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Sosiale wetenskappe

Graad 7

Natuurgevare

Module 2

Tropiese siklone

1. Tropiese Siklone

  • Die voorkoms en ontstaan van tropiese siklone

Geen weerverskynsel is meer skrikwekkend en vernietigend as ‘n tropiese storm nie. In Amerika word dit orkane genoem, in Asië tifone, in Suid-Afrika tropiese siklone en in Australië Willie-willies.

Kenmerke van tropiese siklone

Hulle ontwikkel oor die warm, tropiese oseane naby die ewenaar. Die warm, tropiese seewater verhit die lug wat daarop rus tot temperature van ±27°C. Die hoë verdamping maak die lug ook baie vogtig. Die hoofkenmerk van die tropiese oostewinde is dus dat hulle warm en vogtig is. Dit veroorsaak dat die lug oor die oseane vinnig opstyg en ‘n intense laagdruk ontstaan. Die konveksiestrome begin in ‘n spiraal draai en die spoed daarvan neem toe. Verdere styging, kondensasie en die vorming van cumulus en cumulonimbuswolke ontstaan. Die wenteling van die aarde om sy eie as laat die wolkmassas sirkel om ‘n reusagtige, wentelende storm te vorm.

In die middel van hierdie sikloonsentrum is daar ‘n oog van kalm, wolklose weer wat sowat 35 – 50 km breed kan wees. Lugdruklesings hier is onder 1 000 hPa. Direk om die oog woed stormwinde van 120 – 280 km/h. Stormweer kan tot 200 km vanaf die oog voorkom en kan vir ‘n paar uur of selfs dae lank duur. Hulle beweeg stadig vorentoe (15 – 20 km/h) en begin afneem in geweld sodra dit landoppervlak of koeler water bereik. Geweldige verwoesting, stortreën en vloedgolwe kom egter vir etlike dae aan kusgebiede van lande voor.

Siklone het voorheen as gevolg van hulle wispelturigheid vrouename gekry om hulle uit te ken. Deesdae kan ‘n mansnaam ook gebruik word, soos die hewige tropiese sikloon “Hugo” wat in 1989 die ooskus van Amerika getref het.

Dit word op ‘n weerkaart aangedui deur ronde isobare wat naby mekaar geleë is om die oog. Die oog word ook met die simbool “

“ voorgestel.

Sinoptiese weerkaart

1.2 Die uitwerking (gevolge) van tropiese siklone op mense se lewens en hul sosio-ekonomiese aktiwiteite

Dit gebeur nie dikwels dat Suid-Afrika die volle geweld van ‘n tropiese sikloon ervaar nie. Wanneer dit wel voorkom, saai dit net soveel verwoesting as in ander wêrelddele.

Die grootste sikloon wat die kus van Suid-Afrika nog getref het, was die tropiese sikloon Demoina. Op 25 Januarie 1984 het Demoina naby Maputo na die binneland geswaai. Die volgende twee dae het dit hewige storms, sterk winde en baie reën oor Suid-Afrika veroorsaak. Soveel soos 540 mm is in 24 uur aangeteken. Riviere in Noord-Natal het oorstroom. Dorpies naby riviere is heeltemal vernietig, brûe het weggespoel en gewasse langs die riviere is verwoes. Skade aan suikerplantasies is beraam op R150 000 000. Minstens 200 mense het gesterf. Reddingspogings is belemmer omdat meeste brûe en paaie weggespoel het. Stormsterkwinde het dit gevaarlik gemaak om helikopters te gebruik. Daar is selfs lyke en krokodille see-in gespoel. Siektes wat deur die water versprei is en hongersnood het die sterftesyfers verder laat styg.

Aktiwiteit 1:

Om oor die uitwerking van tropiese siklone navorsing te doen

[lu 2.1]

Maak ‘n lys van alle gevolge van tropiese siklone nadat jy meegaande inligting oor Demoina gelees het. Gaan soek ook in koerante en ander bronne na artikels oor tropiese siklone en vul jou lys aan.

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Source:  OpenStax, Aardrykskunde graad 7. OpenStax CNX. Sep 09, 2009 Download for free at http://cnx.org/content/col11020/1.1
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