~ to the boundarywith
the core at a depth of 2,885 kilometers (1.79
miles). Thesehot columnsof rock moveonly very
slowly in relation to oneanother.Overtime, as the
tectonic plates moveacross Earth’s surface at
muchfaster rates, the hot spots repeatedly send
batches of _m_agma
upward to build volcanoes.
Oneafter another, volcanoesgrow andare carried
awayfrom the hot spot by the movingplate. In this
way, a linear chain of volcanoesforms, with the
volcanoagesincreasing steadily in the direction
the plate is moving.
Mayon
Strato Volcanoin the Philippines is famous
for its beautifully symmetricalconeshape.Although
this is the classical conception
of a volcano,
in this bookletyouwill seethat volcanoes
actually
comein a widevariety of shapesandsizes. Photo
by Kurt Fredriksson
(Smithsonian
Institution).
Figure #1
EXPLANATIONBOX
Mag.mais the namefor molten rock underground.Magma
consists of two or three parts:
(1) the liquid portion in whichgasesare dissolved,(2) suspended
crystals of variousminerals, andin somecases(3) suspended
gas bubbles.
4
Schematic
moss-section
illustrating plate-tectonic processes.
Threetypesof plate bouncaries
are shown:1 )
divergent (movingapart) boundariesat oceanicspreadingridges, wherethree-fourths of Earth’s magma
erupts virtually unnoticedby humans;
2) convergent(movingtowardoneanother)boundariesat subduction
zones.Thetrench marksthe place whereoneplate beginsto descend
beneathanother..’~’trato volcanoes
are
common
abovesubductionzones;3) transform(movingpast oneanother)boundariesthat join spreading-ridge
segments:
only minorvolcanic eruptionsoccurin this environment.
Alsoshownis anoceanichot spot with its
overlyingchain of shield volcanoes,anda youngcontinentalrift zone,perhapsevolvingto become
an oceanic spreading
ridge. Thelithosphereincludesthe crust (oceanicor continental)andthe rigid part of the under°
lying mantle.Belowthe lithosphereis the asthenosphere,
a region wherethe solid rock of the mantleflows.
Thisflowageallowsmotionof the overlyingplatesto takeplace.
Figure #2
The HawaiianIslands have tile best-known
examplesof hot-spot volcanoes.Theactive volcanoes MaunaLoaand Kilauea lie at the southeastern tip of a 6,000 kilometer (3726mile) long chain
of island and submarinevolcanoesthat has grown
abovea stationary hot spot for morethan 70 million years.
The newestHawaiianvolcano, called Loihi, is
already growingup from the sea floor. Of course,
it is southeastof Kilauea and Mauna
Loa. Its top
is nowabout one kilometer belowsea level.
EXPLANATION BOX
Units: In this section weuse metric units of
length. Equivalent English units are given
below.
Metric System
1 millimeter (mm)
1 centimeter (cm)
1 kilometer (km)
English System
0.039 inches
0.394 inches
0.621 miles
Worldmapshowinglocations for 1,500volcanoesthat haveeruptedduring the last 10,000years. Datafrom
the Smithson~an’s
Global VolcanismProgram.
Figure #3
SECTION THREE
Who Studies Volcanoes and Why?
The scientists whostudy volcanoesare called
volcanologists. Theusual road to becominga volcanologist is to study geologyat a college or univeraity, and then to attend graduate school to
receive additional training andto beginconducting
researchworkfor a Master’s or Ph.D. degree.
Volcanologistsare principally employed
at colleges or universities, and by governmentorganizations, including official volcano observatories
pl~cadnear important active volcanoesin various
parts of the world. The U.S. Geological Survey
runs three volcano observatories located in Hawaii, the Cascades, and Alaska. If you enjoy
nature, hiking, and camping,and are goodat math
and science, you, too, mayoneday becomea volcanologist.
In addition to this geologicalroad to becoming
a volcanologist, each passing year sees moreand
moreimportantcontributions to the study of volcanoes being madeby scientists trained in other
fields. Major advancesin monitoring volcanic
activity have been madeby 9eot)hysi~ists who
study earthquakes and precise changesin the
shape of the land surface that can precede and
accompanyeruptions, Chemists and physicists
have developedinstruments for analyzing
volcanic rocks and minerals and for re-creating
miniature magma
bodies in laboratory furnaces at
high temperaturesand pressures.
Chemistsand physicists also design instrumentsthat are placedon satellites in orbit around
the earth andcan track cloudsof volcanic ash and
gas as winds carry them around the planet (see
Figure #4).
Whystudy volcanoes? On a personal level,
manyvolcanologists wouldanswerthat the work is
fun, fascinating, andallows themto hike aroundin
beautiful settings doingthe workthey love, as well
as getting paid for it! Ona morepractical level,
societies needto understandthe past behavior of
potentially active volcanoesas the best meansof
anticipatingthe effects of future eruptions.LM.onitor~ of these active volcanoes using a variety of
instrumentsis also essential for providing timely
warningfor evacuationsof peoplefrom threatened
areas. Andyou don’t have to live near an active
volcano to be threatened by it! Manyvolcanic
eruptions send denseclouds of gas and ash particles into the air, wherethey drift with the windfor
hundredsand even thousandsof kilometers.
Whenairplanes fly into these clouds they can be
damaged
in a vedety of ways,most seriously when
their enginesingest ash andfail. Sinoe1980mote
than eighty commercial
aircraft haveflown into volcanic ashclouds. Fortunately, all wereable to land
safely. Still, they hadextensive damage,ranging
from scratched windowsto ruined engines. Repair
bills have exceededtwo hundredmillion dollars.
Onthe positive side, volcanoesprove;deheat that
can be tapped to produce elec:ricity
(~
energy). Volcanoesalso help b) form mineral
Satellite imageof the spreadingeruption cloud
fromthe Philippine volcanoMountPinatuboas it
looked4 hoursand45minutesfollowingthe start
of the majorexplosiveeruptionon June15, 1991.
Thevolcanois labeled andb/ack lines showthe
coast of Luzonandother islands. Theimagewas
take~by a weathersatellite operatedby the National OceanicandAtmosphericAdministration
(NOAA).Courtesyof GeorgeStephens(NOAA).
posits that modernsocieties need. For these and
other reasons,the world noed:~voloanoiogists to
pay careful attention to active vol~.oes.
Figure #4
SECTION FOUR
Different Kinds of VolcanoesControlled by the
Three V’s of Magma:Volume,Volatiles, and Viscosity
Volcanoescan be found in a wide range of
shapesand sizes. Whatcontrols the type of vofcenothat develops?In large part the volcanotype
is controlled by three things: the volumeof magma
erupted, the amountof volatiles or gasesit contains, andits viscosi~.
Thelargest explosiveeruptio,~ in recordedhistory,
at the IndonesianvolcanoTambora
in 1815, ejected =J:K)Ut 150 km3 (35.8 miles3) of pumiceand
ash. Somehugeexplosive eruptions preservedin
the geological record, including ones from
Yellowstone Park, ejected morethan a thousand
VOLUME:
In the kitchen we measurevolumes in
units of teaspoons,tablespoons,andcups. At the
gasstation weuse units of liters or gallons. In a
similar way, volcanologists measureerupted volumeswith an appropriate(andreally big) unit, the
cubic kilometer (km3) or (.239 cubic miles). Imagine an enormouscubethat is onekilometer (.621
miles) long on eachof its edges:that is a cubic
kilometer (1 km3) (.239 cubic miles). Volcanic
eruptions range widely in size (see Figure
cubic kilometers (239 miles 3) of pumiceandash.
Thevolumeof magma
invo/ved in an eruption, the
eruption style, and the frequencyof eruptions are
!mportantcontrols on volcanotype.
#5).
Small ones eject lava or oumiceand ash with
a volumethat is just a smallpart of a cubic kilometer. Thelargest lava eruption in recordedhistory,
at the Icelandic volcanoLaki in 1783, produced15
km3 (3.58 miles3) of lava.
VOLATILES:The amount of volatiles or gases
present in the magma
controls howexplosive the
eruption will be. Common
gases in magmasare
water, carbondioxide, suffur dioxide, andhydrogen
sulfide. Whenthe magma
~s deep in Earth’s mantie or crust, the tremendous
pressureof the over.
lying rocks allows these gases to be dissofved
within the liquid portion cf the magma.As the
magma
nears Earth’s surface beneath a volcano,
the pressureis dramatically loweredand the gases
canno longerbe held by t’~e liquid.
YELLOWSTONEISLAND PARK /1~,~,~,,~
/
20Ma
EXPLANATION BOX
Eachtime you hold a sodabottle in your hands
you hold a wonderfulmodelof an explosive volcano that can teach you about the role of
volatiles in magmas.All carbonated drinks
contain carbon-dioxide(CO2)gas. This gas
injected into the soda under high pressure at
the bottling plant andgivesthe sodaits fizz. To
simulate an explosive eruption:
~
~
First
~ ~ VOLUMES
OF ERUPTIVEMATERIAL
Rectangularcubesare scaledto showthe volumes
of pumiceandash ejectedin progressivelylarger
eruptions.. The three largest events showntook
)lace at Yellowstone
NationalParkduringthe last
two million years. [(From: The Yellowstone
Hotspot(1994) by Robert B. Smith andLawrence
W.Braile, Journal of VolcanologyandGeothermal
Research)]
Reprinted
frmmthe Journal
of Volcanology
and
Geotherrna/Research,
v. 61byRohert
B. Smith
andLawrence
W
B~le,
The
Yellowstone
Hotspot,
p. 121-187,
(1994),
withkindpermission
ofElsevier
Science-NL,
Sara
Burgerhartstraat
25,1055
KV
Amsterdam,
TheNetherlands.
