By Bill McGuire
I know that if I ask someone to name a single volcano, the chances are that they will hit upon Krakatoa; such is the degree to which the cataclysmic 1883 blast of the volcano has etched itself into the public consciousness. Remotely located in the Sunda Strait, between the Indonesia islands of Sumatra and Java, the islands that made up the long-dormant volcano were pretty much unheard of prior to August, 130 years ago, when all hell broke loose. In fact the locals had been aware that something was not quite right with Krakatoa for quite a while. Swarms of small earthquakes had been periodically shaking the volcano for years until, in May 1883, the bursting open of steam vents on the flanks testified to the presence of fresh magma close to the surface. Activity increased in fits and starts over the next few weeks until, by mid-June, violent blasts were expelling columns of ash and pumice several kilometres into the atmosphere.
The climactic, paroxysmal, phase of the eruption began in earnest just after mid-day on the 26th of August, when a sequence of titanic explosions, heard all over Java, propelled a column of black ash and pumice to heights of more than 25 km. Even these, however, were dwarfed by what happened the following day. Although difficult to be certain, it looks as if the expulsion of vast quantities of magma had left the volcano structurally unstable so that it began to collapse in upon itself, allowing seawater to pour into the magma chamber. The violent fusion of molten rock and cold water triggered a detonation so ear-splitting that some have speculated that it may have been the loudest noise in recorded history. Whether true or not, its volume was sufficient to transmit the sound an astonishing distance; as far, in fact, as Alice Springs, 4,600km away in the heart of Australia. To put this in a European perspective, if the explosion had occurred in the Canary Islands, it would have been heard as far away as Liverpool and Copenhagen. Such was the shock to the planet’s atmosphere that the resulting pressure spike registered on barometers around the world as it circled the planet four times before dissipating.
At the same time that the detonation blasted magma upwards, it spawned colossal flows of hot ash, pumice, and debris that cascaded down Krakatoa’s flanks, displacing the surrounding waters of the Strait and promoting the formation of giant tsunamis. Within minutes, more than 160 communities on neighbouring coastlines were swamped by the sea. For the inhabitants, there was no escape from the unstoppable waves. At Anjer, on the east coast of Java, they were as high as the 40m lighthouse, which they brought crashing down. In all, this terrible conspiracy of the gods of the sea and the underworld — Neptune and Vulcan — consigned more than 36,000 people to their graves, making the eruption the second most lethal of the last 250 years.
The legacy of the blast did not, however, end there; the millions of tonnes of fine ash and sulphur particles ejected into the atmosphere reflecting sunlight back into space and causing temperatures across the globe to plunge by more than 1°C. Astonishingly, a similar cooling effect on the oceans could still be detected well into the twentieth century. Another bequest of the dust and gas scattered throughout the stratosphere was a spectacular atmospheric display that incorporated crimson, purple, and yellow sunsets alongside coloured suns and moons including – in the latter case – the blue variety.
However unprecedented the 1883 blast may have seemed to those in Europe and North America, to whom newly installed undersea telegraph cables brought news of the catastrophe within hours, it is worth bearing in mind that, from a geological point of view, the Krakatoa eruption was pretty small beer. In fact, it wasn’t even the biggest of the 19th century; that honour going to the 1815 eruption of another Indonesia volcano, Tambora, which was 3–4 times bigger and that killed approaching 100,000 people. This event had an even greater impact on the global climate, to the extent that the following year is renowned — in Europe and North America — as the ‘year without a summer’; an episode of widespread crop failures that triggered the last, great, subsistence crisis in the western world. Looking further back in time, the Krakatoa explosion is dwarfed by the great super-eruptions that shake the planet a couple of times every 100 millennia. The stupendous blast that tore open a 100 km hole in Sumatra around 74,000 years ago, for example, dumped ash across one percent of the planet’s surface, plunged our world into volcanic winter, and was more than 100 times bigger.
The anniversary of the 1883 Krakatoa blast is perhaps a good time to think about what future volcanic activity may hold in store for us, particularly as it is now nearly a quarter of a century since the last eruption big enough to give a volcanologist, like myself, sweaty palms. As regards where the next big bang will occur, your guess is as good as mine. Somewhere out there beneath one of the world’s 1500 or so active volcanoes I can guarantee, however, that pressure is building prior to unleashing an explosion that will put that of 1883 in the shade. Whether we have to wait a year, a decade or a century or more, it really is just a matter of time.
