\ ...:;;.-,

022395

by

:1ecoras ITo. 1. 57/L~3

SUG ~4.RY • e •••••••••••••••••• 0' ••• 0 ,' ••••••" •••'-'

INTRODUCTION ............ ,".......•...... ~ ... 1

STRUCTURE OF ACTIVE CR~~TER .AFD~;FVIROlT:;::::HT

TO 30UTH-E.:~S'I' ••• I1-.................... ~

l1.CTIVITY ••••• 0 •• ~ ••••••••••• 0 0 .0' iJ. o. .. • • • • • 3

1. The explosive nature of activity.... 5

2,. Lava flows "'-'-~""""'O""""-""'" 7

3. Other pheno.mcl1.::i ••••••••••••••••••• -.. 8

1. Til t tile t erre c. aings •••••••••••• 0 •• 0 • • 9

2 1 ' ;3hock reco:d]er •••••••••••••••••••••• 9

3. obse:i:'"fed . " .." . 9

COl~CLLJ3 IOl-;3 ••••••••• , ••••• 0 • 0 • 0 •• .; • • • • • • • • • 9

11~}:S~{J}i'''CZ •••••• ~ •••• 0: ••••• 0 " • • • • • • • • • • 10

FIGURD 1

Aerial view of Manam Volcano from south-south-east.

January 14th 1957,

,

1

Man~m Volcano became active 0n 8th December 1956 9

but ~as not reported until 5th January 1957. The activitywas investigated from 14th January until 5th Februarv whenit was concluded that if the pattern of activity sho~~d nomarked change 9 there was no danger to inhabitants or theirgardens.

The active crater is south-east of the top of Lanam swhich is in the fOrtil of a tri1'L1.I'cate ridge. Lain features 01'the eruptions were DS i'ollo\JG,

i.' ~xjlosive activity predoGi~ated.

2. j:ost i':;''''3~ment;,;; 02' reJ-hot lav:: ejected were angular 9

ond 3CC Ul'.lLl1a telJ on the riLl 01' ti1e cra ter ~ thevc'lectu811t r!loveJ cJO;,iD '~ill:; slopes' ",.s3vaL3ncl1es" whichreser,lbleu ty~')ic.:~l il,.. 2. il Ivra flows (the -I ~:L!.6-47 "floViiS Il

probably occ~~reJ in this m~nneI').

3. Subsidiary flows 0:':' ·vj.scous CJ12Gma occL1.rred neal" therim of t~e crater.

4. 11: ino l' BC '~ivi ty :cese,:lbl i ng steam explos ions occu:;,"red1'rorl1 sources, in the deep valley south of the crater.

5. Dust and cas from eruptions was negligible; therewas a strong glow from the crater p sometimes visiblein the day.

No significant earth movements we:,,"erecorded by thetiltmeter or sho~k recorder that were set up.

The first report that Manam Volcano was active wasreceived by signal from Bo~io on 5th January, 1957; the glowfrom the crater had been seen ct nicht from BOGia durinG the vre­ceding week. On the ~ight of 10th January a lava flow from thecra ter was also wi tnesseJ fro:.i the l,e\i Guinea n1[; inland ncarBogia~ and SOlliC detoi1.::.tioD8 viere hearu', ;1'h1s ini'ornlation wasalso sent by SiSDOl os well ~8 cJetcils of an inspection from thevvor~,:boat "L8~·.:anaill Oil 11 th ':;cnuDr~, Thc District Conmlissioncrond DistJ:ict Oi':i.'ic13r of ;.: (jan.:; lJistrict COt1GLlcted an :o:erialii'Js;,)cc't.io;-J ai..' Lanai;] on 11 til~ DL1'l; S •• Vi very littlc becaLlse the upper2,000 l'cet 01' the cone \I;'::S cCJ~)ed L~, cloud.

