Upphaf eldgossins ( Heklu 1980*

Transcription

1 Ian Philip Hutchinson: Upphaf eldgossins ( Heklu 1980* lj6smyndum er 69 t6k af fjallinu. Med samanburdi vid loftmyndir, er teknar voru i 6gfst 1979, mafii athuga hvort pessi snj6br6d vari edlileg midad vi6 6rstima eoa hvort um 6venju mikla brddnun vari ad rada, og pii vegna M6r og fdlaga minum. Andrew hakkandi hita i fjallinu ddur en gosid McKenzie. voru valin sradi nordausrur h6fst. af Heklu eftir dbendingum jard- fredinganna lngvars Birgis Fridleifssonar og Hauks J6hannessonar. Svadid sem g skyldi rannsaka er milli enda Heklugjdr og Hestcildu. og nar yfir Raudkembinga og Skjdlkriar med hrauninu frd Fram a0 Verslunarmannahelgi vorum vid heppnir med redur og d heidum og s6lbjrirtum degi i lok jfli gengum vid d h6tind Heklu. Allt var med kyrrum kjrirum 6 fjallinu og snj6r var i sprungum og gji4m sem mr ndudust f gosinu Gufusladur stigu uppdr gjallinu i toppgignum og mrnntu 6 eldinn i idrum fjallsins. Pann tima sem vid dvdldum d Heklusl6dum t6k snj6inn ort upp i Vid h<if6um a0 mestu lokid vid kortlagninguna 6 undangengnum fjdrum vikum og iitti 69 medal annars eftir ad skoda sl6ttuna milli Raudkembinga og Skj6lkviahrauns. Ur pvi skyldi bata pann vidburdarika dag, 17. 6grist Pennan dag var loft alskija0. Skijahad var um 2000 m og dreif rir peim regn60a ri6ru hvoru. Um kl. 13 bar hag suo-sudaustan gola smiiskor frd Heklu yfir mig par sem g var staddur d slettunni 5,4 km fr6 Heklutindi (stadur I ii l. mynd). Tindinn sd eg pr6tt fyrir regni6. Verra var ad rigningin aftraoi mdr a0 skipta um filmu i myndav6linni minni, fyrr en um seinan er gosid var hafi6. Pad voru lj6tu mistdkin. nordvesturhli6um fjallsins og brddnudu i hann geilar. Petta md sjd d Eldgossins varo 69 fyrst var er mikill hvellur heyrdist frri fjallinu, pegar dg Eins og tidkast vid flesta hiisk6la purfa jardfredinemendur vid hilsk6lann i Oxford a0 standa skil ii jardfra0ikorti til ad fd grd'0u sina. Er hverjum og einum gert ad kortleggja 15 km'lands dn adstodar kennara. *Plitt hefur Helgi Torfason. leit bangad, s6st hvitur gufust16kur stfga upp r6tt suovestan vio hatindinn. \:nrliulr:prrtrrlurrr il l1 r). bls llj l8l

2 1. mynd. Kort af Heklu sem sinir hvar hofundur var staddur er gosi6 h6fst (l) og leioina Litaf svedinu me6 viakomu ri Rauduskdl (II) og i tjaldstadinn (III). Ar Fyrsta bomban lenti kl ; B: Snjdbrridnun i jfli-dgrist; C: Farvegur hlaups, sem rann niour hlidina meb hradanum 360 kn/klst. kl ; D: Farvegir leysingarvatns; E: Gufuuppstreymi pann 18. i4grist; F: Djripar grefur i sarrdinn eftir leysingarvatn; G: Gufubdlstrar kl bann 17. 6gist (sje 2. mynd); H: Gosi6 byrjar i Toppgig kl og sprungan rifnar til sudu$ og nordurs; J: Lengd sprungunnar kl ; K: Lengd sprungunnar kl Hraunid fr6 Skjdlkvium trd 1970 er sky1gt. - Map showing the authors position qt the beginning of the eruption (1, II and. III) and the timing of various events (A-K), Raunar var erfitt ad greina tindinn niikvemlega padan sem eg sto0. A 6rskammri stundu stigu gufust16karnir upp fr skijabykkninu sem grffoi yfir. Sidustu 20 minfturnar {yrir sprenginguna hafdi g ekki veitt fjallinu neina serstakathygli. Eg get pvi ekki sagt um, hvort eldgosid hafi byrjaa eitthvao fyrr med 16legri hatti en beim sem vakti athygli mina. Samkvamt frinu minu h6fst gosid kl sem var einni minftu of seint er g bar pad saman vid rafmagnsklukku Brirfellsvirkjunar i isakoti. en hrin var sdsd hiirr6tt. Sam- 176 kvamt bessu etti gosi6 ad hafa byrjad kl , nokkru sidar en almennt er talid. * Hdva0inn fr6 Heklu j6kst jafnt og Fdtt og liktist einna helst gni frd botuhreyfli. Dynkir fr6 sprengingum heyrdust ekki fyrr en um PaO bil * Skjdlfta vard fymt vart ii skiilftam@lum kl annar kl en kl f6r virknin aa aukast og verulega kl Gos er talib hefjast kl , en pd kom fram gos6r6i ii skjalftamelum (skv. P61i Einarssyni. Skjdlftabref Raun!isindastofnun HI). PV6.