Shakethe bottle. This helps gas bubbles to form.
Second Remove
the cap. The carbon dioxide
can no longer be held in the soda
under the new low pressure. In
response, the soda foams and shoots
out of the bottle. Thesamething happens when gas-rich magma"feels"
the low pressure of Earth’s atmosphere and foams beneath a volcano.
It ultimately erupts as an explosive
mixture of pumice, ash, and hot
expanding gases.
starts as seawaterthat is carried into Earth’s mantle by the subducted plate. After the plate
descendsmorethan fifty kilometers (31.05 miles)
into the earth, the seawaterrises fromit to invade
the overlying mantle. This invasion of water causes the mantleto begin melting, andthe watergets
caught up in the magmas
formedby this melting.
In contrast, the magmas
erupted along spreading
ridges and at hot-spot volcanoes are generally
muchpoorer in gases, and these erupt muc.hless
explosively. Their eruptions typically form lava
instead of pumiceand ash.
Figure #5
instead they form countlesstiny bubblesthat
grow larger and larger as the magmabecomesa
moltenfoam. As it erupts, this foambreaksapart
into pumiceand ash particles andthe rapidly expandinggasesthat explosively drive themout of
the volcanic crater. This is the sameprocessthat
you will modeleachtime you erupt your volcano.
Themagmas
formedin different tectonic settings differ in their gas contents and eruptive
styles.
Magmas
erupted in subduction zonesare the
most gas-rich, and subduction-zone volcanoes
have beenthe sites of Earth’s mostexplosive and
deadlyeruptionsduring historical times (see Table
1 on the following page).
The main gas in subduction-zone magmas
is
water, or more properly steam. This water
VISCOSITY:Magmasrange widely in chemical
composition,temperature,amountof crystals, and
percentageof gas bubbles. All of these factors
affect
how easily the magma can flow.
Volcanologistsuse the term viscosity to describe
howrigid a magma
is. Silicon dioxide (SiO2),
silica, is the most abundantchemical component
in magmas.
It also hasthe strongestinfluence on viscosity. Magmas
that are dch in silica are the mostviscous: they are very rigid and do not flow easily.
Crystals andgas bubblesalso increasethe viscosity. Temperaturehas the opposite effect. As it
increases,viscosity decreases.
8
TABLE1
Largest Explosive Eruptions of the 19th and 20th Centuries
Year
Volcano
Location
1991
1991
1982
1980
1956
1932
1912
1907
1902
1886
1883
1875
1854
1835
1822
1815
Cerro Hudson
Pinatubo
El Cnich(Sn
MountSt. Helens
Bezymianny
Cerro Azul/Quizapu
Novarupta/Katmai
Ksudach
Santa Maria
Tarawera
Krakatau
Askja
Sheveluch
Coseguina
Galunggung
Tambora
Chile
Phdippines
Mexico
Washington, U.S.
Kamchatka, Russia
Chile
Alaska, U.S.
Kamchatka, Russia
Guatemala
New Zealand
Indonesia
Iceland
Kamchatka, Russia
Nicaragua
Indonesia
Indonesia
First Historical
Eruption?
Deaths
no
yes
yes
no
yes
no
yes
yes
yes
yes
no
yes
yes
yes
yes
yes
0
800
2,000
57
0
0
2
0
>5,000
> 150
36,417
0
0
5-10
4,011
92,000
All thesevolcanoes,exceptAskja, are locatedabovesubductionzones.All theseeruptior.s produced
pyroclastic deposits
withvolumes
of at least 1 cubickilometer(.239cubicmiles).All but four w~.,rethe first historical eruptionknown
fromthe volcano,andthe highdeathtolls (in heavilypopulated
regions)reflect this fact.
Reprintedfrom Volcanoes
of the Wodd
(SimkinandSiebert, 1994.)
Lavas of unusual silica-poor composition
[40%by weight SiO2)erupted from the Afdcanvolcano Nyiragongocan have extremely low viscosities. Theycan flow downslopeas fast as highway
traffic 100 kilometers/hour (62 miles/hour) and
drain awayfrom the landscapelike flood watersto
leave deposits just tens of centimeters(3.9’s of
inches) thick. Hawaiianlavas have higher silica
contents (50 percent SiO2) and so they are more
v;scous.Still, they can flow rapidly awayfrom the
~ent at velocities of up to 50 kilometers/hour(31
miles/hour) and leave deposits several meters
thtck.
Manylavas erupted from subduction-zone
volcanoes have 60-70 percent SiO2, and can be
very viscous. Theselavas flow very slowly at rates
Of meters, or tens of meters per hour. Viscous
~avasp~le up aroundthe vent forming lava domes
or stubby lava flows that are 50-100meters(54109yards) thick.
EXPLANATION BOX
Wehaveall experiencedthe influence of viscosity in our daily lives. Considerthe difference betweencatsup and cooking oil. Pour
both on a plate. The catsup is moreviscous
andpiles up in a thick mourd, just like silicarich subduction-zone
lavas. Thecookingoil is
~essviscousandflows rapicly awayto form a
thin layer, just like Hawaiiar~lavas. Consider
the difference between ;old cooking oil
pouredona plate andhot cookingoil in a frying pan. Thehotter oil, like a hotter magma,
is less viscous, flows moreeasily, andforms
a thinnerlayer.
SECTION FIVE
Six Volcano Types
In this section wecontrast six majortypes of
volcanoes:
lavadomes,
ci__nder
c__one.__s_,
st__rato
volc__a_noes,.~j_el~_v(;;)lC,~_no~,
calderas,andflood basalt
plateaus. Eachvolcanotype is discussed
9
with regardto the three V’s ()f magma,
anda specific examplevolcano is given. Photographsof
those six examples are ,¢hown in Figures 6a
through6f.
LAVA DOME
Theseform whenviscous, gas-poorlava piles
up arounda vent like toothpaste squeezedfrom a
tube. Most lava domesare the result of a single
eruption or a few closely spacederuptions, but in
some cases dome growth can continue for
decades. Lava domes commonlyemerge on the
flanks of strato volcanoes,or within their summit
craters or calderas - as in the photo of the lava
domein MountSt. Helens’crater (see Figure #6a).
The ThreeV’s:
Volume:low
Volatiles: low
Viscosity: medium
to high
Example: Mount St. Helens, Washington, 19801986 Lava Dome
Height: 270 meters(295 yards)
Diameter: 1000meters (1093 yards)
Volume:0.07 km3 3)
(0.016 miles
°Slope: 30 - 37
Active lifespan: six years
CINDER
Theseare built by cinders falling from an
eruption cloud. Expansionof gases, formerly dissolved in the magma,
drive the eruption. Red-hot
clots of magma
are blasted into the air, wherethey
cool andhardeninto spongycinders. Windcarries
awaythe fine ash, while a hailstorm of coarsecinders falls to constructthe steep-sidedcone,with a
slope angle of 30-34 degrees. Lava flows can
simultaneously erupt from vents near the cone
base (see Figure #6b).
Cinder conescan formsingly or in clusters in
a volcanic field. Theycan also form at summitor
flank vents on strato volcanoesor shield volcanoes,as just oneeventin the growthof theselarger cones.
The ThreeV’s:
Volume:low
Volatiles: medium
Viscosity: medium
Example:Par/cutin, Mexico(1943 - 1952)
Height: 424 meters(463 yards)
Diameter: 900 meters (984 yards)
Volumeof cone: 0.08 km3 3)
(.023 miles
°Slope: 30 - 34
Active lifespan: nine years
Following the powerful explosive eruption of
Mount St. Helens on May 18, 1980, in
Washington
state, a lava domegrewinside the
volcano’snewcrater. Herea helicopter hovers
over the steamingdomein 1984. Photoby Lee
Siebert(Smithsonian
Institution).
Figure #6a
CONE
Paricutin Volcanois a famouscinde~conethat
wasbornin a Mexicancornfield on February20,
1943,as the farmerandhis family watched.It
wascarefully studiedall throughout
its nine-year
lifespan. This photowastakenfrom2 1/2 kilometers(1.55 miles) to the north in March,1944.
The landscapeis buried in ash. Ruggedlava
flows, eruptedfromvents at the northeastbase
of the new cone, are advancing northward.
Photo by Arno Brehme.
