45

VULKANIZAM

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Razumijevanje sustava vulkana

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Vulkanske stijene

Glavna razlika između intruzivnih i vulkanskih stijena je struktura stijene koja odražava brzinu hlađenja magme.

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46

Materijal izbačen iz vulkana

Nevolatilni materijal i volatilni materijal

Nevolatilni materijal

• Lava

• Tefra

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Tipovi lave

"aa"

"pahoehoe"

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Kim Heacox/DRX

Pahoehoe lava

Aa lava

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47

Tefra

• piroklastični tokovi

• padanje iz zraka

• tečenje vulkanskog mulja (lahari)

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Piroklastični tokovi

• mješavine vrućih plinova, pepela i stijena

• formiraju: vrlo vruće i guste tokove

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Podmorske (submarinske)

erupcije

• pillow (jastučasti) bazalt

• freatičke eksplozije

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48

Eruptivni stilovi i formiranje

kopna

• vulkani u obliku štita

• stratovulkani

• dome i konusi

• pukotinske erupcije

• podmorske erupcije

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Vulkani u obliku štita

• tokovi lave niskog viskoziteta– magma niskog sadržaja silicija

– bazalt– Pahoehoe

– Aa

• blage padine - između 20 i 100

stupnjeva

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Vulkan u obliku štita

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49

Konusni vulkani

• izgrađeni jedino od piroklastičnih stijena

• strme padine

• relativno malih dimenzija

• kratko trajanje vulkanske aktivnosti

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Konusni vulkan

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Vulkanske dome

• formiraju se iznad vulkanskog otvora

• viskozna lava

• ne teče

• udružene s vrlo snažnim erupcijama

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50

Lava dome

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Stratovulkani

• izmjena piroklastičnih slojeva i tokova lave

• padine vulkana umjereno strme

• uglavnom andezitna lava

• distribucija

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Stratovulkan

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51

Kaldera

• depresija na vrhu vulkana

• unutar kaldere može biti i mlađih doma

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Razvoj kaldere

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Pukotinske erupcije

Nastaju kada niskoviskozna lava

izlazi iz pukotina u Zemlji u

dužini nekoliko desetaka

kilometara

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52

Pukotinska erupcija formira platoe od lave

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Tokovi lave

• mafitna lava

• javlja se u pukotinskim tokovima

• kolumnarni oblici

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Tećenje vulkanskog mulja (lahari)

• mješavina vode i piroklastičnog materijala kao gusta žitka masa slična tekućem betonu

• brzina kretanja i do 100 km/h

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53

Ostali materijali izbačeni iz vulkana

Volatilni materijal

• vodena para

• ugljikov dioksid

• sumporovodik

• mnogi drugi sadržaji

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Tektonski položaj vulkana

• konvergentne granice ploča

• divergentne granice ploča

• unutar ploča iznad "vrućih točki"

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Svjetski aktivni vulkani

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54

Vulkanizam i tektonika ploča

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Utjecaj vulkana na čovjeka

• izgradnja Havaja

• geotermalna energija

• utjecaj na klimu

• vulkanske katastrofe

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Vrste vulkanskog hazarda

• tokovi lave: Hawaii, 1998.

• plin: jezero Nyos (Cameroon), 1984.– 1700 poginulih

• padanje pepela: Mt. Pinatubo, 1991.

• piroklastični tokovi: Mt. Pelee, 1902.– 28000 poginulih

• lahari: Nevado del Ruiz, 1985.– 23000 poginulih

• tsunami: Krakatao, 1883.– 36417 poginulih

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