3. VOLCANIC HAZARDS AND REsPONsEs

a) Distribution of volconic octivity : Different Dlqte boundories

{ Volconism refers to the(\<t,< fi i(+h1<, (.(tlt

1a(ht s( i|l tlv o,l\t"A a tfhNft

{ There ore obout 600 hi5toaicolly qctive volconoes oround the world

{ World drslflbution oF vol.onrc oclivity. Corrvergent plate l:oundor rcs: $!Ja

- Oceonic crust vs Oceantc crustOceanlc crust rs Contutenta/ crust

- Divergenl plote boundonies: 15,/o- Oceantc crust vs O.eanlc crusf- Continenta/ crust ,s Conttnenla/ cturt

- Hot Spots: $ty

m1i

,5iiEt

'.lii?"li" + u*'SrcrLi*rc+ rl'd nel

I I l]'Uqarld3 .l4n/a:.0.qap+.yi, '., .i,h jl*c".", enir*-r1cco-t.a-l .- t.rua,r, s.rela\-,-,-r' t-.,- . w sr.*t, 3aepagos Lcurdl

]r* ?t* ,,Yt',;1"*,i:::."" '%","'- . "Y' ^lic0ofid

:-_ _

\: PiJ t"'haracet s' h ' ',1rl's INen ls,'r" ,.I!lt.^'zei[.o ! "-

.ft{xrr S.rhild4t votcan,cAcrrvny oe€pten tS

Bw"{a b.2ifi 6!'E {lt E 118:€ 18r l.{t'!{ 100,1u at"?l 20,-l

lNPrrrFr !i rr i,rr,!

Figu.e 49: World dist.ibution of Volconoes

6l

+ There ore two woys thot volconic oclivaty con be meosured. Type of lovo produced> Eruptive style (,e: woy in which ihe lovo is extruded on to lhe eorth's surfoce)

+ the type of volconrc oclrvrly rs

boundories in which thev ore foun{.closalv ossociofed w'th rhe rypes of plole

i0rvirgtn{ ir.1,.i..:iiLl....'?$or1'1llic

t

1) Lovo: Types of Lovc ond Volconoes

The nolure qnd types of volconic londforns thol ore formed depend r-rpon how

goseous ond how VlJaotrl5 the lovq is when it reoches the eorlh's surfocell^ogmq: molten.ock lhot is found beneoih the Earth's surfaceLovo: rnolfen rock thot is extruded fron volconoes ond volconic fissures

lLrl\r{tqe.l+,'t A ndrsili c? (hyolil;,

JNon-eXllolivr ) trplosiv e

lovo

+ There ore three moin types of lovq: Bosaltic, Andesitic ond Rhyolitic+ Lovo type depends on silico conlent, woier content, gcs content ond mogmc

temperolure{ The relotive violence of volconic eruptions depends on the lovq type{ The types of lovo ond volconoes thof formed ore closely ossocioted with the types

of plote boundqries in which thev ore found:-g Divergent plote boundory .O Convergenf plote boundory

lovo

vijrosily- l)clr& 0F ft1istancL to {iowI,illttr funper"lut ( -la,N(. r)istAtiTv

f )c1l.y r <lli., ( ct+J.^+ --lA;rl\/,- vi:ru>ify

Volconic octivity

61

i) Basallic Lava (olso known qs'bosic lovo')I Produced by the upword movenenl of mdteriol from ihe monile+ High in mognesiun (Mo), qnd Iron (Fe)

"i Mofic composition: low silico content (45%-54%)+ Temperolu.e ; 1000"C to 1200"C{ Low vascosity (degtee of tesislonce fo flow) i.e. flow quickly

. Longer time to cool ond solidify

. Flows over lorger oreos os rivers of molten rock

. Form volconoes with gentle slopes e.g. shield volconoesI Associoted with guiet/ ge^Ile,but fregL,ent eruplions! Found olong mid-oceon ridges, over hotspois ond olongside rift volleys+ 3 types of bosoltic lovo - pillow lavo, Pdhoehoe ond AAt The iype of bdsoltic lovo found in hot spofs differs frorn those in divergent plote

boundories

Pillow Lcvo Pohoehoet Elongoted,

int ef aonnect edflow lobes lhoi oreellipticol or circulorin cross section

{ More viscous, slow

noving lova thot hos

lqvo

{ Low viscosity, fluid lovothol solidifies into odastinciive ropy texture

utdet wolet ar ice

blocky surfoce

goseous bo5ollic

+ Formed rn hot, low-silico,bosolJic lov(r

Do note that pahoehoe nay develop tnfo aa furfhef downslope as the lava cools ondslows down However. aa does not develop into pahoehoe.luhile both ferns |vere cotned fron studtes of Hawaiion to/csnoes, they do notapply to jusl Hawaiian volcanoes

l-. Some types of volconoes ossocioted with bosolfic lavc flow inclqde:-

Q Shield yolcanoes. Brood, mossive, gently sloping volconoes. Lorgest volconic londforms on Eorfh. Formed by highly fluid bosqltic lavo which trovel qreot distcnces before

solidificotionBuilf of numerous overlopping lovo flows extauded f.om o centrol ventE.9. Mouno Loo, Kiloueq in Howoii

'L surfoce cool5 rapidly toform o glcssy surfoce whileiova below is sfill coolingond flurd enough io flow

!