Figure# 6b
10
STRATO VOLCANO
Thesesteep-sided structures grow from the
repeated eruption of viscous magma.Gas-rich
viscous magma
can erupt explosively. This blasts
the magmaapart and blankets the volcano’s
slopes with the fragments - ash, cinder, and
pumice. Theseexplosive eruptions are commonly
followed by eruptions of gas-poor magma,which
producethick flows of slowly movingblock lava
(see Figure #13). Thealternation of ash and lava
layers, or strata, gives rise to the name
strato volcano (see Figure
TheThreeV’s:
Volume: medium
Volatiles: medium
to high
Viscosity: medium
to high
Profile of MountRainier Strat.~ Volcanotaken
fromthe east. Theirregular su’nmit wascarved
by glaciersthat still coverthe upperslopes.This
active volcanotowersover th~ nearbycities of
Seattle and Tacoma.
Past eruotions havemelted snowand ice at the summitand produced
dangerous
mudflowsthat rsced downthe flanks
and far out into the lands beyond.Photo by
RichardS. Fiske(Smithsonian
Institution).
Example:MountRainier, Washington
Height abovesurroundings:2.3 km(1.4 miles)
Diameter:8 kilometers(4.96 miles)
Volumeof cone: 86 km3 3)
(20.5 miles
°Slope: 20 - 35
Active lifespan: abouthalf a million years
Figure #6c
SHIELD
VOLCANO
Thesebroad, gently sloped volcanoes (see
F’~gure#6d), named
for their resemblance
to a warriods shield, are formedby repeatederuptions of
~ tluid lava (see Figure #12). Eruptions are
usually non-explosive, and issue from the summit
or from fissures that mayradiate from the summit
or partly encircleit.
Volume: mediumto high
Vo~atiles:low
VLscosity:
Example: MaunaLoa, Hawaii
Heightabovesea floor: 9 km(5.58 miles)
Length.at sea level: 130km(80.73 miles)
3
Volume:65,000 - 80,000 km
3
(15,535-19,120
)
miles
°Slopeon land: 3 - 10
Active lifespan: about600,O00"years
Profile of snow-capped
Mau~la
LoaShieldVolcano, Hawaii,takenfromthe ..=ast. Mauna
Loais
oneof Earth’s mostactive volcanoes.Its last
eruptionwasin 1984.Phot(,by RichardS. Fiske
(Smithsonian
Institution).
Figure# 6d
11
CALDERA
Theseare circular to oval-shaped
collapse
depressions
(see Figure#6e- also Figures#18,
#19 and#20). Theyformwhena large amountof
magma
is rapidly eruptedfrom a hugechamber
underground.Theeruption removessupport for
theoverlyingportionof the volcano,whichcollapses into the void, producingthe caldera.Theyare
common
on strato volcanoesand shield volcanoes,but giant calderaswith diametersof 30-100
kilometers(18.6-62.1miles)cancut acrossa landscapebuitt by saveralearlier volcanoes.
Exceptfor
Aerial viewof CraterLake,Oregon,
lookingtocalderasonshield volcanoes,mostother calderaward
the
east-southeast.
Despite
its
name,
this
formingeruptions are extremelyviolent. They
is a largevolcaniccaldera,formed
about5,700
involve viscous, gas-rich magmas
and produce
B.C.in oneof thelargestexplosive
eruptions
on
toweringashcolumns
anddevastatingpyroclastic
Earthin thelast 10,000
years.CraterLakeis the
flows, ground-hugging
avalanches
of hot ashand
deepest
bodyof freshwaterin theUnitedStates.
gas, Thelargest knownexplosiveeruptionstypiWizard
Islar~l is a younger
conethat grewwithcally produce
large calderas.
in the caldera.Photocourtesyof RoyBailey
(U.S.Geological
Survey).
TheThreeV’s:
Volume:medium
to high
Figure #6e
Volatiles:lowto high
Viscosity:lowto high
Initial caideradepth:1,220meters
(4002ft.)
Presentlake depth:590meters(1935feet)
Example:Crater Lake, Oregon
3
Volumeof pumice’andasherupted: 100km
Caldera
width:8 x 9 km( 4.5 x 5.5 miles)
3)
(23.9miles
Activelifespanof volcanicsystem:about
400,000years
FLOOD BASALT PLATEAU
Thesevoluminousfluid lavas erupt from
swarmsof fissures and cover vast areas. They
includesome
of the largestsingle eru_otiveunits
known.Repeatederuptions over geologically
short periodso| timebuild upthick lava plateaus
with verygentleslopes(seeFigure#6f).
Certainflood basalt provinceshaveagesthat
coincidewith Earth’smajorbiological extinction
events, andmanyscierltists believe that flood
basalteruptions
playeda.critical role in theevolution of life ontheplanet.
TheThreeV’s:
Volume:high
Volatiles:low
Viscosity:low
Example: ColumbiaPlateau, Washingtonand
Oregon
Thickness:
upto 4.2 km(2,6 miles)
2 2)
Areacovered:164,000km
(63,140miles
Volume:175,000km3 3)
(41,825miles
°Slope:lessthan2
Activelifespan:2 - 3 million years
12
Lavasof the Columbia
flood basaltplateaublanket about one-quarter of Washingtonand
Oregon
states. Herea sequence
of the lavas
about150meters
thick is exposed
in thewallsof
Washington’s
PalouseRiver Canyon.
Photoby
DonaldA. Swanson
(U.S.Geological
Survey).
Figure #6f
SECTION SIX
Different Kinds of Eruptions and Volcanic Rocks
Volcanic eruptions can have manydifferent
styles of activity andcan producemanydifferent
deposits. In this section, volcanic eruptions are
discussedin two broadcategories: explosiveeruptions that produce
.mr_roclastic (Greekfor "fire-broken’) deposits of ash, cinder, and pumice; and
non-explosiveeruptions that producelava flows.
A common
pyroclastic eruption style is for the
mixture of hot gases and magr~ato be blasted
straight up fromthe volcanic crater into the air at
speeds that can reach 500 r~eters/second or
1,800 kilometers/hour (5905 feet or 1117
miles/hour) (see Figure #7). In ~helargest explosive eruptions, the cloudscan ri.;e to about50 kilometers(31 miles) aboveEarth’s surface.
Thelargest anddensestpa’ticles are the first
EXPLOSIVE ERUPTIONS
AND PYROCLASTIC DEPOSITS
to fall from the eruption cloud. "~’heseaccumulate
Explosive eruptions are poweredby rapidly
closest to the vent, helping to ~uild the volcanic
expandinggases. Usually those gaseswere once
cone.Thesmallerandless denseash particles fall
at greater distances. Such ceposits generally
dissolvedin the liquid portion of the magma
itsel!
and bubbledout of the liquid as the magma
rose
blanket the landscapeandare ~-alled pyroclasticbeneath the volcano and pressure on the magma fall deposits. Because
the eruption cloudsare carwasreduced. In other cases, hot magma
comesin
ried by the wind, the deposits c~:)mmonly
havethe
shapeof an oval, elongatedir the direction the
contact with water in a lake, as snowor ice, or
underground,with similarly explosive results. In
wind is moving.Thetotal thickr~ess andthe avereither case, the expandinggasesblast the magma age particle size generally decreasewith distance
into fragmentsthat rangefrom car-size blocks to
from the volcano.Oneof the fi’st tasks for volcafine dust, Thesefragments,regardlessof size, are
nologists following explosivevolcanic eruptionsis
called .oy_roclasts, andtheir deposits are called
mapping
the distribution of the deposits.
oyroclastic.
Pyroclastic-fall depositof whib~pumiceandoccasional gray fragmentsof lava. Notethat a rather
narrowrangeof pumicesizes is present. This is
typical of pyroclastic-falldepo,,;its. Fineashparticles werecarried awayby the windto fall at much
greater distances. This depos’l waseruptedabout
15,000years agofrom SanJLanVolcano,Mexico.
A hammer
gives the scale. Ph:)to by James
F. Luhr
(Smithsonian
Institution).
Cerro NegroVolcano,Nicaragua,viewedfrom the
east, duringan eruptionin 1968.Gas,cinders, and
ash are being blastedinto the air. Photoby Tom
Bretz.
Figure #7
13
Figure #8
At a large numberof field stations they describe
the appearance of the deposit, and makemeasurementsof deposit thickness, grain size, color,
andother properties. Theyalso collect samplesfor
laboratory analysis. Because
particles of different
sizes anddensitiesfollow different paths to the
ground,a single exposureof a pyroclastic-fall
deposittypically hasa very limited rangeof particle sizes (seeFigure #8).
Another important mechanismof explosive
eruption producesground-huggingclouds of hot
gas, pumice, and ash celled pyroclastic flows.
Theseare commonlygenerated along the margins
of explosive eruption columns,wherethe air acts
to slow the upwardrise. Manytimes the air wins
the fight, andthe densecloud of gas andash collapses back around the vent and flows downthe
flanks of the volcano. Thesehot, churning clouds
moverapidly downhill at velocities up to 100kilometers/hour(62.1 miles/hour), generally following
stream valleys (see Figure #9). Becausethey
moveso rapidly, andengulf anythingin their paths,
pyroolastic flows are the mostdeadlystyle of volcanic eruption. Becausethey are formedfrom the
entire eruption cloud, Dyroclastic-flow deposits
contain a wide rangeof particle sizes (see Figure
#10). In this way, they can be distinguished from
pyroclastic-fall deposits, which havea muchnarrower rangeof particle sizes (see Figure #8).