3 2. mynd. Hekla frd norori kl , 17. iigrist 1980, i pann mund sem hlaup renna nidur vesturhli0arnar. Gufu leggur af hlaupinu bak vid Litlu-Heklu (0r) og hedina vestan hennar (M6fell). - Hekla seen from no h at hrs., 17th of August 1980, just after the "jdkulhlaup" (glacier burst) ca wheeled dov'n Heklas western slopes. Steam-clouds are seen rising from above Litla-Hekla (arrow) and the hillock west of it (M6fell), but no erudtive vents were there. Photo bv I. P. Hutchircon. klukkustundu si6ar, en peir eru taldir komi6 fr6 heitu leysingavatni, en ekki vera samfara hraunframleidslu. 56 pad gj6sandi eldgig. r6tt hefur eingdngu komid upp aska Eitt bad furdulegasta sem 69 vard fylsta klukkutimann. vitni a0, meoan eg fylgdist med Eftir nokkrar minritur f6r gufustr6kurinn a0 dokkna, vard fyrst brinleitur brunadi nidur fjallshlidina nordaustan upphafi gossins, var jokulhlaup sem og svo svartur. Briitt huldist efsti hluti vid Litlu-Heklu (1. og 2. mynd). fjallsins i6andi b6lstrum i allavega litabrigdum af brfnu, svdrtu og hvitu. skyjahulunni, i n6l m h:eo, og Vatnselgurinn braust nidur undan Samtimis bessum Iitabrig6um lengdist b6kstaflega valt nidur hli6ina, sem gossprungan til sudvesturs og hvitir hallar par um 20% (11"). A h. u. b. 10 gufub6lstrar stigu upp handan vid sekfndum brunadi hlaupvatnid 1 km Litlu-Heklu. A 2. mynd md einnig sje vegalengd og f6r med um 360 km/klst gufustrdka stiga upp einhversstadar i hraba. Pessi blanda af is og vatni Nafurholtshrauni, pa6 langt frii gossprungunni a0 beir hlj6ta ad hafa anburdi vid Litlu-Heklu giska g 6 myndadi holan s(valning og me6 sam- ad 177

4 3. mynd. Lj6smynd tekin af rimanum ii Rauduskril kl Gossprungan hefur enn ekki n6d fullri lengd. Takid eftir gufunum er stiga uppfrd vesturhlidum Heklu, par sem aurskridur og leysingarvatn renna nidur hlidina. - Photograph taken from the rim of the ctatet Raudaskdl at hrs. The eruption fissure has not reached its full length. Notice the steam rising from the west slopes of Hekla, where mudflows and meltwater flow downhill. Phory by L P. Hutchinson. pverm6l hans hafi verid um 50 m. Pessi holskeflulcigun hefur tnilega verid afleiding af seigju elgsins og vi6- niimsins vid hlidina ii sama hdtt og pegar oldur brotna vid sj6varstrond. Holskeflan f ll svo saman og hvarf m6r sj6num handan vio Hringlandahraun. Pad leyndi s6r ekki ad tdluvert vatnsmagn var parna d feroinni. Fyrstu hraunkriluna sii 69 smjliga niour fr skijahulunni um pad bil 10 minrltum eftir ad gosid h6fst. Hfn lenti ri jordinni um bad bil 700 m vestan vio hnfkinn i Raudkembingum sem merktur er med ha0artolunni 931 m. Petta var sterdar flykki, nlla'gt 2 m i bvermdl, kont6tt og liktist ftemur broti (r hraunriisinni en kvikuslettu. i sdmu andrd hvolfdist svart og hrjfft oskuregnia yfir mig. Hraunkrilurnar voru egglaga og allt a0 30 cm langar. Megnid af oskunni kom rir hraunkril um, sem splundrudust ii jordinni og var kornastaroin um 5 cm. Askan var oll ldttari en hfn leit rit fyrir a0 vera, vegna pess hve blodrcitt hfn var. lnnst i hraunkflunum voru blodrurnar allt ad 2 cm i pverm6l, en f6ru minnkandi er kom ner sl6ttu ytrabyroinu sem var sprungio, eins og midjan hafi haldid 6fram ad b6lgna, eftir ad skurn hafoi myndast yst. Engir dilar siiust i dskunni. Um pao bil 35 hraunkrilur f6llu ri hvern fermetra 6 minitu. 178