The wri-cc:L' i..~o:JarteC l'rO!',l Rabaul on 12th January anGinspected Lanal,l l'l'O\d the c:ir en route l':adang. On this occasion,also, the sLlmmi t aDd c:;,"a'I.;Ol' we:.."c cappcd by cloud. i~nothcr aerialinspection was cOiJducteC::~ in vain~ when travelling to i.war Planta­tion on 14th (sec ::.:'i2;'-1rc 1.) T11c first two nights on LanamIsland werc spent at Tabelc Village on the south coast. On 16thJariuary~ the writer moved to ~aris village~ farther east alongthc coast, where better observations of the activity could be madeBam Island was visited on 20th to rcview conditions there and toobtain a tiltmeter and shoc~ recorder for further observations onManam~ These instruments ~ere installed ncar ~aris on 26th Januar~and readinGS and records were obtained until L~th :Lllebrul:.~ry. Inves­tigations were completed on 5th February.

FIGUR~ 2

Manam Volcano from south-east. Deposil; s 0:' recent

activitY$ as at Janu2ry 15th, shovVTl in er>osion

channel in upper> par>ts of 1946-47 flow. No de~osits

had formed on the steep slopes of "Ghe semi-cone at

tha t tirae. The obs erv::J. "Gion po in t of Januar>y 31s t

February 1st is also shovm.

2.

I 'v,as assistcQ uLlrins .l~his period by cadet PetrolOfficer ~. roc~en? anO his hc10 ,.nC thst Biven by ~ssistant

District Or:t'iccr ·.'1.J·o~1nstoil of' BOCie is ':':c:i~no\'ilcdGccJ. Theco-o.:,e:;."otion 01' t~le Dist:."ic·c CO'ji!"lssioncr and Distric·c Officcr~

L3dan[;~ vias also -:,:pi.)rcciatcd~ '::ild than,;:s C:::i."C GL1C to l:'sthcrsBochrd and ;,erni of tlle Ro~,]c,l1 Catbolic Lissioil at BienS; for inform­ation and hospitality. N~tive people of ~aris Village seemed tohave a bc·~ter knol''iL.:dge 01' 'vIG~S of access to the upper parts ofthe 1946-47 lava flow and v8nt~Be points than those of otherVillages fart~er south. .

STRUCTURE or .:··.CTIT.~ Cl~_';TER AND ENVIRONVIENT----,-_ .. -.-....__ ....... __..._-_._.~ ..... ' ..._.......'._---_ ...~-------------

Best (1953) discovered that the crest of iianC:Hil consisted"ot; a tr~furcate O'idge, the three axes 01:' 'iiil1ich are ol"i:;i·jteCi at70 , 195 and 313 (magnetic) respectively." A l.:r[;e t1fU!ilOrolelfwas sittinted not far below the crest to the north-cast; the volumeof vapour from here showed no apparent change between November1954, when Manam was visited by the writer, and January 1957 whenthis investigation commenced.

The active crater~ which showed signs of eruption in1953, was south-cast of an~ below the crest. It is situated atthe summit of a semi-cone M built out from the steep western wallof a broad avalanche valley which extends towards the south-easternC08st~ The inner walls of the valley are mostly vertical Gnd com­posed of fragmental Muterial interwoven with numerous small lavasills ond some dy,;:c~ (sec ~:'ic.4j. '.rIle outer sloDes enclosin~ thevalle~l eire i'c:.:'irl~r stec~):i1cJ ucc~:Jl~' l-:Lssccted 1)~i streom beds. Theyrepresent tl12 outc;I' su:c:L:'acc oi.' t;le old caldera wall referred to byBest. ~n ojscrvation point useJ on 31st January cnd 1st February:1:~5I:"v8s 3bovc the nO~'G~lCrn \islls o:i:' tIle avalanche volley; measure­ments [,lade \iith an all",roid lJoI'Oj.:;tC11 showed that the sU[jlmit of thecalderc wall ;lere ',,'os c..:bout LI·~O(jU i'cct :::bovc se8 level. -vegetationvaries from dense rain-forest on the lower slopes to mainly brackenand fern trees :i:'rolil .3boL1.t 3 s 000 feet to 3,400 feet obove sea level.Small brscken :nd sedge-li~e )lants were distributed sparsely over~

~ppat'600 fe ot. The L1pp,'::C )C.11 ts of the cald er'::l be tr,ee n the avalanchevclley and the nc~t l~rcc steep-sided valley south to south-·west ofthe cr2 to r differ frou ·GI1C 8bove in tha t they are covered with dens erain forcst to the summit (sbout 4,200 feet above sea level).