Bill McGuire is an academic, science writer, and broadcaster. He is currently Professor of Geophysical and Climate Hazards at UCL. Bill was a member of the UK Government Natural Hazard Working Group established in January 2005, in the wake of the Indian Ocean tsunami, and in 2010 a member of the Science Advisory Group in Emergencies (SAGE) addressing the Icelandic volcanic ash problem. He was also a contributing author on the recent Intergovernmental Panel on Climate Change (IPPC) report on extreme events. His books include Waking the Giant: How a changing climate triggers earthquakes, tsunamis, and volcanoes, Surviving Armageddon: Solutions for a Threatened Planet, and Seven Years to Save the Planet. Read his previous blog posts.
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Image credit: Krakatoa eruption 2008. Public domain via Wikimedia Commons
"Bill McGuire aliandika: ""Ninajua kwamba ikiwa nitamwuliza mtu jina la volkano moja, kuna uwezekano kwamba watagonga Krakatoa, kiwango ambacho mlipuko wa 1883 wa volkano umejishika katika fahamu ya umma.""" Kisiwa hicho kilichopo katika Mlango-Bahari wa Sunda, kati ya visiwa vya Sumatra na Java, kilikuwa ni kisiwa kisicho na watu kabla ya mwaka wa 130 iliyopita, wakati moto ulipoanza kuwaka. Watu wa Krakatoa walikuwa na wasiwasi kwamba kulikuwa na kitu kibaya na Krakatoa. Kwa miaka mingi, tetemeko la ardhi dogo-dogo lilikuwa likitikisa volkano hiyo kwa ukawaida, mpaka Mei 1883, wakati milango ya mvuke iliyofunikwa kwenye pande za volkano hiyo ilipofunguka, ikathibitisha kwamba kulikuwa na magma safi karibu na uso. Utendaji huo uliongezeka kwa vipindi katika majuma machache yaliyofuata hadi katikati ya Juni, milipuko mikali ilipokuwa ikipeleka nguzo za majivu na mawe ya pumice kilometa kadhaa ndani ya angahewa. Mlipuko huo ulizuka kwa nguvu baada ya saa sita mchana tarehe 26 Agosti, wakati mfululizo wa milipuko mikubwa, iliyosikika kote Java, ilisababisha safu ya majivu na mawe ya pumice ya rangi nyeusi kufikia urefu wa zaidi ya kilomita 25. Hata hivyo, hata hayo yalipuuzwa na yale yaliyotokea siku iliyofuata. Ingawa ni vigumu kuwa na uhakika, inaonekana kama kwamba kutolewa kwa kiasi kikubwa cha magma kuliacha volkano hiyo isiyokuwa imara kiundani hivi kwamba ilianza kuanguka ndani yake yenyewe, ikiruhusu maji ya bahari kuingizwa ndani ya chumba cha magma. Mvutano huo wa mawe yaliyoyeyuka na maji baridi ulisababisha mlipuko mkubwa sana hivi kwamba baadhi ya watu wamedai kwamba huenda ulikuwa sauti kubwa zaidi kuwahi kurekodiwa katika historia. Kwa kweli, sauti ya sauti hiyo ilisambazwa kwa umbali wa umbali wa Alice Springs, umbali wa kilomita 4,600 kutoka Australia. Kwa mfano, ikiwa mlipuko huo ulikuwa umefanyika katika visiwa vya Canary, ungeweza kusikika mbali kama vile Liverpool na Copenhagen. Mlipuko huo ulisababisha mlipuko mkubwa wa hewa katika anga ya sayari hiyo, na barometers za dunia nzima ziliona mlipuko huo ukizunguka sayari hiyo mara nne kabla ya kupotea. Wakati huohuo, mlipuko huo uliposababisha magma kuanguka, ulitokeza mtiririko mkubwa wa majivu moto, mawe ya pumzi, na mabaki yaliyotiririka chini ya miamba ya Krakatoa, na kuhamisha maji ya karibu ya Mlango-Bahari na kuchochea kuundwa kwa tsunami kubwa. Katika dakika chache tu, zaidi ya jamii 160 kwenye pwani jirani zilifunikwa na bahari. Kwa wakazi, hakukuwa na njia ya kutoroka mawimbi hayo yasiyoweza kusimamishwa. Anjers, katika pwani ya mashariki ya Java, ilikuwa na urefu wa mita 40 na ilishuka kwa kasi. Kwa jumla, njama hii ya kutisha ya miungu ya bahari na ulimwengu wa chini ya ardhi - Neptune na Vulcan - ilifanya watu zaidi