65

Q Fissure volcanoes. Also known os lovo plqteou. Brood ploins or ploteous. Formed by the exfrusion

or flood

of guiet

bosolfs

lovo flowscenlrol venis

. Bosolfic in nature

. E.g. Aeimoey (Icelond); 6ioni's

ihrough fissures rofher thon

(Northern frelond); DecconCcusewoyPlcteou (Indio)

TYI)ES OF

Figure 50 rypes of volconoes

ii) Andesitic Layg (olso known os 'ocidic' or 'intermediote lavo')

-! Results fl"om lhe process of subduction where oceqnic crusf is being dest.oyedhence, found ot volcqnic ond islqnd orcs (convergent plcte boundories)

I fnlermediote composition : hos hagher silico content (53,62%).l Temperalu.e : 800"C to IOOO'C

. High viscosrty - flow slowly. Tokes o shorter crarounf of time to cool. Thick lovo f lows. Flow over less areo of lond, thus prodLlcing steep-sided. less spreod,ouf

feotures{ Less frequent, bll violent efttptions (gos build-up due to high gos confent). wifh

osh, rocks. gos, steom and lovo

66

* It should be nofe.1 that andesitic /ava is usual/y bundled togethet wifh rhyolitic lova.The difference between the fwo is sna//, bul rhyolillc lava t5 much nore vtscout thanandesilic lava, and may thus resulf in nore vtolent erupfions.

CLASSIFICAIION & FLOW CHARACTERISTICS OF

Hfryolile

Sllica (S{od conlenl

EruPilod telnperatureLa% color sa e in "C:

sffi

Mobi{ily ol lava flows

voLcAfitc Focrc

Volclnlc rdck nane

1160"C

i Dec.easing mobilily of lava -->

Figure 57. Chaftcterisrics of bosoltic, ond€satic ond .hyolitic lqvo

iit Phyglilic Lala

Iron (Fe) * Silico (Si) ) Felsic composiiion r 70 to 7B% silrcoTemperoture : 600'C fo BOO"C

Exfremely high viscosiiy flow very slowly. Solidify quicklyHigh qos content

+{

!

.t

Couse explosive eruptions becouse its high sjlico content results in exlremely highUi5aorit'/ (resistonce fo flow); clso associoted wilh highly violeni fephrqond pyrocloslic flowFound ot conve.gent plote boundoriesRhyolitic lovo would olso erupt from oveT continenfol hotspots (for exomple,Yellowstone in Wyoming).Types of volconoes offen ossocioted wrth sndesitic oa rhyoItic lovo flowr,

Sfralovolcanoes. Also known os composile volcoiloes. Steep-sided conical nounfoin. Cornposed of stroto (loyers) of pyroclostic debris & lovo flows. Andesitic or rhyolitic in notLtre

Eauptions more explosive viscous lovc & high gos pr'essurePorositic cones rnqy be builf on the flonks of the volcono. This occurs whenthe moin vent is blocked by hordened lovo

61

. In the next eruptron, the mogmo reoches the surfoce by b.onch pipes,creoting dykes within the volcono

. E9. Mount Fuji (Jqpon); Mount 5t Helens (USA); Mt Moyon (Philippines)

Q Lavo Domes. Sleep-sided convex cone. Formed when ondesitic or rhyoliiic lovo solidifies on exposlre io the qrr or

neor the crqter. E9 Mt Pelee (Mqrtihique)j Mono Croiers of Colifornio (USA)

Types of Volcanoes

FiEre 52 -fypes of Volcdnoes

ltllu

very lrquid lava, noss verywidespread, efr itled lrom aolunb a R'ver Pislea(

Lrqurd lala emrtted fron acentral venli large, s6delimerhas a collaFse cardera

Lar.h l.,,l.unlarn, Mo!nlSVr!atua, Hrgh ard Aurle, :t4t#

Cinder Corc

Expld!v€ liqqiir lava, sr0rl,emilt€d nom a cenlrar v..1,n.ortrnued ron!l erou!lh. n.r,r'burld uF a shrc d volcanl

,1ni. Llharibenarn Hill,P rll B rlto, Larr Bltle, 'zN-.-

rvlDre !lscous iavns, nLIheip.tive (p!ro.rrJt.) d4tini1a.9e, enillcd fron a r:-pnrrar

Rr { rrr t10!.1 5l Helent -uN=:F- =Vciy rrs.!Lrs avr, r. !rr.jer'r

sda l, ca. be erplo.rve...nidronl! d.cuis adla.eni locrdors or.odfos ta vlrrrnors

i,1,r!il La.Jen. 5h3nrn3, M=. ={!{1f-:- --

Caldera

very arge composile vor.anocollafsed aRer an exFroivepenod; neq!enlry astdciried

'l.it-!r Lakr, N!,{beiiy,Ki:r.a. Long vatt€!, - ti'J

-,=t *It!Y.4si-=

68

2) fypes of Volconic Eruptions{ Volconoes con be clossified occording fo their eruptive style which is bosed on

the degree of violence of the explosion, which is offected by the pressure ondthe onount of gos an the mogmo

Non-exDlostle erupfiQlrs fcelondic qnd HqwoiionExplostve erupfionS Sfrornbolion, Vulconion. Vesuvion, Krqkotoon, Peleon, Plinion

o) Icelondic+ Lovo flows gently from o fjssuret- Very fluid bqsoltic mognq gives olmost horizontol flows

b) Howdiiqn+ Lovo is emilted genlly from o vent{ Produces shield volcqnoes

c) st.onbolionI Smoll buf frequent erlptions occuaI Spo.odic erupfions of gos

d) Vulconion{ More violent ond less frequentt Viscous lovo which ropidly solidifies

't Hos o violenf explosion qffer d long period of inoctivityI Violent expulsion of mogmo cho.ged with gos

f) KrokotoonA Hos an exceptionolly violenf explosion thot moy remove much of the oriqjnol

g) Pevoh+ Very highly viscous lovo results in blockage of moin veni+ Lovo chorged with gos escopes weqk points+ Violent eruption is dcconpdnied by py.oclostic flows ihot moy include o nud.e

ordenle ('glowing cloud')

h) Plinion+ Lorge explosive events thol form enormous dork columns of lephro ond gds

high inlo fhe strotosphere (>11 km).1- Lorge omounts of lovo ond pyroclqstic moteriols ore ejected

69

:'er :t

. .,. r, r",-r_-.J1,!,.i!, ,r,)",rit ( r*,

Figure 53. Types of Volconic Eruptions

VEI

2

3

6

7

I

€

g.

o.1kn3 @

5 {-1km3)

(-1.ooc km3)

Figu.e 54 Relotionship of VEI with volune

ffiw.

of lephro emission

10

Volcqnic Explosivify Index Clossificotioh

,Q4ptss 3477

Vulconion/(5ub Plinion)

Vulconion(5ubPlinion)/Plinion

Plinisn

Plinidn/UIiro Plinion(Krokoloon)

I

t,,,,

sevete .yeorly

cotqclysmic l 10 y.s

poroxysrnol : 1OO yrs

lNevodo rielKIJI Z

6qlunqgunq 278

5i. Helens 84

Krokotoo 39colossol

I

:

: 1OO yrs

:

.

