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Sosiale wetenskappe

Graad 7

Natuurgevare

Module 4

Vulkane

1. Vulkane

1.1 Die voorkoms en oorsake van vulkane.

Die gesmelte rots onder die aarde word magna genoem. Wanneer dit op die aardoppervlakte uitvloei, word dit lawa genoem. Oor die presiese oorsake van vulkaniese uitbarstings dink die geleerde mense egter nog nie eenders nie. Niemand kan in die hart van die aarde gaan kyk wat aangaan nie.

Ons weet wel dat die aardkors so swaar op die magma van die mantel rus, dat hierdie vloeibare rots byna soos ‘n pitseer se pit deur ‘n swak plek in die aardkors na boontoe gedruk word. Hierdie gesteentes het ‘n temperatuur van tussen 800ºC en 1 500º C.

As jy ‘n gaskoeldrankblikkie vat en jy skud dit, sal die koeldrank uitspuit as jy dit oopmaak. ‘n Vulkaan werk presies dieselfde – gesmelte rots bars deur die swak plekke in die aardkors en die lawa, rotsblokke en as word die lug ingeskiet.

Die lawa stol en vorm nuwe rotse wat ons stollingsgesteentes noem.

Party vulkane se lawa is baie loperig en vloei ver oor die oppervlakte voordat dit stol. Dun plate stollingsgesteentes word so gevorm. Ander vulkane bou weer ‘n koepel op omdat die lawa taaier is en dus nie ver kan vloei nie.

Soorte vulkane

Met ‘n geweldige uitbarsting kan die koepel se kop heeltemal weggeskiet word en ‘n oop gat ontstaan wat ‘n kaldera genoem word.

Vandag is daar maar ± 450 aktiewe vulkane op die aarde. Hulle hou gelukkig nie altyd aan met uitbars nie en word dan rustende of passiewe vulkane genoem.

Waar kom die meeste vulkane voor?

Daar is sowat 500 vulkane in die wêreld en hulle kom net op sekere plekke voor. Hierdie plekke lê op die rand van die groot plate van die aardkors. As hierdie plate beweeg, ontstaan vulkaniese uitbarstings en aardbewings.

Die verspreiding van die vernaamste vulkaan- en aardbewinggebiede van die aarde

Watter vulkane het die meeste verwoesting aangerig ?

Die vulkaan wat die ergste verwoesting nog aangerig het, is Krakatoa in Indonesië. Dit het in 1883 uitgebars en meer as 36 000 mense het gesterf. Die knal is 5 000 km ver gehoor en die lugbesoedeling het vir jare nog koperkleurige sonsondergange op die aarde veroorsaak.

Nog ‘n bekende voorbeeld van ‘n verwoestende vulkaan is die uitbarsting van berg Vesuvius, wat in 79 n.C. die stad Pompeji in die Baai van Napels heeltemal onder vulkaniese rotse en as begrawe het.

2. Die uitwerking (gevolge) van vulkane op mense se lewens en hul sosio-ekonomiese aktiwiteite

In die swart hemel van die nag vonkel duisende liggies. Op ‘n afstand lyk dit na ‘n ontsaglike vuurwerkvertoning soos die vulkaan in gloeiende rotse en strome van vuur ontplof. Rotse en as word die lug in geskiet en veroorsaak lugbesoedeling.

Oor die rand van die krater kruip die rivier van rooi, rokende lawa – warm bloed van die lewende aarde, soos iemand dit al treffend beskryf het.

Kilometers ver vloei dit miskien deur vrugbare valleie, verteer dit elke grashalm en selfs bome op sy pad. Maar ook huise verkrummel en stede word onder die voortstuwende gloed begrawe. Mense wat dit oorleef, vlug van die hange af ; warm as reën op hulle neer. Lewensverliese kom ook voor omdat mense versmoor as gevolg van die verstikkende swaelgasse en asreën wat ontstaan.

Questions & Answers

Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
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Jyoti Reply
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Crow Reply
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RAW Reply
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Damian
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Professor
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Professor
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Brian Reply
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Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
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LITNING Reply
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LITNING Reply
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LITNING Reply
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LITNING
scanning tunneling microscope
Sahil
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Santosh
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Rafiq
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what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
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Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
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Renato
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Kyle
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Adin
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Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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research.net
kanaga
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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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