Pyroclastic-flow deposit of gray pumicessurroundedby light-colored ash. Notethat a large
rangeof pumiceandash sizes is present. This
is the CampanianIgnimbrite, erupted about
34,000 years ago from a vent just west of
Naples,Italy. "lgnimbrite"is a termfor a particularly densetype of pyroclastic-flowdeposit. The
headof a geologist’s hammer
provides scale.
Photo by James F. Luhr (Smithsonian
Institution).
Figure #10
On the sea floor, low-viscosity magmas
commonly
erupt to form pillow lavas. The hot magma
oozes
out like toothpastefrom a tube andquickly freezes
against cold sea water. This produceselongated
and bulbous pillow shapes (see Figure #11).
Pillow lavas also form wheniava erupted on land
reaches a body of water. Low-viscosity magmas
erupted from volcanoes on land, such as Kilauea
and MaunaLoa in Hawaii, commonlytake on two
forms. Pahoehoelava has a braided, ropey form,
whereasaa has a spiny texture (see Figure 12).
Both pahoehoeand aa types can also be found
amongsea-floor lavas andat subduction-zonevolcanoes. In the latter environment,however,viscous lava moreoften movesas very sluggish jumbles of large andsmall blocks. This is called block
lava (see Figure #13).
A pyrodasticflow racesdowna streamvalley on
the southflankof ArenalVolcano,CostaRica, on
July 13, 1987.Thesehot churningcloudsof gas,
pumice,andashmoveat speedsup to 100kilometers/hour (62.1 miles/hour). Theyare the
most deadly type of volcanic phenomenon,
destroying everythingin their path. Photoby WilliamG. Melson(Smil~sonian
Institution).
Figure #9
NON-EXPLOSIVE ERUPTIONS
AND LAVA TYPES
Gas-poor magmas
erupt to form lava flows.
Lava occurs in four maintypes: Dillow, Dahoehoe,
aa, andblock.
14
Pillow lavas photographed
froma researchsubmarinenearthe summitof Loihi Volcanoon July
20, 1988. Thesepillows lie about 1 kilometer
(.621 miles) belowsea level atop the youngest
active volcano in the Hawaiianchain. Photo
courtesy of HawaiiUnderseaResearchLaboratory.
Figure #11
These1972lavas on Mesouth flank of Kilauea
Volcano, Hawaii, showsa lava in the backgroundand pahoehoe
lava in the foreground.
Thewidth of the photo is 4 meters(13 feet).
Photoby RichardS. Fiske(SmithsortianInstitution).
This19911ok)cklava flow fro’n ColimaVolcano,
Mexicois a jumbleof fresh igray andangular)
andoxidized (red androughMocksof various
sizes. Thehammer
is 30 ce ~timeters(11 inches) long. Photoby ,JamesF. Luhr(Smithsonian
Institution).
Figure #12
Figure #1 ~
SECTION SEVEN
Eruption Forecasting and Prediction:
Successat MountPinatubo (Philippines) in 1991
I1 youlive near a volcano, you wouldprobably
wantto know:When
will it erupt? Will lave or ash
comeour way?. Howoften will it happen?Will we
have to leave our home?Whencan we go back?
Scientists monitoringvolcanoescannotforetell the
future, but with intensive efforts they can provide
long-term forecasts andshort-term predictions of
likely future eruptive behavior.Howdo they do it?
By monitoring the volcano with various instruments, through basic geological studies in the
field, andby analysisof the historical eruptivepatterns, forecasts can be done.
This is the sameapproachyour medical doctor takes in monitoring your health. Your doctor
uses insVumentsto take your temperature,listen
to your heartbeat, and take your blood pressure.
Yourdoctor also asksabout the history of diseases
in your family, all in anattemptto keeptrack of your
health prior to diagnosisandtreatment.
The 1991 eruption of MountPinatubo in the
Philippines (see Figure #14) providesan excellent
casestudy of successfulvolcanotogicalprediction.
Based mainly on scientists’
warnings, some
250,000peoplesafely evacuatedbefore the maior
June15 eruption. This section tells you the story
of monitoringefforts at MountPinatubo.
For as long as the oldest villagers could
remember,MountPinatubo had been quiet. Then,
on April 2, 1991, peoplewere startled to see an
explosionof steamand ash from a vent on the volcano’s northeast flank (see Figure #15). Within
15
~(;’~
~
~
~ [XPLANATION
~apsho~ngcenUalluzon~lan~in ~e Philippines,andthem~ation
of MountPina~bo
and
ot~rvo~anoes
~athaveerupled
in thelast
million
years(Pli~ene
toQuaterna~).
The~anilatre~hma~t~ l~ati~~erethe Eurasian
Platebeginsto su~ucte~ardbenea~luzon
and ~e Philippine
SeaPlat~.~is suUd~tion
zoneg~erat=
~e magmas~hateruptin luzon.
Cou~esy
of Christopher
G. Ne~all(U.S.Geological
Su~ey).
Figure #14
days, scientists from the Prilippine Institute of
Volcanologyand Seismologyinstalled a portable
seismoq_raDh
just west of Pinatubo. Morethan 200
volcanic earthquakeswere recorded in its first
twenty-four hours of operation
Basedon their field andlaboratory studies,
scientists prepared a volcanic-hazards mapthat
showedthe course of ancient pyroclastic flows
(see Figure #16). Somehad reached Clark Air
Force Baseand nearby densely populated areas.
HAZARD
ZONES
~ ~’~
I~ Pyroclastlc-flow
- ~’~[~t~~ ,,,~=
¯
I~JPyroclastlc-flow
buller ~’- ".
Volcanic-hazardsmapdistributed on May23,
1991by the Philippine Institute of Volcanology
andSeismology
andthe U.S. GeologicalSurvey.
Patterns showzonesexpectedto be affected by
pyroclastic flows and mudflows.Dashedlines
showactual distribution of pyroclastic-flowdeposits following the June15, 1991,eruption,
whichmatches
well with the pre-eruptionhazard
zones.Courtesyof ChristopherG. Newhall(U.S.
GeologicalSurvey).
Alignedcraters on the northeastflank of Mount
Pinatubo.Theseformedon April 2, 1991,as one
of the first warningsigns of the majoreruption
that took place21/2 months
later onJune15-16,
1991.Thevents in the foregroundare inactive,
but thosein the background
are still steaming¯
Photo by Christopher G. Newhall (U.S.
GeologicalSurvey).
Figure #16
Figure #15
Earthquakedetection is an essential part of
volcanomonitoring. Before an eruption, rocks can
crack as they are pushed apart by’ ascending
magma.Seismometers detect this cracking as
earthquakes. At manyvolcanoes the numberof
earthquakesincreasesbefore a large eruption.
Alerted by the earthquakes,scientists recommended
evacuation of everyonewithin a 10 kilometer(6.21 mile) radius of the summit.
A teamof scientists from the Philippine Institute and the U.S. Geological Surveyset up seven
seismic stations. Theserecorded 50-90 earthquakes each day through May 10. Data were
processedat Clark Air Force Base, a major U.S.
facility at the easternfoot of the volcano.
Volcanologistsquickly beganfield studies at
MountPinatubo. They sought to establish its
record of past eruptions. This is an essential step
in monitoring active volcanoes. The scientists
were shockedto find huge deposits from earlier
explosive eruptions, the youngestjust 500 years
old.
16
Scientists also developeda warning scheme
withfive levelsof alert andsentit to publicofficials.
Usinga telescope-like optical instrumentsensitive to sulfur dioxide (SO2)gas, volcanoiogists
detected a ten-fold increase in SO
2 emissions
from summitsteamvents during May13-28, a sign
that magma
wasrising towardthe surface.
In early Junethe focal point of mostearthquakes shifted 4-8 kilometers (2.4-4.9 miles)
northeast, to the region beneaththe steamvents.
~ - a continuous,
rhythmic
vibration
associated with movementof magma
was detected, along with a drop in SO
2 flux.
Scientists also installed twoelectronic tiltmeter~ near the active steamvents. Theseinstrumentsmeasurechangesin the groundsurface that
can be caused either by the movementof magma
below or by pressure from released gases. The
tiltmeters recorded a bulging of the upper east
flank.
This wasfollowed by eruption of a lava dome
Below,a typhoonraged, a’~d heavyrains trigjust north of the most vigorous steamvent. Begeredmudflowsthat swept thr(=ugh several towns
tween June 7 and 11, the lava domedoubled in
anddestroyedmanybridges. After June 16, activsize. Eruption of this lava domeconfirmed the
ity decreased
in intensity, but a.,,h eruptionscontinexistence of an active magmaticsystem- a storued until September2. The June 15-16 eruptions
age area and channels through which magma formeda caldera near the top ~f MountPinatubo,
could movethrough the upper crust to reach the
about 21/2 kilometers(1.55 mil~s) in diameterand
surface.
more than 650 meters (213;! feet) deep (see
In the daysof early June,scientists raisedthe
Figure #18). The floor of the new caldera was
alert level to a 3 and then to a 4. When
the lava
abo~t 800meters abovesea I,~vel, roughly 1,000
domeappeared,they issued a red alert - level 5.
meters (3280 feet) below the summitof the volOnJune 10, Clark Air Force Basewas evacuated canobefore the eruption.
andaircraft valuedat onebillion dollars wereflown
The eruptions and later mudflows, spawned
tosafety.
as the new loose ash and pumicedeposits were
On June12,duringPhilippine
Independence stripped away by rains, buried some100,000
Daycelebrations,
thefirst
ofa series
ofpowerful homes
andaffectedthe liveliho x~of over a million
eruptions
blasted
an ashcolumn
to 19 kilemeters persons. Muollows continued to be a problem
abovesealevel(seeFigure
#17).Moreeruptions, manyyears after the 1991eruption.
pyroclastic
flowsandearthquakes
followed,
and
still,
theworst
wasyettocome.