7 Ullro-Plinron/(Krqkotoan)colossclSUper-

4

71

b) Effects of volconic eflrptions: Hozo.ds AclZctfd - Thrpql

{ Ncturol hozords result fron noturol processesi ond oreenvironmentol disost€rs c{I{tsed by humon octivi}y ondmismondgernent

lo hunor, lifr qrrd

dtfferent ftom f IJY(/ ly

environmenlal

! A volconic eroption is d noturol process lhot is considered os o qeoloqichozord onlv when if Doses donqer ond serioqs risk 10 people ond DroDerty both closeio ond for owoy from the volcono.

There ore severol hozords ossocioted with volconic eruptions:

3) Pyro./dstrc flows4) Valconic 6ases5) AftnBpherrc Effects

F'9 57. some Volcon'c Hozords

1?.

1) Lava Flows

Type:I Bosoltic, andesitac or rhyolitic in noture't Comnon in less explosive eruptions (eg. Howoiion ond fcelondic eruption

types).l Rorely life lhreotening{ Move slowly, giving people tirne to escope

Effecls:-L Con couse gteat environnentol & property domoge

Eg: Stnce 1983, lavo flows of Kilouea buned roads and destroyed structures in the Ka/apanoarea on lhe southern coost of Howoi

z) l ep!ry

Type:+ 6reoi amounts of tephro ore produced by explosive eruptions{ Tephro refers to moteriol lhol is eiected from o volcono during on eruplionI Tephro includes oirborne lovo frogmenfs & pyroclosts (osh, lopilli, volconic

bombs, scorio, pu{1ice); glossy porticles-l Vo.ies fron sond,sized porficles (volconic osh) up to boulder-sized pieces of

ropidly cooled ond solidified lovo (volconic bornbs)

--, \5h.LZ,y.tf. lapilt,._ 6 2-bq nu

t Cqlse struclu.ol domoge (e9 roof collcpse), mechonicol fqilures of engjnesin vehicles & oirplones

I Couse respirqiory probl€rnst Deslroy vegeiolion.l Reduced visibilify ond confominote wofer systems

',1h1Nc\lt( . Cr{tmlE9 1: 198? eruption of aalunggung, rndonesia - osh clouds reduced power n the jetengines of 2 Boetng 747jets, resultng in power/ess descents of 2600m fhe engines andexfet.ior surfaces of the jets suffered extensive danage due to nelting of ash, abraston

E9 2: 1973 eruption oa Heinaey rsland off Icetdnd - Tephro falls and lava i.tows covered3.2 kn'? of the village of VestndmaeyJar d over 3OO structures were destroyed

73

fype:

3l Pyroclastic Flows

Volconic moferidl fhoi trovels ropidly neor theovolonche of hot gos, ash, pumice ond rock frcAmentsAlso known os nule ordente (glowing cloud)Occur when eruption columns or lavo domes ofvolconoes collopse (Fig 58)

{

ground surfoce os cn

ondesitic or rhyolific

{ Temperqtq.e ronges beiween 700 ond 1000'C{ Trovel ot high velocities > 100krn/h.+ Moy exlend verlicolly from o volcono's summit or directed loferolly trom o

v/€ok oreo on the fldnk of the cone

Effects:{ Most dongerous ond life-th.eotening hozord os it engulfs ond burns

eve.ything olong ils poth

Eg 1: /Uount PeEe, /Uartinigue (8 llay 19Oz) nude ardente trave/led to the city af Stherre at ftAkn/hr ond ktlled 30,OO0 people

Eg 2: I'lount Unzen, Japen, 1993 colapslng dorne coused nurncrous pyroc/astic f/ot1/srhat ki/led over a dazen pcop/e

E9 3: Mount r'lerapi (Novenber 1994) Done col/opse generated nude ardentes thatfesulted in 60 cdsualtlet, .1e,'truction of vi/loges and farnland. cast )t nttl/ton dollor; inloss* and destrucflon of 9 5 knt? of fordt

1

| '-'*"-"

'f9- in r\at eatr''tt to cclunt

-r..:'j"; , ath -c)a trqe

I i---- "-a,,,

, n'"I

Figure 59- Py.oclosticttf Unzen in 1993

su.ge at

Figre 58.

generatedsurge is

14

4l Volcohic 6ases (sotne of which (e Doisonous)

Type:'1 Emitted in both genlle ond explosive eruptions+ Mostly woter vopour+ Othet goses include corbon dioxide, sulphur dioxide, sulphur trioxide, corbon

rnonoxide, hydrogen sulphide, hydrogen f luoride-{ Volconic fog (vog) is formed when sulphur dioxide gos is converted to

sulphuric ocid+ Lovo entering seowoler reocts with sewcter to forn hydrochloric ocid

beoring lova hoze'| Vog ( volconic r smog) ond lcvo hoze obsure scenic vistos

Effecls:+ Lower ogriculturol yields for certoin crops{ Aflect people with respirolory or heort conditions

Lg: In 1986, /orge anounts of CO, enissian fron Lake Nyos ia Caheroon kiled nore thanlTOO people 6nd 3oOO coft/e

5) Atmospherlc Effects

l) Lowerrng of globa/ tenperature.l DusT, volconic ash & goses {e g sulphur dioxide) releosed ,nto the otnosphere

ccn block ond reflect solor rodiotion from reoching the Eortht Resuit in brilliont sunrises & sunset.t It will offect ihe ecosystern odverselyL Loweting ol the overoge globol tempetata(e