The semi-cone below th~ active crater occupies the greaterpart of the floor of tho avalanche valley. It is separateCi from theinner walls on the south by a narrow deeply dissected vclley, and erthe northern side by a brooder valley which narrows in the upperparts towards the Ijjestern end. The relati...:,n is s;lo',vn in l"igU11 C 2.The structure of the semi-cone Cl,t the western end is not l{no\Jn.Figure 2 olso shows the lova daposi ts from ;Jct iv i ty in 1S'46-47. The:·8ppear to have accumulated mostly on the northern side of the crateland flowed in an erosion channel around the northern margin of thesemi-cone. At the eastern base of the cone they linked v~th depositsfrom the south side Gnd spread out over gradual slopes to the coast.The gradient from the eastern base of the semi-cone to the activecroter in the northern channel is much steeper. The 1946-47 lavadeposits in the photograph arc dark compared with the small narrowribbon of recent material, shown light crey, os at 15th JanU\3r~T:

1957. The recent lava occupi~s an erosion channel uithin the 1946-~­flows. Subse~uently this channel became filled Dnd the 12va becanto 8ccumulate in other ch8n~el3 u~til by 2Gth January most of the1946-47 deposits had !Joen covcr'c6 Ciovm to the b3se oi' tile semi-cone.The recent deposits? howc7cr s h~G not proceeded below this lcvol,about 2~500 l'cet above SC':'i l(;vi~l, bci'o:....'c obsl:;rvations we~:'o completedon 5th ~ebruary•

.v. ~h~·~·~·S ~"f;;-J~'~E' ·~·~~·61~,~·~.;·;.,·llfI~~~~·~L;J·;;·{:·~{~·t~i~ir~~·c·6~·cscnTsTl-i·\=· ·h·~~Il'-oY··_--_·

The steep eastern slopes of the semi-cone ~ere coveredby small light-coloured scoria fragments ~hen photographed on15th and 17th January (Fisures 2 and 3); these were apparentlyc) eposi ted during tl:le last eru)tion in 1947. Some stil211 "islands"of older leva flows and deposits protruded through this cover. Agrey veneer of recent lava ~ragmonts had covered the scoriadeposi ts by tho time photographs were t3kcn from the o~Jservation

po in t to the north (se e Figura 4 9 31,11 157 ; ~i[;lUl(; 5 S 1/2/57). .

Thermal activitY9 other than th~t from the second crcterto the north 9 was observed from small vents in stoep-siGed ridgesextending from the crest of the volcano towards the cctivo crater.

The notivG people o:r ',/eris Village first noticed tho"Gactivit~T at the crater ilad clEnscd l'rorll the usual emission ol'white vapour clouds to ,_;n c:plosi".,rc phuse on Btl1 Deccl:lb81"9 '1956.A stUdent who lwd rctuI'ncd ;lOLj(; i'l'Oi" .·.L:;~~is;lz...i'cn on holidc'ys wasi\:;irly ceI'toin of this dote. :.:11C initiDl eJ:plosivc :".ctivity ,wsnot hcnr':J 9 but ,jas suC:...;,;s;;,:;u b~T -ell,; 3l!C1St"liodically ejectod lcvc.1i'rozrllents reser:lb1inc blcclc ;.Ju:i:':t's ai' sr.Jo~:e.

"./':;:""i8 vilL:·.~e is <:1Jc,ut 2 ,,;iles C,::S"~ of' the crotcr andoffers the Des'c ViOVi of 'ello 2ctivit~-. Sound effects ()re also/valle,rheard clearly because t~c :vcl~nche/B211s arc open tow()rds the ~

coast just SOllth ol' llc;,~e. Observation from ".loris between themonths of November z:nC 1.:"::""C11 bc:~s the added sdv8ntae':; that ·thewind (Juring this ~'c1"iod is :':(;l1c1"[;11:>T from the north-west~ andsounds ere hoard better th2n ot other times of the year. A dis­odvantasc of m::king oTJsor-{c.tions during the "north-wcst"- seDson 9however 9 is that there is \!lOl"O rain, Dnd cloud caps cover thesummi t areo 01' I.IonNil, porticulcrly on the south-enst side, formost of the time.