5 4. mynd. Vi6 tjaldstabib 18. 6grist. Gj6skumolinn sjnir gr6fleika Sskunnar ofan6 tjtildunul'tr. - At the campsite lsth of August. The handspecimen shot,s the gruinsize of the tephra trhich buried our tents- Photo bj I. P. Hutchinson. Pegar hdr var komio fannst m6r semast a6 hypja mig og t6k til f6tanna ( 6ttina a0 Rau0uskril, med kortatoskuna til hlifbar yfir h6f6inu. Skynja6i 69 br:itt i hvilikri hettu 69 var staddur. Eg t6k 3. mynd um kl fr6 barminum 6 Rau6uskril. Var pr4 sem biksvdrt tjdld staou eftir endilangri Heklugj6. Oskufallid j6kst nf sifellt og gosmrikkinn lagdi beint yfir mig svo a6 dimmdi nestum eins og af n6ttu. Peirri hugsun skaut upp ad fleygja einhverju af hafurtaski minu. En i pvi var afrakstur fjogurra vikna kortlagningar og ranns6kna, auk lj6smynda, svo ao 69 visadi peirri hugsun fra. Ferdin ni6- ur af Rauduskdl var glannaleg i nffallinni ciskunni, sem pykkna0i 60um. p6tt m6r hef6i nf skilaa talsvert 6 leio, var pad versta enn eftir, en pab 179 var ad komast yfir Skj6lkviahraun. Einhvern veginn stauta6i ig p6 iifram, hdlfblinda6ur i sortanum, yfir 6jdfnurnar ( pessu gamla hrauni. Eg var a0 missa allt attaskyn og 6tti erfitt aa f6ta mig ( nffallinni oskunni. Ofan af hraunhryggjunum grillti 69 um s(oir i d<ikkan jadar hraunsins frd og dg vissi ad tjaldsta6i6 var abeins 300 m i vestur fr6 noraaustustu totunni. Pegar 6g kom ab tioldunum kl bei6 Andrew par med v6lhj6li6. Oskuregnid hafdi tett I sundur himininn 6 birgdatjaldinu og st6rskemmt stdra tjaldid okkar. Medan vid vorum par inni ad tina saman naubsynlegustu pjdnkur okkar, fdll st6r hraunkrila 6 m?enis6sinn og mdlbraut hann og vio s6um ad bedi tjdldin hlytu aa eydileggjast. 0tifyrir hafoi t6nninn i