Viewof the new2-kilometero (1.2 mile-) wide
caldera of MountPinatubo,looking from above
toward the south on August1, 1991. A small
explosionhasjust occurred.Photoby Thomas
J.
Casadevall
(U.S. GeologicalSLrvey).
MountPinatuboeruption cloud of June12, 1991
rises into the atmosphere.Photo taken from
Clark Air ForceBase,20 kilometers(12 mi!es)
east of MountPinatubo. Photoby DavidHadow
(U.S. GeologicalSurvey).
Figure #18
Figure #17
OnJune14 an infrared video cameraat Clark
Air ForceBaserecordeda sudden,zipper-like passage of brightness (heat) across the upper east
flank of Pinatubo,whichvolcanologistsbelievedto
be a fissure vent opening.
The maineruption, the secondlargest of the
century, beganthe following day. Pyroclastic flows
swept nearly all areas covered by prehistoric
deposits of a similar type, blanketing about 100
km2 (38 miles2) (the dashedline on Figure 16).
The eruption columnmushroomed
to heights of 40
kilometers (24.8 miles), well into the trt~.
17
Abouteight-hundredpeopledied in the eruption, mostly from pyroclastic flows, mudflows,and
post-eruption disease. However,tens of thousandsof lives were savedby the monitoring and
warningefforts of scientists andgovernment
officials.
Comparethe volcanic-hazards maddevelopedfor MountPinatuboprior t¢ the June15 eruption with the actual results of :he 1991eruption
(see Figure #16). Theclose similarity is a graphic
demonstrationof the successof volcanologists’
efforts at Pinatubo.Unfortunatgly, volcanologists
rarely havethe benefit of ext,=nsive and costly
monitoringandfieldwork neededfor reliable forecasts andpredictions.
SECTION EIGHT
SomeCommonQuestions about Volcanoes
(1) Whatis an active volcano and how manyare
there?
A volcano should be consideredactive if it
has the potential to erupt again. But howcan you
tell whena volcano has finally becomeextinct?
There is no easy way. Oneapproachis to assume
that a volcanois not likely to eruptagainif it hasn’t
had an eruption in the last 10,000 years.
SmithsonianVolcanologistslist about 1500volcanoesthat eruptedon land or in shallowwater during that time, shownin Figure #3. About 540 of
these volcanoes have had historically reported
eruptions. Eachyear, 50-70 volcanoeserupt. As
you read these words, about 15 of Earth’s volcanoesare probablyerupting.
(2) Whatwasthe largest volcanic eruption of the
last 100,000years?
The eruption that producedIndonesia’s gigantic Tobacaldera (see Figure #19) about 74,000
years ago is the largest nowknown. It ejected
about 3,000 km3 (717 miles3) of pumiceand ash,
roughly 3,000 times as muchas MountSt. Helens
ejectedin 1980.
(3) Are fewer people dying from volcanic disasters nowthan in the past?
"Natural calamitystrikes at aboutthe time
whenoneforgets its terror."
- Japaneseproverb
Eventhough scientists have an ever-deeper
understandingof volcanic processes, this knowledgehasnot yet led to a decline in eruption-related deaths.
From1900 to 1986, the average numberof
humandeaths from volcanoes per year was880;
Landsatsatellite photo of the Tobacaldera,
Sumatra,Indonesia.Fourseparatelarge explosive eruptionshavetakenplace herein the last
1.2 million years. Thepresentcaiderais 100kilometers (62.1 miles) tong and30 kilometers
wide.It formedduringthe youngest
of the eruptions, 74,000yearsago. LakeToba(black) covers morethan half of the caldera.Dataacquired
in May,1987.
Figure #19
morethan from 1600to 1899, whenan averageof
620 people per year died in volcanic disasters.
Although the numberof deaths caused by posteruptionstarvation hasdeclinedin this century,the
numberassociated with pyroclastic flows and
mudflowshas increased.
A major reason is that global population has
increaseddramatically in recent centuries - many
morepeopleare living near dangerousvolcanoes.
Manynations lack the money,scientific resources,
or political will to monitortheir volcanoes.
TABLE 2
The ten most deadly eruptions in history.
Volcano
Tambora
Krakatau
Pelde
Nevadodel Ruiz
Unzen
Kelut
Laki
Kelut
Santa Maria
Galunggung
Year
1815
1883
1902
1985
1792
1586
1783
1919
1902
1822
Country
Indonesia
Indonesia
Martinique
Colombia
Japan
Indonesia
Iceland
Indonesia
Guatemala
Indonesia
Deaths
92,000
36,417
29,500
23,080
14,524
10,000 (?)
9,350
5,110
4,500 (?)
4,011
All volcanoes except Laki are located above subduction zones. Data from Volcanoes of the
World (Simkin and Siebert, 1994).
18
In addition, peopleliving near long-dormant
volcanoesmaybe unawareof the threat in their
backyards. Field and laboratory studies of past
eruptions, instrumental monitoring, improvedcommunications, and public education are neededto
savelives.
(4) Whatare the ten mostdeadlyeruptions in his-
tory?.
Of the ten mostdeadly eruptions in history,
listed in Table2, all but the IcelandicLaki eventin
1783 occurred in a subduction zone. Theseare
sites where descent of an oceanic plate into
Earth’s mantle carries seawaterinto the zone of
melting. As a result, subduction-zonemagmas
are
rich in water, andexpansionof that wateras steam
near the surface drives the explosive eruptions
that makesubduction-zonevolcanoes so dangerous.
Volcanoespose a variety of hazards. Many
humandeaths are caused directly by erupted
materials, most commonlywhenpeople are engulfed by fast-movingpyroclastic flows. Duringor
even long after an eruption loose ash and other
debris can be sweptup by currents of flood waters
to create destructive mudflows. Wheneruptions
occur in the sea, they can generatetidal waves,or
tsunami, which can devastate coastal areas far
from the eruption site. Of her deathsare causedby
earthquakes, lightning, disease, and starvation
associatedwith eruptions.
(5) Whatwas the largest explosive eruption
historical time?
Thelargest historical explosive eruption took
place in 1815at TamboraVolcano, on Indonesia’s
Sumbawa
Island. The Tamboraeruption ejected
about 50 km3 (31 miles) of magma,which translates to about 150 km3 (93 miles) of pumiceand
ash. An estimated 10,000 people were killed
directly, and another 82,000died as a result of
starvation anddisease.Theeruption left a circular
area of collapse, called a caldera, about6 kilometers in diameter at Tambora’ssummit(see Figure
#20).
Theash and volcanic gasesinjected into the
upper atmosphereby the Tamboraeruption formed
a globe-encirclingcloud that filtered the sunlight
andaffected Earth’s weather. Theyear 1816, following the Tamboraeruption, has beendescribed
as the "Year Without a Summer." In North
Amedca, records of the Hudson’s Bay Company
show that the summerof 1816 was amongthe
coldest ever recorded. Unseasonably strong
winds from the north and northwest brought three
major episodesof frost in early June, early July,
and mid-August.
19
NASA
spaceshuttle photograph
of Tambora
Volcano, Indonesia, and the 6.5-kilometer (4.03
mile) widecalderamarking
its ;ummit,left by the
1815eruption. This wasthe largest explosive
eruptionin historicaltime.
Figure #20
Thesefrosts reachedas fa- south as Philadelphia, PA, and Trenton, NJ, causingpoor harvests
and food shortages. In Europe, the summerof
1816was exceedingly wet an( cool. This dismal
summeris credited with having inspired Mary
Shelley to write Frankenstein~mdLord Byron his
somber poemDarkness, whi,’h was written in
June, 1816, on the shores of Lake Geneva,Switzerlan~A short portion is reprinted here:
Darkness
I hada dream,whichwasnot ~ II a dream.
The bright sun wasextinguish’d, andthe stars
Did wanderdarkling in the eternal space,
Ray/ess,andpathless, and the icy earth
Swung
blind andblackeningin ’he moonlessair;
Morn cameand went - and came, and brought no
day,...
Lo,’d Byron
(6) Howdo volcanoes benefit mankind?
Although most discussions of volcanoes focus on their destructive qualities, volcanoesalso
play manypositive roles in our lives. Theair we
breatheandthe water wedrink originally wascarried to Earth’s surface in volcanic eruptions.
Volcanicrocks are usedall over the world as construction materials and building stones. Magmas
ponding beneath volcanoes h~,lp to concentrate
copper, silver, gold, andmanyother metals that
our society dependsupon. Volcanic heat is tapped
to generate electricity in manygeothermalareas
around the world. For example, Reykjavik, the
capital city of Iceland, has near y 100,000people
andgets 70 percentof its heat ;.nd hot waterfrom
wells drilled into hot volcanicro(k.