Li ttlc is known on Ii2nom IslDnd of Dctivi ty between 8thDecember, Yihen explosive cctivity '.iGS only r,lild~ .:ncJ Christl'.los.This is due t~ the foct that most of the people conGrecat~d at theEiong Mission on the north-Hest coc,st .:::no thct clouu covcj1 ed thosummit during that period. The Joris people returned to thoirvillo.ge at Christmas and observed very strong explosive octivity.Fine dust from this activity settled over most of the south-eostport of the island. EXplosive octivity continued from then untilat lcost the first week in FebruorY91957. warls people statedthst it wDS most intense in late December, 1956. They scorned Quiteunperturbed by tho noise of ,~etonotions ond the fact that theywere probably nearest t0 9 and bec8use of the physiogr2phY9 morelikely to be affected by tho activity tlan othor people.

Other geD.::rol il1:i:'orL,c.ltlO .. on the c;ctivity, su)plic(, byI'ether .".crni of the rl1issiolJ station 5 oLi:'icCl'S 01' the ::)eQ2rtment ofra tive' .:':I:'i'a irs [:nu i'l"O!J i'J~T O\ill 01')6 cr",,;::.', tio ns 5 is 1 is tell in chro nol­o[;ic:::l order 11C:'OLmdcr.

19~6:--~-- - c·Dccember 9 2(9 20

(,-,\ :i:'rot"11 Bicne 1:i ss ion b~'r dar:~ colouredc.j v

C10lld :~ 1"01"11 cro"Ger( lJ) f1"om BOGic, by glow' at nigh t.

FIGURI:i 3

Manam Island peo:'llc; 0~1 the northern rim of the

erosion channel in 1946-47 deposits jus t aoove the

end of recent deposits~ ns 2t January 17th 1957;

the north-eastern slopes of the semi-cone are shown

at upper left l'ising from behind south benl\: of

eros ion channel.

.~.9.2l;,.Jai1.Uary 1 - 9

January 10

January 11

Janu8.ry 12

January 13

January 14

January 15, 16

Jai1.Ua ry 17

4.

Glow from crater seen from Bieng andBogia at niGht. Occasional dust cloudsseen durinG day from Bieng.

From midnight on 9th, stronger glow thanbefore Gee~1. above cre.ter f:i.~orJl Diei1.g, z:i1.dalso heavy dust cloud during day.

Bogia re:90rted lava flows, and th8.·~ deton­ations were heard between 1900 and 2115 hours.

Inspection by Assistant Dist~1ot OfficerW. Johnston on 1[{orkbo2.t llLakal1.ai;l. Hereported that there were detona tions everyfeg seconds; that there was 2. lava flow,about 20 y2.rds wide, which extended for one­third of ·che way dovln from cra tel", 8.nd th2. tit was "s till trick], inG"il ; nls 0 th2. t onlyone ven"c \"/8.S erupti:ng.

Prom Father Aerni, Dieng Eission - red gloVv'seen 0245 hours and detoil~tions heard bylocal 11.2 tive peo:qle tha t night.

Glow from cratei-' at night seen at Bieng.

Detonations heard at Bieng, Tabele.

Frequent detonatioi1S and strong GloW" fromcra tei" at nights; glows were sometimes seenat t.imes of strong detone. tions during theday on 16th.

Bas e of the reCei1."t lava II flowil vis i ted. Thephotograph, Figure 3, was taken at this time;the following observations were made -

(1) lowest deposits were ~bout 2,500 feetabove sea-level;.

(2) they were s~ill hot:(a) a 0-200 C. maxiJnum recording

thermometer ~as inserted toabout 6 incges; mercury roseto over 200 C. in 7 minutes,and therrnometer githdrawn;

(b) a sapling stick inserted about afoot iilto 'che de~;:>osi ts had charred2.ndw8.S gloV/ing by the time it waswithdrawn about i hour later)

(c) heat haze was strong above thedepos i ts;

(3) macro-examination of rock types showedthat new deposits composed of porphyriticolivine basal t aild apJ?eared very similarto the basalts of the 1946-47 lava flow;

(4) new deposits were mostly scoriaceousand grey in colour; the only differencefrom 1946-47 material vias the outsidecolouring, ffi1.ich had become red brovVl1.by deuteric 0.1 tera tions ai1.d \fea thering;

(5) gas was not obvious; it vas interestingto note that birds and insects existedin this area (also, later, that parrotswere nesting in the upper parts of thevalley walls within a mile of tne crater);

(6) lack of vegetation in 1946-47 deposits iscons idered to be due to their un"cons olida teeand unstable nature.