6 5. mynd. A stiflunni vid Isakot kl ,17. 6gist. Fdeinir senrimetrar af risku (50 mm i Fvermal) hylja stiflug6lfi0 (vid handridi0 er v6lhj6lid 966a). - Ar Birfetl dam (isakot) at hrs. the 17th of August. Several cm of tephra (grainsize 50 mm) corer the dam Jlool (our dear motorbike at the fence). Photo by I. P. Hutchinson. Heklu breyst. I stadinn fyrir stddugan byt komu drunur og hvellir med fiieinna sekrindna millibili. Raudir bjarmar listu gegnum sortann og eldingar Ieiftrudu yfir okkur. Vid purfrum ad fylla d tankinn d v lhj6linu og mikid reid d ad ekki kemust 6hreinindi i bensinid, pvi pri myndi hj6lid drepa ii s6r. Pegar pad f6r i gang eftir tiu drvantingadullar tilraunir, fyrirg6fust allir pess fyrri dyntir. Er vid logdum af sta6 var begar fallin pad mikil aska a0 illmdgulegt var Solvahraun versnaoi 6standi6 enn, er tok ad hellirigna. Askan vard ad vatnsblandaori pungri ledju sem sardi okkur i framan og klesstist kringum augun. Med rigningunni h6fust eldingarnar aftur og laust milli dokkra b6lstranna, 6hugnanlega liigt. A fullri fer6 ni4dum vid loks rit rir versta dskuregninu, n6lagt vegam6tunum upp i Sigrildu. Nokkrum kilometrum nordar var Isakot, mdr varo lj6st ad 69 var sloppinn rir mestu eldraun afi minnar. Vid isakotsstifluna hittum vid vini ad fylgja sl66inni upp 6 Fjallabaksveg. okkar, sem vid hcifoum kynnst miinud- ii undan. Skilabod voru send um Prau fyrir hdvadann i hljodkftslausuinn v6lhj6linu, sem svo oft hafdi raskad ad okkur vari borgid og vid pridum fjallakyrrdinni h6r, gdtum vi6 heyrt meo pokkum bo6 um mat og husaskjdl nastu vikuna. Nasta dag dynkina lrd Heklu, Er vid komum i forum 180

7 vid iisamt f6ltigum okkar til ad bjarga pvi sem eftir var af blautum og skitugum tjdldunum og vio a0 sja tatlurnar af peim ur6um vid srelustu fl6ttamenn sem um getur. Vid f6lkid i Bnrfetlsvirkjun stondum vio i avarandi pakkarskuld fyrir gestrisnina. The Eruption of Hekla 1980 Ian P. Hutchinson, could still see the summit despit the weather. This rain delayed the reloading Department of Geology, of my camera until after the start of the Unive rs ity of W itwatersrand, eruption - a serious error in retrospect. I Jan Smuts Avenue, The first I knew of the eruption was a Johannesburg 2001, loud bang from the mountain. When I South Africa looked up I saw a column of white steam rise from slightly southwest of lhe summit. In common with most universities, the but from my angle of sight it was hard to Oxford geology degree course requires the judge where the summit was. This column submission of a field mapping report. For of steam quickly penitrated the cloud this. one has to individually map the geology of an area, 15 km'. With help from possibly 20 minutes prior to the explosion cover. I had not consciously observ d for Drs. I. B. Fridleifsson and H. J6hannesson suitable areas northeast of Hekla were quiet etfusive activity before it. I timed the so I can not say whether there was any chosen for myself and my colleague start of the eruption at 13:30 hours on my Andrew McKenzie. My area lay between watch which turned out to be one minute the end of Heklugjii and Hestalda, slow when compared with what was said to incoryorating Raudkembingar and Skj6lkviahraun with the 1970 volcanics. Power Station Dam. This makes mv star- be a correct electronic watch at the Bfrfell Up to the August Bank Holiday we ting time 13:31 houls - somewhat different to the official one (13:27 hours). were lucky with the weather and on a clear, sunny day at the end of July we The noise that followed was an climbed ro Hekla s summit. All was quiet increasingly loud roaring sound similar in on the mountain, and snow filled the fissures of the previous eruption in The individual detonations and none were quality to a jet aeroplane. There were no simmering power within the volcano was heard until about an hour later. Detonations occur only with the production of only betrayed by wisps of steam rising from the rubble walls of the summit crater. lava. This first hour must have produced During my stay in the area the snow on Hekla's northwest flank had shown signs of pregressive melting and crevassing. This can be seen on my photographs of the mountain. Comparison of these with aerial photographs of the area taken in August 1979 could say whether this melting was seasonal or exceptional, ie. due to a preeruption intemal temperature rise. The four weeks prior to the eventful day had seen most of the work completed and only a few areas such as the plateau between Raudkembingar and Skjdlkviahraun remained to be mapped. This was the task for the 17th August There was a contiuous low cloud cover at an altitude of about 2000 m with intermittent periods of fine rain. At l3:00 hours a slight NNE breeze carried a small shower from over Hekla to where I was standing on the plateau (map reference: ), 5.4 km from the summit. I only tephra. Minutes later the steam turned a dirty brown colour and then black. Soon the entire summit was enr eloped in billowing clouds of all shades. Meanwhile, the eruption was spr ading away from me along the fissure and isolated white mushroom clouds appeared from behind Litla-Hekla. On the photographs (fig I and 2) one mushroom cloud can be seen to rise due west of my position. So great is its appa- 181