The Geysersgeothermalarea in northern California generatesenoughelectricity to meetthe needs
of two million people. Volcanoesalso
benefit agriculture becausesoils developed
on volcanic rocks are extremely fertile. Volcanic ash
falling fromthe air canact as a naturalfertilizer.
SECTION NINE
The Three Volcanic RocksIncluded in this Kit
This set contains three small volcanic rocks
for your rock collection: pumice, obsidian, and
basalt. Usea magnifying glass to observe them
closely. Find a placewith bright sunlight.
DIRECTIONS
PUMICE:
Thewhite to gray rock is pumice, which
consists of about 95 percent natural glass and 5
percentcrystals of quartz (silicon dioxide: SiO2).
Quartzhas a grey color and you should be able to
see a crystal or two with your magnifier. Youmay
also see a few dark spots. Theseare rare crystals
of magnetite (iron oxide: Fe304). The glass
pumiceforms a sponge-like network, signifying
that it contains a lot of emptyholes nowfilled by
air. Some
of the larger holes are obvious on the
surface of the pumice, but manyothers are too
small to see. Becauseof all these holes, pumice
feels light. Morecorrectly, it is less densethan
other rocks. Dropyour pumicein a glass of water.
It floats! All that trapped air makespumiceless
densethan water. If you leave the pumicesoaking
in water long enough,the water will eventually
seepin to replacethe air andthe pumicewill sink.
Youcan alwaysdry it out in the sunor an ovenand
dothe trick again.
crystals. In this case, though,the glass doesnot
have a sponge-like texture, and the crystals are
mainly plagioclase, a silicate mineral containing
sodium, calcium, and aluminum. Obsidian forms
from viscous, silica-rich magmas
that havelow gas
contents. Becausethese magmas
are so viscous,
atomscannot easily migrate to growing crystal
faces, andtherefore few crystals develop,instead
the liquid solidifies as glass. Obsidian is well
knownfor the wayit breaksalongcurvedfractures.
Early humanstook advantageof this feature and
learned to form razor-sharp blades and arrowheadsfrom obsidian.
BASALT:
Thedark gray rock with the dull finish is
basalt. This lava contains abundantsmall crystals
of olivine, andpyroxene,two silicate mineralsthat
are rich in iron and magnesium.
Thesewill appear
as small reflecting spots under the magnifier.
Basalt forms from magma
that is poor in silica and
has low viscosity. Basalt is the mostcommon
volcanic rock on Earth. Under the sediment on the
oceanfloor is a layer of basalt lava about2 kilometers(1.24 miles) thick. Hawaii and other volcanic islands are giant mountainsof basalt that
rise up fromthe seafloor.
OBSIDIAN:
The shiny black rock is obsidian. Like
the pumice,this obsidian also consists of about95
percent glass and 5 percent
PART TWO:
BOOKS AND EDUCATIONAL REFERENCES
Volcano & Earthquake, by Susanna Van Rose,
1992. A Dorling-Kindersleyb~)okpublished in the
U.S. by Alfred A. KnopfInc., NewYork anddistributed by RandomHouseInc., NewYork, 1992. (A
richly illustrated book written for teenagersto
adults.)
Volcanoesof the World, by TomSimkin and Lee
Siebert. Geoscience Press, Phoenix, 1994.
(Smithsonian
compilationandinterpretation of data
about Earth’s volcanoes; rich in maps, photos,
drawings, andespecially data; written for a wide
audienceas well.)
20
ABOUT VOLCANOES
Volcanoes, by SeymourSimon. Morrow Junior
Books,NewYork, 1988. (A short, illustrated book
wdttenfor children ages8-12.)
Mountainsof Fire: The Nature of Volcanoes, by
Robert W. Decker and Barbara B. Decker. Cambridge University Press, Cambridge,U.K., 1991.
(A well-researchedgeneral treatmentof volcanoes
with abundantdrawingsand photographs;written
for a wide audienceranging from high school studentsto professionalvolcanologists.)
LOW-PRICED, EDUCATIONAL VOLCANOMATERIALS
This DynamicPlanet
A full-color wall map,1 meterby 11/2 meter
(3.3 feet by 4.9 feet) (revised in 1994)that should
be on the bedroom
wall of everychild interested in
our planet, its volcanoes,earthquakes,meteorites,
andplate-tectonic activity. This eye-pleasingwodd
mapusescolors to designateelevation. Superimposedon it are:
¯ Locations of over 1500volcanoesactive dudng
the last 10,000years, plotted in four agecategories.
¯ Locations of over 24,000 earthquakes,largely
from1960- 1990,plotted in three magnitudecategories andtwo depth ranges.
¯ Locationsof 139meteoriteimpactcraters.
Also includedare:
¯ A three-dimensionalcross section of the earth
illustrating its majorzonesof volcanoes
andearthquakes(a color versionof Figure2 in this section).
¯ A text treatmentthat givesa primeron plate tectonics, volcanoes,and earthquakes.This wonderful mapcosts only $7.50 ($4.00 per mapplus
$3.50 per order for postage and handling). Orders shouldbe sent to:
USGS
Information Services
Federal Center, Box 25286
Denver, CO80225
Specify "DynamicPlanet’ and makecheck or
moneyorder in USdollars payable to "Interior
Department- USGS’.Within the United States,
mapsmayalso be ordered using a credit card by
calling toll free 1-800-USA-MAPS.
Irmide Hawaiian Volcanoes
This 25-minute color video was producedin
1989by the late Maudce
Kra’ft, in collaboration
with the Smithsonian Institution and the U.S.
Geological Survey. It is narrated by RogerMudd.
This video goes beyondthe t,eauty of Hawaii’s
surface eruptions and takes you deep underground where you will learn about the underground magma
plumbing systP, ms. It contains
spectacularviewsof lava founta,nsandflows, scientists at work, as well as rare ~ady20th century
footageof early eruptionsandscientists.
Awarded
5 Stars by the Journal of Geological
Education "If you buy only one video about
Hawaiianvolcanism,this should be the one.’
A teachers’guide (22 pages)is ~tlso available.
contains questions and answer.,; relating to the
video, as well as three laboratoryexercises.
The video costs $20. Please. specify VHSor
VHS-PAL
format. The teachers’ guide costs an
additional $5. Makecheck or moneyorder in US
dollars payableto SmithsonianI,~stitution. Only
pre-paid orders are accepted. Purchaseorders
cannot be accepted.
Pleasesendorders via postal mail to:
RichardS. Fiske
Museum
of Natural History MRC119
Smithsonian
Institution
Washington, DC20560, USA
ELECTRONIC ACCESS TO VOLCANO RESOURCES
Programsto Downloadand
Run on your Computer
SEISMIC/ERUPTION
This programoffers a woddmapand a variety
of regional and local mapsthat showearthquakes
and/or volcanic eruptions in time sequencesince
1960. Earthquakesare shownby circles and volcanic eruptionsby triangles. Thesizes of the symbols indicate the size of the earthquakeor erup,
lion. Colors indicate the depth of the earthquake
or the type of eruption (lava, ash or both). When
an eruption occurs, the nameof the volcano is
shownnext to it. This is an extremely engaging
program,that dramaticallyindicates that our planet
is alive.
21
Segments
of this programare used throughoutthe
Smithsonian’s new Geology, Gems.and Minerals
exhibit in the National Museum
of Natural History.
The programwasdevelopedby Ala’~ Jonesof the
State University of NewYork, Bing’~amton,using
earthquakedata from the U.S. Geo.ogical Survey
anderuption data from the Smithsonian.It is well
worthyour effort to retdevethis program.
Note that this programonly works on IBMtype computers,Current(9/96) reqL irements are:
Windows
3.1, Windows
95, or IBM0-3/2. To download this programfollow thesesteps:
DIRECTIONS
Point your webbrowserto:
http://www.geol.binghamton,
edu/facu~ty~ones
To load the Windows
3.1 version:
(1) Openthe WindowsFile Managerand select
File/Create Directory. In the windowthat pops up
type: "c:/volc" andclick "OK". This is a temporary
directory that can be erasedwheninstallation of
the Seismic/Eruptionprogramis complete.
(2) In the browser, scroll
down to the
seisvole.readme
link for information regardingthis
program.
(3) Click on the seisvole.zip link to downloadthe
Seismic/Eruption program. A "Save As" dialogue
box should appearin the "directories" box. Goto
c:/volc andclick "OK".
(4) A "Saving Location" box will appearshowing
status of the download.It maytake awhile to save
because
the file is 4.4 Mbin size.
(5) Files with the .zip suffix are files compressed
with the PKZIPprogramand needdecompression.
At the time of publishing (9/96) PKZIPwasfreewareandcould be obtainedover the Internet at the
following
address:
http://www.yosemite,net/help/win31_pkzip.html
If this addressis no longer valid, performa
web search using PKZIPas the key word and go
to a site that has the program.
