Amagagasi Abulalayo—Izinganekwane Namaqiniso

KWASE kuyimizuzwana ilanga lishonile. Ngalolu Lwesihlanu oluthule, ngo-July 17, 1998, amadoda, abesifazane nezingane basemadolobhaneni ambalwa asogwini olusenyakatho lwePapua New Guinea bethuswa ukuzamazama komhlaba okunamandla angu-7,1. “Ukugadla kokuqala,” kusho i-Scientific American, “kwashaya amakhilomitha angu-30 ogu . . . futhi kwacekela phansi indawo engasogwini lolwandle. Ulwandle oluvame ukuba yisicaba lwakhuphuka, lwabangela igagasi elikhulu (tsunami) elisabekayo.”

Owabona lesi senzakalo uthi wezwa okwakuzwakala njengokuduma kwezulu buqamama, okwaya kuncipha njengoba amanzi olwandle ayehla aze aba ngaphansi kophawu oluvamile. Ngemva kwemizuzu embalwa, wabona igagasi lokuqala, elalingaba amamitha amathathu ukuphakama. Lamfica lapho ethi uzama ukubaleka. Igagasi lesibili, elalilikhulu, laqothula idolobhana lakubo futhi lamthatha layomntshinga ebangeni elingaba yikhilomitha, ehlathini lomhlume eliseduze. I-Science News iyabika: “Imfucumfucu eyayilenga ezihlahleni zesundu yayibonisa ukuthi amagagasi aphakama aba ngamamitha angu-14.”

Ngalolo suku amagagasi amakhulu abulala okungenani abantu abangu-2 500. Isimanga ukuthi kamuva inkampani egawula imithi yanikela ngezingodo zokwakha izikole ezintsha, kodwa zazingasekho izingane ezazizoya esikoleni. Cishe zonke—ezazingaphezu kuka-230—zazibulawe yi-tsunami.

Ayini Ama-tsunami?

Elithi tsunami yigama lesiJapane elisho “igagasi letheku.” Incwadi ethi Tsunami! ithi leli “yigama elifanelekayo, ngoba la magagasi asabekayo avame ukubangela ukufa nembubhiso emathekwini nasemadolobhaneni angasogwini eJapane.” Yini eyenza la magagasi asabekayo abe namandla futhi abe makhulu ngale ndlela?

Ngezinye izikhathi ama-tsunami abizwa ngokuthi ukungenisa kolwandle. Nokho, uma sesikhuluma iqiniso, ukungenisa kolwandle kumane kuwukukhuphuka nokwehla kwamagagasi futhi kubangelwa amandla adonsela phansi elanga nenyanga. Ngisho namagagasi amakhulu—ngezinye izikhathi angamamitha angu-25 ukuphakama—abangelwa umoya onamandla, awalutho uma eqhathaniswa nama-tsunami. Uma ubungabhukuda ungene ngaphansi kwala magagasi, ubuyothola ukuthi amandla awo ayancipha njengoba ujula. Ekujuleni amanzi awaphazamiseki ngisho nakancane. Kodwa akunjalo ngama-tsunami. Amandla awo asuka phezu kobuso bamanzi ayosho ekujuleni kolwandle, ngisho nakuba amanzi engamakhilomitha amaningi ukujula!

I-tsunami ijulile ngenxa yokuthi ngokuvamile ibangelwa ukuzamazama okunamandla okwenzeka ekujuleni kolwandle. Ngenxa yalokho, ngezinye izikhathi ososayensi babiza ama-tsunami ngokuthi amagagasi okuzamazama komhlaba. Indawo ephansi ekujuleni kolwandle ingase ikhukhumale, iphakamise amanzi angaphezulu abe yigquma, elingase lihlanganise indawo engamakhilomitha-skwele angu-25 000. Noma indawo esekujuleni kolwandle ingase izike, imbe umgodi wesikhashana olwandle.

Kungakhathaliseki ukuthi yikuphi, amandla adonsela phansi enza amanzi enyuke aphinde adambe—isimo esibangela uchungechunge lwamagagasi, njengalawo aba khona uma uphonsa itshe exhaphozini. Lesi simo sichitha inganekwane ethandwayo yokuthi ama-tsunami ayigagasi nje elilodwa elinamandla. Kunalokho, ngokuvamile abangela uchungechunge lwamagagasi. Ama-tsunami angase abangelwe nawukuqhuma kwentaba-mlilo noma ukugidlika kwenhlabathi ngaphansi kolwandle.

Uchungechunge olubi kakhulu lwama-tsunami aziwayo emlandweni lwenzeka ngo-August 1883 ngemva kokuqhuma kweKrakatau, intaba-mlilo yase-Indonesia. Amanye amagagasi akheka lapho afinyelela amamitha angu-41 ukuphakama ngaphezu kogu lolwandle futhi akhukhula amadolobha namadolobhana angasogwini angaba ngu-300. Kungenzeka ukuthi inani labantu abafa lalingaphezu kuka-40 000.