Fg: O 5'C n sone areas after the /,lt pinatubo eruption

Eg: - 3"C ofter the eruptton of lanbora in 1815 The year fo//owng the hnbora eruption(1816) was caled the "fear without sumner,. Snow fel in New Enonia in ntn

2) Ozone Destruction.L Sulphur porticles con .€moin suspended in ihe ctmosphere for severol yeors{ Reoct ond destroys ozone molecules{ Destroys nitaogen confoining conpounds ihot helps to prevenl ozone

deSlruction

tg: l99l t4t Pnatubo eruptrcn - 10% reduction in ozone tevels around the reoion

75

6) I'ludflows (Lohor\

Tvp|:-L Lohor fndonesion term for mudflow+ A nixture of woter ond volconic debris thqt sweeps down o volcono s slopes+ Velocity of the loho. depends on the slope ond water conlen!{ High viscosity - slow moving - high erosion / destruction{ When moving, o lqhor looks like q moss of wet concrele ihot corries rock

debris ronginq in size from clay to boulders more thon 10 m in diometer.{ Lohors vory in size ond speed Lorge lohors hundreds of rneters wide ond

tens of neteas deep con flow several tens of meters per second, much toofasl for people 10 outrun.

Causes:+ Due 10 excessive roin or melting of snow & glociersd Strotovolcanoes -' effecti\le lahar generators+ Dle to steomy, explosive eruptions, steep slopes ond loyers of eosily eroded

osh thol cover lorge portions of their sides

Effecls:/ Result in hurnon cosuolties os p€ople connol escope in lame{ A lohor's turbulent flow or the boulders ond logs corried by the lohor con

eosily deslroy onything jn its poth-1. Buildings ond volLroble lond moy beconie portiolly or completely buried by

cenent like loyers of rock debrist By deslroying bridges and key roods, lohors con olso trop people in oreos

vulneroble to othea hozordous volcdnic octivlty

Eg 1: Nevado del Ruiz, Colonbia (1985) - Sudden nelrng of sunnit g/acrcB produced olohar wh/ch kil/ed 25,0O0 peop/e in Anero

Eg 2: Llt st Helens, USA (1980)'Lahars transported trees. structural debris and greatvolunes of sedihent. The lahars choked /ocol chonnels and dunped large vo/unes of

Eg 3: /At Pinafubo, Philippines (1991) - In the t'irst few years following the catac\,snic1991 eruption, they have depotted nore than 0.7 cubtc mi/es of debns on the low/andssu.foundlng lhe volcana, burying hundreds of square miles of land._During heavy rains,lahars at Pinatubo can transport ond deposit t'ens of mil/ions of cubic yards of nud in a

. an9/e day Since the 1991 erupfion, lohors fron hnatubo hove dettroyed the hones of morethan to'.ooo peop/e (Ftg 60)

-/6

Tatljc

SEA

d ' JrtdLF+

o 10 KlLOn€iEAG

rype:

Figure 60 Extent of lohors gene.oted by the e.uption of rv\t Pinotsbo in 1991

7) Earthquqkes

Volconic-tectonic eo.fhquokes (short period eorthquokes)produced by stress chonges in solid rock due lo the injecfion or v/ithdrowolof rnogmo

. occur os rock i5 movjng to fill in spoces where rnogmo is no longer present' Hrgh frequency s'qnols. Not on indicqtion thdt the volcdno will be erqptinq but can occur of anytine

Long period eorthquokesVolconic tremors produced by the inJection of mogmo inlo su.rounding.ockResult of pressure chonges during the unsteody tronsport of the mogmoLow-freguency signolsfndicotes thqt o volcono is about to erupfSuccessfally used to predict the 1980 eruptions Mounl 5t Helens & the1991 eruption of Pindtubo

11

Effects:! Couse londslides dnd domoge to property

8).fg4dSlides ond debris avalanches

Type:I Lorge moss movements of aock ond debris from o volccno+ Th€se mixtores of debris move in o wef or dry state, or both.L Common in volconoes with greof height ond where enormous omounts of

moteriql dre aeleosed during eruptaons

Causes:{ Explosive volccnic erupiions-l Collqpse of the volconic cone due to qrovityI Lorge eorthquokes beneqth or neor o volcono..l Intense roinfoll thot sqturotes o volcono with woterI 6enercie deodly lchcrs

Effects:{ Bury river volleys with rock debrisL Creote deep gqshes on o volcono cone or lctrge cralers which in t!l.n leods to

explosive erupfionsL They con dom r.ivers ond lokes cnd couse flooding when lhe tehporory ddms

collopsest Leod to destruction of |ves ond properfy

Eg. A nlEsive londs/tde was generated durng the e.uption of /Ut st Hetens n 19AOPressure was releBed by the renoral of more thon half a cubrc mtle of moterial. whtchtriggered a deyastahng /oleral blast and osh,loden erupfive eruptrcn

9) Floodino

Type:I. Droinoge systems con become blocked by deposition of pyroclosfic flows ond

lovo f lows

+ Volconic erupiions in cold climotes con melt snoM/ qnd glociol ice

Effects:.{ Sr.rch blockcge moy creote q terTtporory dom thot could eventqolly fill wilh

woter dnd foil resultinq in floods downstTeom from the noturol don.