5.

At 1400 hours while returning to thecoast~ I heard 8. loud noisc f~om thecrater area. The noise, which frightenednative gUides~ was probably caused by an

. aV8.1anche of lava fragme:i1ts buil t up atthe side of the crater.

~h2t appeared to be actual lavs flowswere witnessed that night; this isdiscussed in more detail later.

January 18 - 20

January 22

January 22 ­February 5

January 31 ­February ·1

Activity was the same 8.S during the period15th-17th January.

Vihile returning from Bam Island to Bogia Isavl' a second s tr'ce:tm of newel" fragmen to.rydeposi ts in ano·eher erosion channcl northof the first described. Tho sumrlli twasobscured by cloud. A thin stream of vapourwas seen rising from the avalanche valleysouth of ·ehe cr::.,- tel'; this phenomenon wasalso observed by Mr. Johnston during hisprevious inspection of Manam. It was at­tributed to either thermal activity or dust8.nd steam ris ing fro!·,l the rare bombs whichfell in this valley. Subsequen t inspectionof -chis v8.11e~T both from -che coas t e.nd fromon top of the enclosing walls failed toreveal either thermal activity or any recentbombs. It is possible that the latter haddisintegrated and were not imnediatelyobvious amongst the scree deposits in theupper slopes.

The nature of activity vvas unchanged; therevlere frequent detons. tions mas t of the tiDe andoccas iono.l lava flov/s Here s eell by ni@1. t.

The closest inspection of crater 8.c~ivity

was made from an observation point near thesunID1it of the caldera TIall on the north sideof the avalanche valley in Which the activecone viaS s i tU2c ted. The pos it ion is shown il1Figure 2. It afforded an excellent view ofthe activity at times when it was not coveredwith cloud. ~he photographs (Ficures 4-6)were taken from the observation point.

Gore detailed descriptions of the activity and otherphenomena associated TIith it are Given ~erelli1der:

Observetions made during the investigation of activityin January~ February 1957 su0gested that the lava Ilflows ll ofthe 1946-L~7 activity were not true ;'aa ll flows as suggested byBes t (1953). They were similar in their s i tUE!. tion and com-posi tion to ·che deposi ts of the recell t eruption~ vvhich wereapparently formed in the follOWing manncr:

(a) Lava in the red hot condition was ejected by thefrequent explosions on to the outer rim of the crater;a slight inclin2 tion of the inner 'l"Jalls of ·ehe cr2. tel'or of the conduit is suggested to account for the factth8.t little material fell on to the eastern flanl<:s ofthe cone.

FIGUR~ 4

Crater activity at 1830 hours? Jsmuo.ry 31st 1957;

slopes of semi-cone alrnost covered by new lava

fragrnen ts. Vapour s treaDs from lava bO[r}bs rolling

dovm slopes are shown (left of cent re) D.nd c.~lso

slog-moving avalanche (riCht of centre). In bottom

right h2.nd corner, 0. SpUl' COnl};:Josed of i~"lterbed.ded.

fragmentc.ry mc.tGl"ia1 and c;mall sills is shovm.

Photo from observation point.

ro.

(b) The pyroclastic materi21 was composed mostly ofirregularly shaped fragments of lava, some quite18.rge; there was very 1 i ttle dus t. '1.'11e maximumheight to which it was ejected appeared to be nomore than 1,000 feet above the crater; most ofthe ejecta· therefore fell very close to the crateron its outer slopes.

(c) When conditions for observ2tion were good ordetonations could be clearly he2rd, fre~uency ofexplosions was calCUlated; on the average, sixor seven explosions occurred per minute. Thismeant that accumulstion of pyroclastic materialwas rapid.