(6) Follow the instruction for downloadingPKZIP
anddecompress
the seisvole.zip file. Makesure to
use the -d option. For example,at the DOSprompt
type:
pkunzip-d seisvole.zip
(7) From the WindowsProgram Manager select
file/run/browse, go to c:/volc/setup.exe,click "OK"
and follow the dialog on screen to completethe
installation of the Seismic/Eruption
program.
ERUPT
This programallows you to design a volcanic
landscapeas it builds up in cross section on the
screen. The user choosesthe eruption types, the
location of the vent, and other parameters
suchas
wind speed.
The programcan be steppedat any time and
a neweruption type selected. In this wayone
gains an understandingof howa volcanic terrain
growsthrough the accumulationof deposits from
various eruptions. The program was created by
Kenneth Wohletz of the Los Alamos National
Laboratory. Note that this programonly works on
IBM-type computers.
To begin, point your webbrowserto:
http://geontl .lanl .gov/page1/directory/wohletTJeru
pt.htm
There you will find options for downloading
different versions of ERUPT.
Detailed instructions
are given below for loading the Windows
3.1 version.
(1) Openthe WindowsFile Managerand select
File/Create Directory. In the windowthat popsup
type "c:/erupt" andclick "OK".
(2) In the browserselect the version for Windows
3.1 currently version 2.0 - named"er20-16". A
"SaveAs" dialog box should appearin the directories box. Goto c:/erupt andclick "OK".
(3) A "Saving Location" box will appear showing
status of the download.It maytake a while to save
because
it is 2.6 Mbin size.
(4) In File Manager
go to c:/erupt anddoubleclick
onthe file there. Thiswill start the installation.
(5) Click "Setup"to unzip the files andget to the
"Erupt 2.0 Setup" screen.
(6) Followinstructions andinstall to the "Erupt 20"
directory.
(7) In File Manager, select c:/erupt, then
File/Delete to removedirectory. Click "OK" then
"Yes".
(8) In ProgramManager,openthe group in which
you wantthe Erupt icon to reside.
(9) Do File/New. Click "ProgramItem" button and
then "OK".
(10) A "Properties Dialog" box will appear.Fill
as below:
Description: Eruption
Command
line: c:/erupt20/erupt.exe
Click "OK"
(11) To start ERUPT,
double click on the volcano
icon that appearsin the window.
SITES ABOUT VOLCANOESON THE WORLD WIDE WEB
Bulletin, a monthlyreport of all volcanicactivity on
the planet.
This is the sameinformation read by professional volcanologists aroundthe world to find out
newsof recent eruptions. A list of Earth’s 1500
vo}canoesknownto have erupted during the last
10,000years is also given along with basic informationfor each. This site contains an extensive
set of links to other sites aroundthe world, organized by region.
Welist only four sites, but eachcontainslinks
to manyother volcanosites aroundthe world.
Smithsonian’s Global Volcanism Program
http://www, volcano.si.edulgvp/
This program is devoted to the study of
Earth’s active volcanoes.Hereyou will find the latest issues of the Global VolcanismNetwork
22
Volcano World
http://volcano.u nd.nodak.edu/
Thisis a site devotedto educatingschoolchildren and visitors to U.S. National Parks and
Monuments
about volcanoes. It is run out of the
University of North Dakotaand funded by NASA.
VolcanoWorldincludesmodernand near real-time
volcanoinformation, with extensiveuse of remotesensing imagery. Under their section Learning
About Volcanoesare the topics: Ask a Volcanologist, andVolcanoFacts.
Michigan Technological
University HomePage
http://www, geo.mtu.edu/volcanoes/
This site containslots of volcanoinformation
and imagesabout recent and on-going eruptive
activity.
Particular emphasisis placed on volcanohazardsmitigation, remote-sensingof volcanoes
and eruption clouds, and histor cal eruptions of
Guatemalanvolcanoes. It also includes a geographiclist of individual volcano~ageswith eruption reports.
U.S. Geological Survey:
CascadesVolcano Observatot’y
http://vulcan.wr.usgs.gov/home.html
The CascadesVolcano Observatory is focusedon the eruptive history ant hazardsof active
volcanoesin the CascadeRang~,which runs from
northern California,
through Oregon and
Washington,and into British Columbia(Canada).
This site provides a wealth of information about
thesevolcanoesas well as excellent generalinformation about volcanic features and phenomena,
volcanic hazards, and volcanc monitoring techniques.
GLOSSARY
sa lava: (ah-ah) a form of lava, common
on Hawaii, with a rough surface and spiny protrusions
(see Figure #12).
ash: the smallest solid particles producedby an
explosiveeruption, definedas less than 2.5 millimeters(3/32 inches) across. Ashparticles include
glass and crystals from newly erupted magma
as
well as ejected fragmentsof older rocks.
block lava: a type of lava, commonly
erupted in
subductionzones, that movesas a jumble of separate blocks rangingfrompebblesup to the size of
small houses(see Figure #13).
caldera: a cimutar to oval-shaped depression,
generally more than 1 kilometer (.621 miles)
across, formedby collapseof a pre-existing volcano or volcanic terrain (see Figures #6e, #18, #19
and #20). Rapid eruption of magmaempties an
undergroundcavity, into which the land surface
collapses.
cinder: an inflated volcanic fragment with a
sponge-like texture. Innumerableholes are surroundedby thin films of glass andembedded
crystals. Theterm cinder is usually usedfor dark-gray
to black (silica-poor) fragmentsthat cannotbe broken by hand. Pumiceis used for lighter-colored
(silica-rich) fragmentswith similar sponge-liketextures, that can be brokenby hand.
cinder cone: these small volcanoes are conical
piles of cinder that accumulatearounda vent as
particles fall from an eruption cloud (see Figure
#6b).
23
cote: the central portion of the earth, madeof
metallic iron. It beginsbeneatl"the silicate mantle
at a depthof 2,885kilometers~ 1,791miles) below
the surface. Theouter core is liquid andextendsto
5,145 kilometers (3,195 miles). There the solid
iron inner core beginsandreachesto the center of
the earth at 6,370kilometers.
crater: a circular to ovaloshal:eddepressionat a
volcano, generally less than 1 kilometer (.621
miles) across. Craters form aroundan eruptive
vent by accumulationof material or by explosive
removalof material.
crust:the outermostlayer of the earth, lying above
the mantle. Continental crust can reach 70 kilometers (43.4 miles)thick. Oceanic
crust is upto 10kilometers(6.2 miles) thick. R~x:ksof the crust are
less densethan those of the mantle, andthus the
crust "floats" onthe solid mantle.
density: a physicalpropertyof a matedalthat indicates its massper unit volume.Imaginea cube, 1
centimeter(25/64inches)or~ a side. If filled with
water, it wouldweigh 1 grambecausewater has a
density of 1 gram(.036 ounces)per cubic centimeter (25/64 inches). If you saweda rock into a cube
the samesize it wouldweighabout 2.7 grams(.09
ounces), becausemost common
rocks have densities of about 2.7 grams(.09 ounces)per cubic
centimeter.
dormant:sleeping; a dormantvolcanois one that
is not presentlyeruptingbut is considered
likely to
doso in the future.
eruptiveunit: the deposits left by a single eruption. Geologistsmapthesein the field anddistinguish oneunit from another.
flood basalt plateau: gigantic flows of fluid, nonviscous lava erupt from swarmsof fissures and
spread over vast areas. Repeatederuptions over
geologically short periods of time build up thick
lave plateauswith very gentle slopes (see Figure
~3f).
forecast: an eruption forecast is a statement
aboutfuture eruptiveactivity that is less specific
than an eruption prediction. Typically forecastsare
basedon recordsof past eruptive activity andconcern events that are months to decadesin the
future. As volcanologists continue their reseamh
efforts, eruption forecasts maybecome
increasingly specific andevolveinto predictions.
geophysicist:
a scientist whoapplies principles of
physics to geological problems. Geophysicists
measureearthquake waves, gravity, magnetics,
andelectrical currents, among
other parameters.
geothermal:
refers to earth’s inner heat. Geothermal areas are usually located in regions of young
volcanoes, where heat from cooling magmas
can
easily reachthe surface.
glass:natural volcanicglassis the liquid part of a
magma(molten rock) that has been quickly
"frozen" (cooled and solidified). If magmas
cool
more slowly, they have time to grow crystals
insteadof formingglass.
harmonic
tremor: a continuous, rhythmic type of
earthquake wave caused by magmamovement
underground. Harmonictremor can be an important warningsign of an eruption in the nearfuture.
hotspot: a relatively stationary plumeof hot solid
rock that rises fromdeepin the earth. Partial melting abovehot spots builds volcanoes, which are
carried awayby the movingtectonic plates at
earth’s surface. This conveyor-beltprocessforms
linear volcanic chains called "hot-spot chains"
(see Figure #2).
lava: magma
that erupts non-explosivelyand flows
as a liquid. Rocksformedwhenthe flowing liquid
solidifies are also called lave. Consultthis glossaryfor definitions of different lavetypes:aa, block,
pillow, and pahoehoe.
lava dome:a thick moundof viscous, gas-poor
lave that piles up arounda vent like toothpaste
squeezedfrom a tube (see Figure #6a).
magma:
molten rock below ground. It consists of
crystals and gas bubbles suspendedin a liquid
portion.
mantle:the silicate portion of the earth that lies
betweenthe crust and the core.