ya 36,000 waangamie makaburi yao, na kufanya mlipuko huo kuwa wa pili wenye kuua zaidi katika miaka 250 iliyopita. Hata hivyo, athari za mlipuko huo hazikukoma hapo; mamilioni ya tani za majivu na chembechembe za sulfuri zilitupwa angani, zikirudisha mwangaza wa jua angani na kusababisha joto duniani kote kupungua kwa zaidi ya 1 ° C. Kwa kushangaza, athari kama hiyo ya baridi kwenye bahari bado ingeweza kugunduliwa hadi karne ya ishirini. Uharibifu mwingine wa vumbi na gesi zilizotawanyika katika angahewa la angahewa ulikuwa maonyesho ya kuvutia ya angahewa yaliyohusisha machweo ya jua ya rangi nyekundu, zambarau, na manjano pamoja na jua na mwezi wenye rangi, kutia ndani - katika kisa cha mwisho - aina ya bluu. Hata kama mlipuko wa mwaka 1883 ulionekana kuwa usio na kifani kwa wale walioishi Ulaya na Amerika Kaskazini, ambao waya za telegrafu zilizowekwa chini ya bahari zilikuwa zikiwapelekea habari za msiba huo kwa muda wa saa chache tu, ni muhimu kukumbuka kwamba, kwa maoni ya kijiolojia, mlipuko wa Krakatoa ulikuwa wa ukubwa mdogo sana. Kwa kweli, haikuwa hata kubwa zaidi ya karne ya 19; heshima hiyo inakwenda kwa 1815 mlipuko wa volkano nyingine ya Indonesia, Tambora, ambayo ilikuwa mara 3 4 kubwa na ambayo iliua watu karibu 100,000. Tukio hili lilikuwa na athari kubwa zaidi kwenye hali ya hewa ya ulimwengu, kwa kiwango ambacho mwaka uliofuata unajulikana - huko Ulaya na Amerika Kaskazini - kama "mwaka bila majira ya joto"; kipindi cha kushindwa kwa mazao kwa wingi ambayo ilisababisha mgogoro wa mwisho, mkubwa, wa kuishi katika ulimwengu wa magharibi. Kwa mujibu wa utafiti huo, mlipuko wa Krakatoa ni mdogo kuliko milipuko mikubwa ambayo hutikisa sayari mara kadhaa kila baada ya miaka elfu moja. Mlipuko mkubwa uliofungua shimo la kilomita 100 huko Sumatra miaka 74,000 iliyopita, kwa mfano, ulitupa majivu juu ya asilimia moja ya uso wa sayari, na kuingiza ulimwengu wetu katika majira ya baridi ya volkano, na ilikuwa kubwa zaidi ya mara 100. Mwaka 1883 Krakatoa mlipuko ni wakati mzuri wa kufikiria nini shughuli ya baadaye ya volkano inaweza kuwa na hifadhi kwa ajili yetu, hasa kama ni sasa karibu robo ya karne tangu mlipuko wa mwisho kubwa ya kutosha kutoa volkanoolojia kama mimi, mikono sweaty. Kuhusu mahali ambapo mlipuko mkubwa ujao utatokea, nadhani wewe ni mzuri kama mimi. "Hata hivyo, mahali fulani chini ya mojawapo ya volkano 1500 au zaidi zinazofanya kazi ulimwenguni, ninaweza kukuhakikishia kwamba shinikizo hilo linaongezeka kabla ya kutokeza mlipuko ambao utaweka ule wa 1883 katika kivuli.""" Kama tunapaswa kusubiri mwaka, miongo, karne au zaidi, ni suala la muda tu. Bill McGuire ni mwanafunzi, mwandishi wa sayansi, na mtangazaji. Yeye kwa sasa ni Profesa wa Geophysical na Hali ya Hewa Hatari katika UCL. Bill alikuwa mwanachama wa Serikali ya Uingereza Natural Hatari Working Group ilianzishwa Januari 2005, baada ya tsunami Bahari ya Hindi, na mwaka 2010 mwanachama wa Sayansi Advisory Group katika dharura (SAGE) kushughulikia Icelandic volkano majivu tatizo. Pia alikuwa mwandishi wa mchango kwenye ripoti ya hivi karibuni ya Intergovernmental Panel on Climate Change (IPCC) juu ya matukio ya hali ya juu. Vitabu vyake ni pamoja na Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis, and Volcanoes, Surviving Armageddon: Solutions for a Threatened Planet, na Seven Years to Save the Planet. Soma machapisho yake ya zamani ya blogu. Kujiunga na OUTPlog kupitia barua pepe au RSS. Kujiunga na makala ya sayansi ya dunia na maisha tu kwenye OUPblog kupitia barua pepe au RSS. Picha: Mlipuko wa Krakatoa 2008 Eneo la umma kupitia Wikimedia Commons