(d) Material heaped quickly in this manner wouldform an uns table mass; angulari ty of the fragm::mts,however, would enable th~ mass to become quite largebefore the force of gravity and frequent jolting fromexplosions caused it to collapse and slide down theouter slopes of the crater. These slides, oravalanches, which were slow moving (estimated speedabout 1 mile PCI' hour) had the characteristics of"aa;; flows and could eas ily be mis t<;>.ken for them.

(e) As the lava fragments slid dO\in the slopes theyoccupied the lowes t topographic fea tures, such asthe erosion channel in which the first series ofII flows 11 was witness ed s and beCCljjle spread out alongthem. Subsequent avalanches were superimposed uponthese and another accllinul~tion of material simil&rto that occurring near· the rim of the crEeter, com­menced farther down the outer slopes. A furtherslide of this mass of material commenced, ther'efore,whon it became unstable.

(f) This process was repeated until eventually hugemasses of lava fragments were involved in th~ slidingmovements. Such an avala~l.chc; occurred yrhen thG \/ri tGrarrived at the obs0rvation point on 31st January. Asthe Whole of the SUIl1fjli t area was shrouded in cloud,the noise of the movement was not imruedi2tely recoz­nised; it sounded like a heavy shower of rainapproaching. A photogriph (Figure 4) taken latertha t day sho'1'13 an avalanche wi th thin vapour streamsblo¥ffi to the south by the prevailing Wind.

(g) If activity in 1946-47 was the same as thatdescribed above, the repetition of accumulationof pyroclastic deposits followed by avalanchescontinued until after the masses of fl;2.gmentarymaterial flowed into the sea. Explosive activity,therefore, and not lava extrusion would have beenrespo~lsible for the extens ive \I flows;l.

other features of explosi~e activity were as follows:

(1) Irregularity of shape and angularity of lavafragments ejected during explosions, referred toabove,w8.s noticed mainly during observations atnight. The rna terial examined during ·~he groundinspection on 17th January was mostly scoriaceousand only poorly rounded by sliding; there was noevidence of lava fragments having been fluid whenejected. High viscosity is therefore suggestedfor the lava in the conduit. .

FIGURE 5Deposits on slopes of semi-cone, as at 0800 hours.FebFQary 1st. Base of viscous lava flow just leftof and below white vapour in centre of' photograph.

Photo from observation pOLut (using 90 mm. lens).

FIGURE 6Minor activity in steep-sided gully below southern

slopes of' semi-cone•.

(~at 1745 hours, January 31st 1957;

(b) at 1745 plus about 30 seconds.

7.

(2) Some fragments (or bombs) fell beyond the ZOl1.eof accumu18, tion near the cr8. tel" rjjj1 and occas ionallyon the easterl1. side of the semi-cone. Some bombsalso apparently fell into the avalanche valleyssou th 211.d VIes t of the s umt!1i t of ManclD1. ihe 12l"gel"of these wi thgl'ea te;' momenturH travelled at Z1"e2 tspeed (estimated up to 40 miles per haul") down thesteep slopes; '~hey came to rest in flatter oreroded areas Where furthel' progress was im:r:Jeded byscree or large boulders. Bombs bouncing dov.n theeas tern s lopes of '~he semi-cone a t night produceda spectacular effec'G. As they bounced, scores ofred hot fragments flaked or broke from their surf.J.ce,producing a shower of sparks; the noise, sometimesclearly audible from the coast, resembled that of alocomotive engine gathering speed. Lines of sma.llpuffs of vapour from this type of activity are shovmin Figures' 4 and 6a.

(3) Voluminous clouds of dust and vapour such as witnessedduring explosive activity at other volcanoes in theTerritory of New Guinea since 1953 were markedlyabsent during the Manam eruption. 17'ine dust, however,did at times settle over the south-east part of theisland.

(L~) Based on the sound effects, explos ions a t the cra tel"would be bet'~er des cribed as deton", tions. At timesthere were loud sharp cracks as of thunder iL1mediatelyoverhead.