71i

-l The melting of snow ond glociol ices)slem ond possrbly cousrng floods

Jb ku lh laups.

ropidly releosing woter into the droinogeThese floods qre refeared 10 os

Eg: Ihe 1996 eruption beneath the Vatnajokut 'tacier

ln rceland generated s Jokulhlaupthat destroyed power lines and telephone cables

lOl Fanine

l-vpe:{ Volconic qctivities con couse destruction to lorge oreos of fornlond ond kill

livestock in ogriculturol countries. This results in o shorfoge of food_+ Shortoge of food leods to molnutriiion. storvotion ond fomine.t Food oid moy toke sone tine to reoch offecled oreas os roods ond bridges

mcy be destroyed du.ing the eruption

Eg: The Tdnbora etuption of 1815 coused ?Z,OOO casuotties ds o resu/r of farnine ond

Jokulhlaups (Icetdndic tern) occur when heatng of a glacier results in rapd'!4!!try!'!l:!!!!yh"!9!!!9 s/gls!,

I

79

c) ,vlonog,hg Volconic Hozqrds : Prediction, Mitiqotion, Response

.l Volconic hozords con be monoged fh.ough ihe mitigotion meosures to predictvolconic eruptions, control ond minimize the e(lects of ossocioted volconichozords

Predaciion: Pr€dicfron of ihepolentiol hoza.ds dssocidtedopproprrdle m'trqdfi on meosures

1)1to\tt'd drfo(/nrhat bt Ltwt11,1u klkr^12)tl5frr! q{ ljVity3)ohqn%s ln qqr canlotillo Aa)chqnrl: in q rau,.J'aql.,

occsrrence of volconic erupl,ons ond thewith the eruptrons allows for time forto be plonned ond executed.

> /vlitigafion: Miligotion neosures help to minintze effecrs of volconic hozdrds

> Response: Inifidted off€r a volconrc eruption hds occurred, such mecsuresfurther controlond monoge effects of .ssocrdted vol.onrc hazdrds

'I Such meosures hove been implemented with sone degree of success in mqnycoqntries oround the world-

+ In this secfion, we examine the vorious meosures in ploce to monoge volconrchozords. Toke note thot nost of the time, o combinolion of meosures ore tokento monoge volconic hozords. Also poy ottenlion ta the etle.liveness ondlimitotions of eoch nedsure-

Mitigqtion

Monogemenf of Volconic Hdzords

30

ci) Predicting Volconic Err.rptions.l- Prediction methods are being used to prepare ond provide sufficient wornrng

for evocuoiion meqsu.€s 5hould o volcono erqpt+ There a.e two colegories of predictaon methodsi short-term ond long-tem..

> Short - tern pr€diction of volconic eruptions involves monilorinq lhevolcono to determine when moqno is opproochinq the surfoce ondnoniforinq for precursor events thol often signal o forthcomrngeruPf,on.

> Long-tern prediction involves prediciing the nexi eruption bosed onlhe post behovior ond potiern of volconic ocf;vity

{ However, both prediction methods hqve their linitations, given the unprediclobility ond vqriobility of volconic octivity.

Short- Tern Prediction Methods:

.l Such mefhods rely on fhe close nonitoring of volconic oclivity

+ Volcono monitor;ng involves lhe contin(ous collection of one or more doto50urces for the purpose of ossessing o volcono's octivity stofe (precursors)

+ This rncludes monilorinq volcono deformotion, seisnic octivity, volconrcgoses and woter f lows

'I Predicting volconic eruptions using shorl-term prediclion methodi con bequite difficult because some volconoes disDloy pleniif!l precursor {rclivify ondoil to erupt. while others explode violentlv M/ifhout few orecursors

+ Al present, no single precunsor con be used to predtcl occuaotely whenvolcono will erupt

l. Volcqno deformotion

+ Prior to on eruption, mogno will force its woy up the volcono This movrngmogmo will couse cerioin sections of the volcono to be deformed.

+fhere a(e 3 rrays thof volconic deformqlion con be meosured: tilimeters, loSersighfing ond 6P5

11,

a) Tiltrnelers

Tiltmeters ol.e most conmonly used lo meosure the liny changes in the slopeongle or "iili" of the ground o1 o volcdno which indicoles the defornoiion of q

volcqno coused by moving mogrno. ( Fig 6l)

d When mogmo forces the ground up .lhe slope of odlocent oreos will osuollylilt owoy from the center of r-rplift by only o frocfion of o degree

+ Conversely, if the ground subsides os o consegaence of mogmo movingbelow, ihe slope of odjocent o.eos u/ill tilt iou/o.d the .e ter ofsubsidence

+ Tilheters ore highly sensifive ond con neosure ongles equivolent ioO .00006 degrees

Eg: filtneters used by vo/cono observatories such as Coscodes Volcano abservatory.l4efop; Volcano Observa lory

successful exanple!, nlhetets helped volcanologists to predtct eruptlons at r',lt St t/elens in tgBZ

> Ihe repealed r6e of nogna ,nto the done betlore the erupt/ons produced anexceplianol pottern af ground ,/t on the croter tt/oor thot began Z to 4 a,eeksbefore naqna extruded onto the done

> Wifh neasurenenls of dane defornafion. and earthguoke activity, rctenti5ts oflhe USGS Cascades Volcono Observatory tssued eruption warnntqs n the forn ofpredt.tions on Aorch 12, Morch 15 and March 19

> The eruption began with a short-lived expl&tan on Mafch 19 at 7:ZZ p/+1. lavabegan eruptinq on fop of the done during the nighf of March ZO

s?

r\-7?E

TiLI

Precise meqsurements of fhe distonce \etween o loser bose sldtion ond orefleclive t$gel Iorgels ore ploced on the volcono ond obseTvotions ore modefrom the sofefy of fhe volcono observatory.

c 6lobol posirioning system (6p5)A telalively nelx technrque thof {]ses sofellite b.oodcost5 ond triong!lqtion loprecisely loccte the receiv€r s locotron cnd elevotion A series of GpS recetverson o volcono con record very srnoll chonqes in rnflotion qnd lcterol movement

2. Seismic lnoniforing

Erup1rons ore often preceded by srnoil eorthquokesThese eorthquokes ore closely related to mogrno novemenl or pressurechcnges in the rnogmo reJervoir so they provide voluoble clues to possibleeruplion limes dnd locationsPottel.n onolysis of these eorthquokes hos helped revedl the depth ofmogmo reservoirs ond the migrotion of fheir point of origin.