Izici Ze-tsunami Ezimbaxa-mbili

Amagagasi apheshulwa umoya awahambi ngesivinini esingaphezu kwamakhilomitha ayikhulu ngehora, futhi ngokuvamile ahamba kancane kakhulu kunalokho. Incwadi i-Tsunami! ithi: “Ngakolunye uhlangothi, amagagasi e-tsunami angagijima njengendiza, ngesivinini esethusayo esingaphezu kwamakhilomitha angu-800 ngehora noma ngaphezulu ekujuleni kolwandle.” Nokho, naphezu kwesivinini sawo, awayona ingozi ekujuleni kolwandle. Ngani?

Okokuqala, ngenxa yokuthi phakathi olwandle, igagasi elilodwa ngokuvamile lingaphansi kwamamitha amathathu ukuphakama; kanti okwesibili, igagasi lingase libe nezikhawu zamakhulukhulu amakhilomitha, okulenza liphakame kancane kancane. Ngenxa yalokho, ama-tsunami angadlula ngaphansi kwemikhumbi kodwa angaqapheleki. Induna yomkhumbi owawumi ngasogwini lwesinye seziQhingi zaseHawaii yayingaboni ngisho nokuthi kwakudlule i-tsunami kwaze kwaba yilapho ibona amagagasi amakhulu egasela ugu ebangeni eliqhelile. Ngokuvamile ukuphepha olwandle kuxhomeke ekutheni imikhumbi ifinyelele endaweni enamanzi ajule okungenani ngamafathomu ayikhulu, noma amamitha angu-180.

Ama-tsunami ayashintsha lapho esondela ogwini ngasemanzini angajulile. Lapha, ukushayisana nephansi lolwandle kubamba igagasi—kodwa hhayi lonke. Ingemuva legagasi njalo lisemanzini ajulile kunengxenye engaphambili, okulenza lihambe ngokushesha. Eqinisweni, igagasi liyanqwabelana, liphakame njengoba linciphisa isivinini. Phakathi naleso sikhathi, kufika amagagasi alandelayo kulolu chungechunge, ashayisane namagagasi angaphambili.

Ekugcineni, ama-tsunami angase ehlele ogwini njengamagagasi anamandla noma njengodonga lwamanzi okuthiwa i-bore, kodwa ngokuvamile, aqhamuka njengesikhukhula esenyuka ngokushesha esiba ngaphezu kwesilinganiso samanzi avamile. Amanzi enyuka abe ngaphezu kwamamitha angu-50 phezu kogu lolwandle futhi athwala imfucumfucu, izinhlanzi ngisho nezixhobo zama-coral izinkulungwane zamamitha azikhukhulele ezweni, abhubhisa konke okusendleleni yawo.

Okukhohlisayo ukuthi uphawu lokuqala lokusondela kwe-tsunami akuwona ngaso sonke isikhathi amanzi enyukayo asondela ngasogwini. Kungase kube yisimo esiphambene nalokho—ukuncipha kwamanzi okushiya amabhishi namatheku engenalutho nezinhlanzi zisale dengwane esihlabathini noma odakeni. Okunquma ukuthi isimo siyoba yini yingxenye yamagagasi efika ogwini kuqala—ukungenisa kolwandle noma ukudamba kwalo.a

Lapho Ibhishi Loma

Kwakupholile kusihlwa ngo-November 7, 1837, esiqhingini saseHawaii iMaui. Incwadi i-Tsunami! ichaza ukuthi cishe ngehora lesikhombisa kusihlwa, amanzi aqala ukudamba ebhishi, embula izixhobo zama-coral nezinhlanzi zasala dengwane. Izakhamuzi eziningi zesiqhingi ezazijabule zagijima ziyocosha izinhlanzi, kodwa abantu abayidlanzana, ababeqaphile, babalekela endaweni ephakeme, mhlawumbe bazi kokwake kwenzeka ukuthi yini eyayisondela. Ngokushesha, kwafika isikhukhula esisabekayo sakhukhula lonke idolobhana elinezindlu ezingu-26, kanye nezakhamuzi nemfuyo, sayokulahla echibini elincane elaliqhele ngamamitha angu-200 ezweni.

Ngabo lobo busuku, izinkulungwane zabantu zazibuthene ebhishi kwesinye isiqhingi zizobamba inkonzo yesonto. Nalapho futhi, ukudamba kwamanzi ngokungazelele kwabangela izakhamuzi zaseHawaii ezinelukuluku ukuba zigijimele ebhishi. Khona-ke, kwavela igagasi elikhulu elingamamitha ayisithupha ukuphakama “elalishesha njengehhashi lomjaho,” ngokusho kwesinye isibukeli. Amanzi ayehoxa adonsa ngisho nezinhlambi ezinekhono azifaka phakathi olwandle, lapho abaningi bagwiliza khona ngenxa yokukhathala.

Ahlasela Kaningi Kangakanani?