(5) At night when visibility was good, Q continuousgloW' was seen from the cl'ater. The colour andin tens i ty val'ied from dull red when quies cen t tobrigh t orange red El t times of explos ions. The glow,occasionally also seen by day, sug~ests that thetop of the magma was not fe,r below the rij',l of thecrater; thermodynamic energy was apparently insuf­ficient to force the viscous lava higheo_' in thecondui t aild gas aCcuIn.ula tiol1.s caus ed the frequen texplosions. Jet,s of i1flame ll sometimes 8.CColJ1::?aniedthe explosions; the jets could have been due toeither gas or showers Of incandescent dust. 'rhecrater glow can be seen in Figure 6b, and a jet offlame, in front of the black explosion cloud, inFigure 4.

R.._-_ J:J~a,.Y..§l__.EJ.9!V1i -

The deposit~ formed from Rctivity in January,February 1957 were composed mostly of ejecta from the crater.Some lava was contributed by what appeared to be sm211 lavaflows from the rim down the eastern and south-eastern slopeSof the semi-cone. The exact nature of the activity could notbe determined during the inves tigc, tion. Ac tual flows werespasmodic and best seen by night; they were often obscuredby small streams of vapour emi tted at the same time. PeaturesWhich were obvious were as follows:

(1) The lava was extruded from vents and fissuresin a small ridge on the eastern side of the semi­cone; it appeared on most occasions to be squeezedout as large blobs by internal pressure, and rolleddown the slopes in the saii1e manner as describedpreviously for bombs falling on this side of thecra tel".

8.

(2) 'Thc ridge extc11ded from the, rim of '~he cpa tel'"to about ]00 feet belcw; it may have been aviscous lava flow whose surf2ce had cooled andsolidified (sce Figure 5). Main sources ofemission were just below the crater rim, in awide band nec.r the bot'com and from points inthe periphery.

(3) Flows, continuous for short periods, wereobserved on the nights of 17th Janu2.ry and1st Febru::.ry. Thcy originated from the ventor fissure just below the rim and apparentlytrcvelled small distances over a shallow zonebefore the slopes became steep; hel~e the )Ee vabroke off and rolled a~ay. Thc flows left ared trail in their wake.

(4) During observation on the morning of February1st, two other solidified lava flows werenoticed south-east of the/described above; they loneextended only a short dis t2.nce from 'ehe l'im ofthe crater.

(5) Fragments of lava from effusive and explosiveac 'i:.ivi ty eventually covered the 1 ight-coloul"'cddeposits of previous activity on tho slopes ofthe semi-cone.

The mechanism may have bee11 s imi18.r to the.: t Whichformed the caldera wall depos i ts of fragjilel1 t,'.ry m.::: terial inter­woven wiU1 sills and dykes mentioned on pace 2.,

Unusue.l activity Which resul ted in the fornE'. tion ofvolumi110US dus t and V2,'oour clouds occurl'ed be'cviecn 1745 and1800 hours on 31st January. The source, as seen from theobserva tion poin'c., ap:,?eared to be a series of vents in thedeeply disseci:.ed valle~T on '\:,he south side of the sGmi-conc.Figure 6 shows small vapour clouds at the commencement ofactivity and the lerge volume of v2.pour s.nd dus J(, subsoquentlydeveloped. The size of the cloud formed compared ':':i th thesmall dark cloud from the active crater (upper right handcorner in Figure 6b) sug~:ests that a largG volume of steam wasproduced indopenden'Cly of the main source of ac·i:.ivity. }Y:'onoises were heard at the obsorv,e.tion post. The activity li1ayhave resulted from slow-moving avalanches of ejected materi£.lreaching the top of a s teep"s'ided stream bed and collaps incinto pools of ~ater accumulated from previous heavy rains.bxamination of the lower parts of such an avalanche on 17thJanuary ravealed tha t the depos its main ta in hiGh tempt::r2 -Curesfor long periods. An inspection of the southern v~lley wasmade with binoculars from old lava depos its to the eas t on5th February; thermal activity 'Has not observed.