5ource: htf p://volcono und.edulvwdocs/vwlessons/monitol.s.html

b Loser sighting

I'I

How seisnic montfot.ing i5 conducted2:L A netwoak of seismomefe.s dre instolled fo meosure the mognitude (M),

lrequency (F) ond dist.ibltion (posiiion) of eorthquqkes under on o4live

+ A seismomete. is an instrumenl thot meosul.es oaound vibrations coused

I

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by eorthquokes.Fundomentolly, o seismograph i5 o sanple Dendulum When the groundshokes. the base ond frome of fhe inslrument move with it, bat ihertiokeeps the pendulum bob in plcce- It will lhen qppeor to move, relotive 10

the shoking ground As it moves it.ecords the pendulum displocemenls osthey change wilh time, tsfllg4fqgeqtd colled o seismogrom (Fig 62)

To keep lrock of o volcqno s chonging eorthquoke oclivity, iypicolly5etween 4 ond B seismometers ore instolled wilhin obout 20 km of itsvent, with severol locoled on the volcqno it5elf.

This is especiolly imporlonf for detecting eorthquokes smoller ihonmognitudes l or 2

Importqnt sign when volccnic tremors increcse ond move towqrds thesurfoce while the high frequency eorthquokes lessened-

Fig 62: siesmoqraPh

This does not nean thal the method is withouf ifs problems:

+ it is subJect to potentiql inletfetence from other sources of groundvibrolion 5uch os wind ond vehicles

d o poorly chosen sile con sometimes, becouse of the inlerference noledcbove, be olnost useless fo. seismic noniforing.

Eg: As of 2OA2, 27 renote seisntc honitorng st.ltions dre operoting at 9 of the nostactive volcanoes in kanchatka and at A/otd l,/o/cano. on Paronuthif Island n the not themKrile Isldnds

s4

'/ Dala afe ffansnrtted fran lhe stations to three recordng centers inPelropavlo6k kdncho tsky, K/yucht, ond Kozyrevsk.

> Inlernet connectivity among these centers allows Kantchatkon VolcanrcEruption pe.ponse Tean (KVEQT) scientist5 to rapidly ona/yze ddta and issuenottfications of volcanic unresl ol the nonitored volcanoes

Figure 63. Seasmic monilor,ng stotion otbose of Klyuchevskoy Volcono. Russia.

Xlp]]t:p!b5!!st-se!/ t r/2oa2 / f .064 02 /

Th€ composiiion of goses emitted from volconic venfs ond fumdrolesoflen chonges iusl prior to on eruption

I4gtCq-s-g: in the proportions of hydroqen clloride (HCI) ond Sqllgfdroxide (5O2) ore se€n re_lotive to the ploportion of 4/qtgl ySpq!.

Fig 64: Moking soil gos meosurmenfsXlLLt4ty.Sgglaalq-nzlvolcono/monito.inq methods/qds himl

in Volconic 6oses

8i

Eg: Changes tuere noted in the su/phur droxtde ehtssion before the na jor eruption of 14tPnatubo in 15 June 1991 On r''lay 13, its 50, etnBsion wos 5OO tonnes per day. 15 days/ater. tt was 5OOA tunnet per day

4. Chonges in 6rolndwoter Sysfem

{ As mogmo enlers o volcono il noy coqse chonges in the groundwolersystem, cousing the woter toble 10 rise or foll qnd cousing thelemperolLJre of the woler to tn(recse

z Rrse of wcter toble : Build up of goses in volcdno pushes wdter toble up; Fdll of wof€r ioble: Incredse in evoporotion due to heqting by lndgmd

+ By monitoring the depth to the wote. table in wells and the temperotlreof well wotet, spring !!/oter, or funoroles. chonges con be delected lhotmoy signify o chonge in the behovior of the volconic system.

Lohg - tern Prediclion tUethods :

Such methods rely on mothenoticol colculotions ond historicol doto to predict whenthe next eruption is Aport faom predicting when on e.lpiion moy occur, hisforicoldoto is olso useful in ollowing scienfists to predict the fypes of hozords ossociotedwith specific volconoes when o polentiol eruption occurs

t However, this predicfion method ndy only be relioble with an occuracy ofdecodes fo thou5onds of yeor5, depending on the volcono.

'J Theretore, the ofher short:ferm methods ore often mote relioble

Nonetheless, despife their limitotions, long fe.m prediction methods con be verypou\rerful and effeclive in moking cccurole prediciions u/hen conbined togeiherwilh short-te.m predicfion melhods.

5. Recurrence Interval Predictioh

{ By knowing the lost few eruptions of o volccno, lhe next eruption can berolghly predicted using the concept of recurrence lnferval

rJ6

Becurrence interval: The average fine infervalbetween occuffences of a nafuralevenf,such as a flood or earthquake or volcanic erupfion,, of e given or grealef

maanitude

+ In order to cqlculole recuffence infervol , it is necessory to hoveinformqtion on the post frequ€ncy of eruptions.

{ The post frequency of e.uptions con be determined fhrough siudies of ihegeologic hisfory of o volcano.+ Such sludies involve investigoting fhe oge ond chorocleristtcs of deposatsletl behind by vorious types of eruptions. Seglences of rock deposits ond lovc flowsore onnolysed ond'do1ed" ( ie: vio rodiomef.ic dotang). This enobles scientrst5 todetermine the pcst behovior of o volcano{. studies of the geologic history of o volcono ccn ihus help scieniists fo mokeon ossessment of the lypes of hozords posed by the volcono ond lhe lrequency atwhich these types of hozords hcve occurred in the post.

I Once this informotion is qvoiloble, geologists con then mqke forecostsconcerning whol oreos surrounding c volcono would be subject to ihe vorious kindsof cctivity should they occllr an o fufure eruption, ond clso moke forecdsls oboutthe long te.m likelihood or probobility of o volcanic erupfion in the oreo

{ This informotion is then combined with knowledge obout the present surfoceospects of lhe volcono fo moke volconic hozqrds mops which con oid otherscienlists, public officiols, ond the public ot lo.ge to plon fo. evocuotions. rescueond aecovery in ihe event thot short-term prediclion suggesi5 onofher eruption.