8 rent distance from the fissure - ie. somewhere on Nefurholtshraun - that it must be due to the collection of boiling water from the volcano's flanks and not an erupting vent. The most striking thing I was to witness du ng the eruption was a glacier burst down the northwest flank of Hekla, northeast of Litla-Hekla. The water broke through the clouds, which were now as low as the 1000 m level. and literalll 'cartwheeled down the 20'. 5lope covering a distance of 1km in about 10 seconds; a speed of 360 km/h (225 mph.). The water/ ice formed a hollow cylinder and from its size relative to Litla-Hekla, I estimate its diameter to have been around 50 m. This penomenon was presumably the product of viscosity and basal ftiction effects stmllar to those found in waves breaking onto a beach. The cylinder had collapsed before it passed out of sight behind Hringlandahraun. The volume of material involved was considerable. About ten minutes after the start of the eruption I saw the first bomb arc through the overlying cloud and strike the ground some 700 m west of the 931 m summit in Raudkembingar. It was large in the order of two metres - and angular, more like a piece of volcanic breccia ripped off the side of the fissure than juvenile, molten rock. Within seconds, I was being showered with black, crusty tephra. The whole bombs were ovoid in shape and up to 300 mm long. The majority of the tephra were fragments of bombs about 50 mm in size. Because of the extremell high vesicularity. the tephra was lighter than it looked. The vesicles were upp to 20 mm diameter in the cenlre of the bombs but their size decreased towards the edges which were smooth but fractured as if the insides had continued to swell after the outer skin had formed. No phenocrysts were visible in the tephra. They were falling at a rate of 35 impacts per square metre per minute At this point I thought it prudent to fallen that it became near impossible to withdraw from the scene and set off across follow the fast disappearing track back to the plateau at a healthy trot in the direc- the Landmannalaugar road. The explo- tion of Raudaskdl with my mapcase protecting my head. Photograph (fig 3) was taken from the rim of Raubaskdl at about 13:50 hours and by then a black curtain seemed to stretch the length of Heklugjri. The ash fall became much greater and with the eruption column directly overhead it was nearly as black as night. At this point I considered shedding some excess weight but as this included four weeks-worth of field map and notes as well as my photographs I decided against it. Even though I was now nearer to my goal, the trip across Skj6lkviahraun was the worst I was to experience. The darkness and low visibility left me stumbling blindly over the hummocks in the old lava flow. I was fast losing my sense of direction and staying on my feet was becoming difficult because of the unconsolidated ash. At the top of each rise I could just see the black outline of the 1970 lava and I knew that when I reached its northeast tip the camp lay only 300 m to the west When I arrived at the camp about 14:20 hours, Andrew as already there with the vehicle. Tephra had ripped the nylon flysheet of the stores tent to shreads and severely damaged the cotton of the large tent. Whilst inside, collecting a few things together for the evacuation, a large piece of tephra broke the ridge pole and we realised that both tents were probably writeoffs. Outside, the noise from Hekla changed. The steady roar became more of a rumble with detonations every few seconds. Red 'fires' could be seen through the blackness and lightning flashed low over our heads. Before we could leave, we had to refuel the motorbike. One speck of dirt or badly mixed petrol and oil in the tank would leave us stranded. I never had much faith in its mechanical reliability but after it sta ed on the tenth desperate kick I forgave its previous idiosyncrasies. By the time we set off, so much ash had 182

9 sions from Hekla could be easily heard over the din from the unsilenced motorbike which usually shattered the peace of this countryside. On Sdlvahraun, the conditions were aggravated by heavy rain that mixed with the ash making it heavier, so that it cut your face and stuck round your eyes. The rain brought the lightning back with it, which leaped amongst the black clouds frighteningly low. With the thrcttle wide open we finally left the worst of the ashfall near the junction with the Sigalda road. Bfrfell Power Station Dam lav onlv a few kilometres to the north and I knew that the greatest ordeal of my life was over. At the dam we were met by the friends we had got to know over the past month. Messages of safe-return were sent and offers of food and shelter for the next week were gratefully received. The next day we vent with our friends to salvage the sodden and filthy remains of our camp the look of which made us the most welcome of refugees. For the hospitality of all the people at Brirfellsvirkjun, we are for ever in their debt. 183