GROUl'TD 'l'IL'l; AND VOLCANIC EARTH9UAlillS..-._......~ • • ar"..,. ......·,;,a .... ... _ .....-.... •_~. ••,. _1-'__ ' ...-....-. ........;.a.~... __14 . ..•• __

A small concrete block used by Best in 1953 fortiltmeter readings was pointed out by nctive people ofWaris Village; it is situated just south of that villageand west of the path to the landing point. The area had'been overgrowl1, but was quiclcly cle2.red c.~l1d D. hut vrhichgave adequRte shelter from l~ain, was construc'~ed over theblock. Ins trwilents from Daiil Isl&nd wel~e ins t&lled on 26thJanuapy, '8.nd readings and I'ecords Viepe OO·CEI. ined fpom thenuntil 4th r.ebruary.

, .

Ape.rt from v8.riations due to atmosphc::..~ic tem])Cr2.tUl..... efluctua tions ~ no s ignific~mt trend was shown by the overalltil tme tel" readii1gs.

The pendulum mass was oriented to wive maximumdisplacement fOi' movements in G. north-south plane ~ i. e. fortremors 1'roIl1 the c::..'a tel.... area y the greater ampl i tude trsl1Sve=::rs ewaves would have=:: been recorded. OWing to the faulty clockdrive~ re=::cords for periods greater than about 15 minutes Der~

rarely obtained. For this reason 1 the shock recorder wasexamined frequently. No marks which could be attributed toground movements were observed on any of the records.

Father Aerni felt very slight y short period movementsin the mission quarters (a two storey building) a t the follo'.-'i.n rr

times -

January 11th12th13th

1845 - 1930 hours1530 hoursAll day.

He states~ however, that very strong winds from thenorth-wes t and strong surf pounding. the ilearby coas t may havecaused these movements.

Native people of the Tabele 9 Budua~ 0uris villages~

s i tua ted along the coas t on the southern to eas tern s ide ofthe island had felt no earth tr'emops during the activity• .iarispeople, however, stated that during the strong activity in InteDecember the ir hous es shook a t t~"mes of big eX:910s ions.

A bubble in the damping liquid of 2. priSm8."G1C com:92ssresting on a rock outcrop at the observation point vi~rated

slightly at the times of detonations st the crater. The vib­rations were possibly due to small ground waves ge:rer8.ted bythe explosions or by concussion effects against the steep wallsbene=::ath the observation point.

Although detone.tiolls 2t the crater occur::..'ed everyfew seconds, and the freclUel1c~T did ned; c118nge during theperiod of investigation~ a llwnber of fe.'.cts sug~~ested thatunless the:"'e was a change in the nature of the activity~ nodanger existed to the inhabitants of the island. 'I'hes~ fal;~~

are listed below -

1. ~jected material was deposited in erosion channels inthe 1946-47 deposits: aV~lanches followed the same pathas th8.t during 1946-47. No danger exis·i:.ed to nativevillages and gardens if this trend continued.

2. Most ejecta fell in the vicinity of the crater; thedanger area for this activi ty Vifas wi thin a mile radiusfrom the crater.

3. Dust and gas were not emitted in large volumes; gardenson the leeward side of the crater, the=::refore, were notlikely to be damaged.

4. There were no a'pparent ground movements vifhich SLg gesteddevelopment of more intense activity.

." . . ...

10.

'l.'hc J;>a ttel'l1 of ;,.... C·ClVl·Cy dur1.l1C previous erupti0i1Swas well l:novm to older peo:~)le in '~he vill::.~ges. P,o, ther DoehIn,who was Et Bieng Mis8ioj'1 on the north-'viTest coast of MEmr':JI1

Island for abou'G 30 years, ha.d [~lsoJ?assed on his 101OY/ledgeof Drevious el'uptions to the pa thers who i'eTllaced him. fl'heseautllOri'cies regarded 8.ctivi·cy i11 December 1956 to February 19578.8 mild; they expec 'Geel s trongeI' dc:vcloplilcn'GS ill the c oraingMayor June. 'rhe peo;)le were warned thc~ t C:L1Y unusual dcvelop­ments such &s comrne:ncemtmt of ear"cllqu2lces 01' obvious C;P01.li1dmovemcnt should be reported by radio to the VUlctmolocsis "G,Rabaul, i.nuuedia '~ely.

Best, J.G. 1 1953 - Report of invostig8.tion of volc~nic

activity Manam Islcnd, ~.N.G., April1953. ;B.ill:•.N.illo~B,£§~O_~l~J~~~.jL~q. 1953/68.