Egt Recurrence interwls [R] for eruptions irarease with size of eruptions (as indicatedby volcanic explosive inde< lVEt .

Individuol vo/coaoes - esttnates are based on relatively few events n o conparatively shartperiod of observation. averoge recurrence ntervals and uncertanttes (one stoadardd^ lat,on) at e a< lotlowt ror selerted tolro4oes

. l4auna Loo - since 1832. on eruptrcn has occurred on average every J.B : 3 O yr

. Khuen since 175O, averaged on eruption eyery 3.? ! 6 yr

. Heklo (Iceland) - since 93O AD. a an eruption every 54 ! 36 yr

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. 1,4t. Pelee since 1792. avg 364 ! 473 yr betaeen eruptions (VEI . 3,4)

. f'uJi ' since 781 AD, avg 7l ! 1/3 yr between eruptrcns (lart eruptton wds in t7O7l)

. /Ut. St. Helens'slnce l5OO. a,/g 37 t 58 yr between eruptions, more violent erentsare less freguenl.

h|!p:,//www ruf rrce edu/-leenon,/volcanic hazdrds hrnl

cii) Volconic Hozord l itigotiofl

.l Violently explosive ondesitic or rhyolitic volcqnoes dllow no room for controlor tn,tigotion due fo the ropidity of their eruption ond thei. explosivepowet- Evacuation is the only colrse of ociion ot the firsi sign of newvolconic ocfivity

{ In the ccseof non explosive bosoliic volconoes, evocuoiion is olso essenlidlbut volconic hczords con be mitiqoled throuqh physical confrol meosuresto sone exfeni to reduce the domqge to property

1.Early l1/arning Systen and Evacualion /l'leasu.es

+ For those living in o densely populofed drea neor o volcono. evocuqlion i5 the only

9fi99Iy9_5ot9lj 3tlj9! Once indicotions from p.ediction nefhods ore receivedthot o volcono ii about to erupt, evocuction of people con be comied oLlt by theouthorities 1o minimize loss of lives

4llowever, fhe time frome will be shori os forecosts are b<rsed on weeks or evendoys ond on evocuqtion plon must be olreody puf inlo ploce in order to corry it oufsuccessfully

+ Dofo olso hcs to be relioble in order to woracnt evocuotion os seismic lremorsmoy olso be produced by other tecionic moiions

+If evocudiion ts rJeloyed, exit routes moy be blocked by lovo flows. pyroclosticdebris ond mudflows

+Ihus, effecli're lines of cornmLrnicotion ond eorly wo.ning system ore highlyimporiont-

{ Public educqtion is olso necessory to increose conmunity preporedness for

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{ Evocuotion drills con olso be conducfed to increose community preporedness.

Eg fn Sokuta'Jtna, Japan, an annuol evocuattan exercise is put' n ploce on 12,1, Jonuary(anni,/ersary af the 1914 eruption)

Exanp/e of warntng systen used in the IJS:

evqcuotion ond increose conmunily oworeness oboul pofenfiol volconac hozords.

UsGs Code af Alerts for Washingfon and oregon (Cascades Bange):. Notice af Volcano Unrest: Levet One (Coutd be... ). Volcono Adwsory A/ert: Level nao (Most likely ). Vo/cano A/ert A/et-t: Level Three (Definitetr,')

USGS Co/our code for A/aska:. Creen: Vo/cono is n its nomal ,'dorhant,, state (normal setsmtcity and

funafolic activit)r ts occufrinq). Ye//ow: Volcano is restless. Setsntc activity is elevated potenhol for

eruptive activity ts inct.eased A p/une of gas and :;tedn nay rise sevefd/thousand feet above the vo/cano which noy contain ninor aaounts of ash. Orange: SnaI ath eruption expecfed or confirned. ptune(s) not likelr torise above 25,O0O feet obove sea tevel Setsnic dtiturbonce recorded onloca/ seisntc stations, but not recorded at nore distant /ocotton,

. ped: Large oth eruptions expected or conftfted. ptune likety to tiseabove 25,OOO feer above sea levet Strong seisrrrtc srgno/ recorded on o//loca/ and cohthon/y on nore dtttoit stdt/ons

2,Hozard Aapping

{

+

{ Comtnonly ased mefhodond to identify oreqshozords when o volcono

io indicote the fypes of expected volconic hozordsthot ore ai different degrees of risk io these

el.upts.

Hozord qqled bosed on pdst erLlDfion doto ond informotionr]ozq|o mops ore consrl"ucleo oosed on odst efLlDtton doto ond informotionfrom the qeoloqic moppinq of volconic deposits oround fhe dl.eq of o volcono_

mops constructed bosed on odst erLlDfion doto ond informotion

Such hozords mops delineote lones of donqer expected from the hozordsdiscussed: lqvo flows, pyroclostic flows, tephro folls, mudflows etc

There con 6e different zones depending on ihe impoct creqted by the postvolconic eruptions in thot qreq.

Hozcrd rnops ore r.rseful for londqse plonninq ond the olonninq of

'1

evocuotionroules of locol communiiies.

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ffi igSC NLiee Ard.rrltes n Fc,rbir,Jden Zone

\ R,ve.s ffi Frrst llan er Zooe

- Roads i ialer-c,r:d {l6r}de! /.'r} e

F,g{lfe 65. Hozord mdp of l t i'rleropi bosed on the 1969 eruption

Hazard naps have been used effectively and successful ih a nany cases to assist inevacuation Sone exanplet:

> Soufriere Hi//s, lUontseftat (Caribbeai): Priot to lhe 1997 eruption, scienflstspredtcled pyroc/astic flows and ash falls due fo the eruption. Thus, thousands ofpeople uere evdcuated fron nearby oreas around the

'/olcano These dreos were

dec/ared as exclusion zones" Ai o result of these excluston zones thoucands oflives were soved

> /'lt Pinatubo: While evalualing the thrcat from the volcdno u 1991, thete scientBtsdiscovered that lhe gentle slopes surrounding Pinatubo had largely been created b).counfless gidnt nudflows of volcanic debns (lahars) froh the powerful ancienteruptions thdt buih lhe volcano. Hence, hazord nopping narked out potential areasthal would be affected by lohars rhis helped save lives in the 199/ efuption

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This does hot mean that the method is withouf ifs ptoblems:

.L Given the unpredictobilily of volconic qctivily togethe. wifh unforseennolurol evenis, there hove been instonces where hozords mops hove beenin-occurofe.