I-Scientific American ithi: “Kusukela ngo-1990, ama-tsunami ayishumi aye abulala abantu abangaphezu kuka-4 000. Sekukonke, kwabikwa angu-82 emhlabeni wonke—inani eliphakeme kakhulu kunenani ebelibikwa kuwo wonke umlando langu-57 njalo eminyakeni eyishumi.” Nokho, lo magazini unezela ukuthi lokhu kwanda ngokuyinhloko kubangelwa izindlela zokuxhumana ezithuthukisiwe, kuyilapho inani eliphakeme labantu abafayo libangelwa ngokuyingxenye ukwanda kwemiphakathi ehlala ngasogwini.

EPacific Ocean kunama-tsunami amaningi kakhulu ngenxa yokuthi ivame ukugadlwa ukuzamazama komhlaba. Eqinisweni, “awupheli unyaka ingagadlanga i-tsunami ebhubhisayo ndawana-thile ePacific,” kusho incwadi ethile, ebonisa nokuthi “kule minyaka engu-50 edlule, amaphesenti angu-62 abo bonke abantu ababulawa yizizathu eziphathelene nokuzamazama komhlaba e-United States babulawa ama-tsunami.”

Ikhona Yini Indlela Yokuwabikezela?

Phakathi kuka-1948 no-1998, cishe amaphesenti angu-75 ezixwayiso zama-tsunami ezakhishwa eHawaii ayeyiphutha. Ngokuqondakalayo, umlando onjalo wenza abantu bangabe besanaka. Nokho, manje sekusetshenziswa isimiso esingcono sokuthungatha, esiklanywe ngobuchwepheshe besimanje. Ingxenye ebalulekile yalesi simiso sokuthungatha yi-bottom pressure recorder (BPR), efakwa ezinkulungwaneni zamamitha, ekujuleni kolwandle.

Lo mshini ozwelayo ukwazi ukulinganisa umehluko womfutho wamanzi njengoba kudlula i-tsunami—ngisho noma ingaba isentimitha nje elilodwa ukuphakama. Isebenzisa amaza omsindo, i-BPR ithumela ukwaziswa ebhokisini elikhethekile elintantayo, lona elidlulisela ukwaziswa esiphuphuthekini. Isiphuphutheki sona sidlulisela umyalezo esikhungweni sokuxwayisa ngama-tsunami. Ososayensi bayaqiniseka ukuthi lesi simiso sokuxwayisa esinembile siyonqanda ukuhlatshwa komkhosi oyiphutha.

Mhlawumbe izici ezibaluleke kakhulu zokuthuthukisa ukuphepha ukuqapha nokufundiswa komphakathi. Ngisho nesimiso esiphambili sokuxwayisa asisizi ngalutho uma abantu bengasishayi mkhuba. Ngakho uma uhlala endaweni esemgodini, ngasogwini ethandwa ngama-tsunami, bese iziphathimandla zendawo zixwayisa ngokusondela kwe-tsunami noma uzwa ukuzamazama komhlaba noma ubona ukuncipha kwamagagasi okungavamile, qiniseka ukuthi ufuna indawo ephakeme ngokushesha. Khumbula, olwandle, ama-tsunami angahamba ngesivinini sendiza futhi angahlasela indawo engasogwini ngesivinini esikhulu. Ngakho lapho ubona igagasi, mancane kakhulu amathuba okuba ulibalekele. Nokho, uma uhlangana ne-tsunami uphakathi olwandle ngesikebhe noma udoba, ungakhululeka—cishe inkomishi yakho yekhofi noma ingilazi yewayini esetafuleni ngeke iphazamiseke.

[Umbhalo waphansi]

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(Ukuze ubone ukuthi indaba ihlelwe kanjani, bheka encwadini)

Ngokuvamile ama-“tsunami” aphehlwa ukuzamazama komhlaba phansi ekujuleni kolwandle

UKUHLUKANA KONGQIMBA LOMHLABA

UKUPHEHLEKA KWAMANZI

UKUKHUPHUKA KWAWO

ISIKHUKHULA SAMANZI

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(Ukuze ubone ukuthi indaba ihlelwe kanjani, bheka encwadini)

Ubuchwepheshe obusha, obusebenzisa imishini yokuthungatha ekujuleni kolwandle, buzama ukubikezela ama-“tsunami”

UMYALEZO OTHOLWA YISIPHUPHUTHEKI

IBHOKISI ELINTANTAYO

UMSHINI WOKUTHUNGATHA UMSINDO EMANZINI

IHANGE

UMSINDO OHAMBA EMANZINI

UMSHINI OTHUNGATHA AMA-TSUNAMI

amamitha angu-5 000

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Karen Birchfield/NOAA/Pacific Marine Environmental Laboratory

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Igagasi elinomfutho ladabula leli sondo leloli ngebhodi

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U.S. Geological Survey

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Indlu yesibani yaseScotch Cap e-Alaska ngaphambi kokuhlasela kwe-“tsunami” ngo-1946 (ngakwesobunxele)

Ukubhujiswa kwayo ngokuphelele kamuva (ngenhla)

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U.S. Coast Guard photo

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U.S. Department of the Interior