24
monitoring: to observe and measuresomething
that changesover time.
mudflow:a densemixture of water and rock fragments that flows rapidly downstream channels
with the consistency of wet concrete. The enormousenergy of mudflowscan carry themtens of
kilometersacrossflat landsat the foot of a volcano
before they cometo rest. Theseare very destructive phenomena
that can crush bridges and bury
towns.
pahoehoe
lava: (pa-HOY-hoy)
a type of fluid, nonviscous lava with a smoothto twisted, ropey surface. As the fluid lava oozesdownhill, its skin
cools, solidifies, andwrinkles,while its molteninterior continuesmoving;(see Figure#12).
pillow lava: a type o lava that resemblesa stack
of pillows. Thesepillows develop whenhot magma
erupts into cold wat~=r and oozes forward as a
series of bulbous masseswhosecrusts immediately freeze to glass ~seeFigure #11).
plagioclase:a silicat.,= materialcontainingsodium,
calcium, and aluminum.
plate tectonics: see tectonic plate andFigure #2.
prediction: an eruption prediction is a detailed
statementabouteruptiveactivity in the nearfuture,
just hours to a few weeksaway. A prediction
shouldspecifythe tirre of the eruption,the location
of the eruptive vent 3n the volcano, the eruption
style (explosive or rlon-explosive), andits size.
Less precise statements about future eruptive
activity are called for~,asts.
pumice:an inflate(I volcanic fragment with
sponge-like texture. Innumerableholes are surroiJndedby thin films of glass andembedded
crystals. The term pumiceis usually used for whitegray fragments(silica-rich) that can be broken
hand.Cinder is usedfor darker, moresturdy fragments(silica-poor) with similar sponge-liketextures.
pyroclast: greek for "fire broken." Describesa
fragmentof any size producedby an explosive volcanic eruption, including ash, andpumiceas well
as larger blocks and bombs.
pyroclastic fall: exp!osivevolcanic eruptionsgenerate clouds of hot gas, ash, and pumice. This
term describesthe p-ocessof thesesolid particles.
falling to the ground,wherethey form"pyroclasticfall deposits" of put, ice or ash with a restricted
rangeof particle siz~.s (see Figure#8).
pyroclastic flow: in someexplosive eruptions, hot
clouds of gas, ash, and pumiceflow along the
groundat high veloc ties like an avalanche.These
are amongthe most destructive volcanic phenomena. Whenthese c ouds cometo rest they produce"pyroclastic-flow deposits", chaotic
mixtures of ash, pumice, and rock with a wide
rangeof particle sizes (see Figure #10).
seismograph:an instrument that records earthquakewaves.Motionof the groundis detected by
a seismometer,either attached to the seismograph
or far away. The earthquakewavesare recorded
as a set of wiggly lines on paperor on a computer
screen.
seismometer:
an instrument that detects ground
motions caused by earthquakes. Modern seismometers
detect motionsin three separatedirections, onevertical andtwohorizontal.
shield volcano: broad, gently sloped volcanoesnamed
for their resemblance
to a warrior’s shield are formedby repeated eruptions of very fluid,
non-viscouslava, whichcan flow far from the vent
(see Figure #6d).
silica: the chemical componentsilicon dioxide
(SiO2) is the major componentof most volcanic
rocks on earth, ranging from less than 40 percent
by weight to morethan 75 pementby weight. The
amountof silica in a volcanic rock is one of the
parametersused in assigning it a name,such as
basalt or andesite.
spreading ridge: mountain ranges on the sea
fk:xx whereearth’s tectonic plates are spreading
apart and growingby symmetricaladditions of new
igneousrocks on both sides. It is estimatedthat 75
percent of the magma
that reachesearth’s surface
erupts at spreadingridges (see Figure #2).
stratosphere:
the secondlowest portion of earth’s
atmosphere.At the baseof the atmosphere
is the
troposphere, whereall weathertakes place. The
tropospherevaries in thicknesswith latitude, from
- 9 kilometersnearthe po~esto 16 kilometers(9.9
miles) at the equator.Aboveit is the stratosphere,
a regionof dry, thin, cold, clear air that is 32 kilometers (19.8 miles) thick. The stratosphere
includes earth’s ozonelayer, at 19-48kilometers
(11.8-29.8 miles). The ozone layer blocks the
sun’s ultraviolet rays, whichwouldotherwisemake
life on our planet impossible.
strato volcano: steep-sided conical volcanoes
that grow from the repeated eruption of viscous.
magma.Explosive eruptions of gas-rich magmas
produce layers of pumiceand ash. Eruptions of
gas-poor magmas
send out short, thick flows of
block lava. Oneafter another these two processes
build the cone(see Figure #6c).
25
subductionzone: an arcuat~ zone on Earth’s surface whereone tectonic plat,~ descendsbeneath
anotherandis resorbedinto tte mantle. Theseare
sites of abundantlarge earth ~uakesandbelts of
explosive volcanoes(see Figu-e #2).
tectonic plate: oneof the apl: roximately20 independentlymovingsegments
of earth’s outer shell.
Theyinclude the crust andthe upperrigid portion
of the mantle. Thesetwo lay~,rs form the lithosphere, or "rocky sphere" (see F gure #2) and have
a thickness of 100-200kiiomet~,rs (62-124miles).
Tectonic plates are formedat ~~ceanicspreading
ridges and consumed
at subdu(,tion zones. They
moveatop a flowing layer of .,;olid mantlerock
belowcelled the asthenosphere
see Figure #2).
tiltmeter: an instrument that can detect tiny
changesin the slope of the ground. With a networkof tiltmeters installed arounc’a volcano,geophysicistscanmonitorinflation an,~deflation of the
cone. Such motions can be ass,)ciated with the
movementof magmaundergrounc.
vent: a crater or fissure at the earth’s surface
through which magma,steam, and old rock fragmentscan erupt.
viscosity: a physical property of licuids that measureshowrigid they are. Waterha:~low viscosity,
whereashot tar is very viscous. Ma~mas
similarly
showa rangeof viscosities that affect the waythey
erupt.
volatiles: gaseouschemical components,such as
steam,carbondioxide, hydrogensul=ide, and sulfur dioxide. Thesecan dissolve in rr olten silicate
liquids underhigh pressure, but at low pressure
they convert to gas. Rapid expansionof this gas
drives explosiveeruptions.
volcanic-hazards map: a map that indicates
areasthat are likely to be affectedby variousvolcanic events (lava flows, pyroclastic llows, pyroclastic falls, mudflows,etc.) during f~iture eruptions.
volcanologist: a scientist whostudies ,’olcanoes,
volcanic rocks, or volcanic processes.
volume:Here this term refers to the quantity of
magma
erupted, measuredin units of cubic kilometers(kin 3) (.239 miles3): a gigantic c:Jl:~ easuring 1 kilometer (.621 miles) on a si~e.
THE SMITHSONIAN INSTITUTION
The SmithsonianInstitution is hometo morethan 141 million objects, ranging in
size from insects and diamondsto locomotivesand spacecraft. It is the world’s
largest museumcomplex, comprising 15 museumsand galleries and the National
Zooin WashingtonDC, and two additional museumsin NewYork City. Millions of
visitors each year visit the nation’s capital to view such treasures as the Hope
Diamond,the Star SpangledBanner,and the WrightFlyer. A broad range of exhibits
ensures a fun and educational experience for Youngand old alike.
Oneof the world’sleadingscientific researchcenters, the Institution has facilities in
eight .states and the Republicof Panama.Researchprojects in the arts, history and
science are carried out by the Smithsonian all over the world. Someof the
Smithsonian’sresearch centers include the Srnithsonian Astrophysical ObserVatory
in Cambridge,Massachusetts, the Smithsotlian MarineStation at Link Port, in
Florida, and the SmithsonianTropical ResearchInstitute, in Panama.
For membership
informationof pre-visit planningmaterial, write or call the Visitor
Informationand Associates ReceptionCenter, SmithsonianInstitution, Washington,
D. C., 20560, (202) 357-2700(voice), (202) 357-1729(TTY). Youmayalso
the Smithsonianthrough our website, www.si.edu.
HISTORY
JamesSmithson(I765 -1829), a British scientist, drewup his will in 1826nam)~g
his nephew, Henry JamesHungefford, as bene~ciary. Smithsonstipulated that,
should the ~ephewdie without heirs (as he did in 1835), the estate wouldgo to the
United States to found "at Washington, under the name of the Sr~ithsonian
Institution, an establishmentfor the increase and diffusion of knowledge...’,
OnJuly 1, 1836, Congressaccepted the legacy bequeathed to the nation by James
Smithson,and pledgedthe faith of the UnitedStates to the charitable trust. In 1838,
fOllowingapprovalof the bequest by the British courts, the UnitedStates received
Smithson’s estate--bags of goMsovereigns--then the equivalent of $515,169.
Eight years later, on August10, 1846, an Act of Congresssigned by President James
K. Polk, established the SmithsonianInstitution in its present formand Providedfor
the administration of the trust, independentof the governmentitselE by a Board
Regentsnnd Secretary of the Smithsoni~n.