E9: Whi/e the 1980 Mt' St Helens efuption wos accufate/y predtcted by scientists, thehozard map conslrucled foiled to take inro account the laterol blost whrch occuffedunexpected/y later on. As a result of this, o nuaber a/ peop/e wtthin the "lateral b/ast zone,'uere not evacuated, resulting in o s/ightly higher,than-expected death toll

3.Physical Confrol tUeasufes

a) Lava Divelsion by Lava Flow Dans and Explosivet

.l- Built to divert fhe flow of lovo io protect towns ond give more tift\e forevocsotion

I The design of the dom must be oble to resist two forces:- The mds. pressu.e of the ldvo ogdrnst fhe borrrer, whrch rncreoses with

flow thickness; The momenium of the odvoncing lovo flow which increoses wjih the

velociiy of ihe ftow.

I They ore most effecttvewhen constructed properly

I However, the doms built ore often improvised hostily os oulhorities rorelyknow where ond when on eruption will occur., leoving too liltle time to constTucto wel! engineered diversion woll

+ In most situqtrons, they ore conslructed quickly offer on eruption stdrtsond fhe likely poths of lovo flows ore known Thus, they ore usuolly mode ofovoiloble rocks thot con be stocked guickly.

I Another technique is to qse explosives to breoch the solidified woll of thelovo cnd drverf its flow.

b) Coolng Lavo Fronts with Water't Used 1i] stop or slow down on opproochinq lovo front

t- Roprd cooling creofes o'slone woll' to slow the flow cnd moy divert ihe lova

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flow loterolly+ success depends on lhe obility to deliver obundoni volumes of cooling woier

fo ihe lovo froni

Eg: Both nethods were used effecttvely during the eruption of Mt Etna in Italy in IgBj toprotecf l4onte l/efore and Sapienza against nosnve laya flows

; Fxplostves were used to duert flot! fron Sapienza. Although dtversion was nintnal,the cool debr6 blown fron the explosrcn credfed blockagd in the lova flowdouns lreont. s/oi/ing i ts p rogress.

> More thon IOO workers 6ed bulldozers and trucks to build o massrve dtversron wa//upitrean of ,Uonte Vetore ta divert flows thot threatened o lot-ge hotel and ands lronon i co / observa t oty.

> fhk bdrrier was overtopped ond another one u/os built I0Oh1 to the west mesecond dan effecttuely divert'ed the flow

> A dan 14n high successful/y b/ocked the lava flow and diverted tt around cflticalfoci/ities in Soptenza.

> A/though the don construchon cost was g3 mi//ton, /osses wou/d have been onestmated $5 to $25 nt/ltan tF thev were not buitt

Another Exontp/e> Dunng the 1973 eruptions on rhe Blond of tleinaey n fceland, the connuntres and

o fisht g hotbor ut6 thredtened, The Ice/anJtc sohttta u/as lo punp endless tons of seawater fron the Atlantic

O.eaa onto the /ovo. tltis nethod app.ari ta have wark we/l although sone scientitts felt thot the

eroptuon ond flows !,/ere c.orng ds the seawater wos opplied

ciii)Responses to fhe ef{ects of Volconic Hozords

.! Ernergency relief as importqnl when locol conmunities hove been evocuotedor Tescued frorn oreos offected by volconic erupiions

{ Emergency personnel must be ovoiloble ond well,prepored.L Ernergency .elief comp.ises the provision ol shelter, food, bosic hygiene

omenities ond medicql core{ In less developed countr,es, internotionol oid is offen required os locol

resources mcy be overwhelmed

Eg: Aid agencrct (such as Untcef, UN wor/d food progranne.) rushed in to help peopledisp/aced by the eruptiotr of r'"4ount Nyiragongo, 2OO2. near the town of 6oma n theeastern port of the Denocrotrc Bepublic of Congo A river of red hot tova flow cut throughthe town, destrolnrg property ond contaninotory water supphes Aid agencies he/p provtdetenporary shelters dnd faod for thousands of dsploced people.

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| "a" L"uet Questions: Volconic Hozords ond responses

i) Differentiote the types of volconic octivify ossociotedwith the different plote boundoriqs.

r------------------1;;-------------------lNoieIt rs necessory To emphasise thdt drvergent boundqries ( and hot spot oreos) dredssociofed with bosoltic mogmd ond g€ntle eruptrons, while convergenr boundories al"e Iossocrdted wiih ondesrtic/ .hyolirc mdgmo dnd exptosive eruption; IL--------- ___________t

/Uusf include: (Secfioh 3q)) Eosoltic, ondesitic, rhyolitic rnogmo

) Volconic explosivity index

ii) Discuss fhe effects of volconic erupfions.

/Uust include: (Section 3b)) Hozord

) Eorihguokes, tsunomis, mud flows (Lohors), londslides, otmospherrceffects, flooding. fomine, heqlth problems , lovo flows, tephro , pyroclosticf lows. volconic goses

iai) With r f erencz to cose studies ossess ottemDfsmonoge volconic hczords.

I

When ossessrng monogelnent strotegres. it rs necessory to:) Address exomples $/here the strotegtes have proven to be successfui ( or NOflnsuccessful) in mdnogrng the impocts of eo.thqudkes.-> It i5 dlso necessory to exploan why these strotegies hsve been successfui ( or

L.r,3.:":.!ll____

/Uust includes: ( Section 3c ond 3d)> Prediction, mitigotion ond response) Evoluotion of prediction, mitigotion ond response sirafegies

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