4b- Igneous Activity - b

7/30/2019 4b- Igneous Activity - b

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IGNEOUS ACTIVITY

( IGNE = FIRE )


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. ,it loses some of its dissolved gasses and liquids, becoming LAVA

The main fluids escaping

magma are gasses, which

H2O, H2S, SO2 , N2etc )and very hot water


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Lava and pyroclastic fragments (volcanic ash, tephra) are thrown out

during a volcanic eruption.


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AGRIDAG volcano is surrounded by early erupted lavas and tephra.


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Eru tion t es and related volcano t es:

Dome, cinder cone, maar, lava spatter cone

Central Composite volcano (Strato-volcano)

eruption

Shield volcano

Fissure eruption Plateau basalts


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-

Mostly intermediate magma types produce this kind of volcano


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Ver felsic slow movin lava cannot roduce a volcanic cone

but develops a dome just below the surface.

Dome

Country rockPipe

Magma chamber


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Richat structure is a DOME in North Africa. Its diameter is about 50km. The la ers of countr rock have been ushed u wards to form

ring shaped hills (Photo taken from a satellite).

m


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Cinder cone : Made u onl of solid lava fra ments and rock fra ments


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Maar is a low relief volcanic crater, made b ex losion of

magma when it meets water near the surface.


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Sometimes Maar may be filled with water, forming a shallow lake


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Crater is the depression at the top of the volcanic cone. Cratersize ma be a few hundred meters in diameter. It is formed b

to the explosive force of volcanic eruption.


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a era s muc argerthan crater. Calderamay be several km or

in diameter.

Caldera is formed bythe collapse of magmachamber below, when itbecomes empty aftermany erup ons.

Magma chamber


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Caldera


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Sometimes caldera occurs at sea level or even at the sea floor.


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Sometmes very power u eruptons can parta y estroy ear ercraters and calderas.


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, .

Because lava flows so easily, it cannot accumulate to form a cone


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Plateau basalts form due to eru tion of lava throu h fissures.

Mafic lava mainly erupts following fractures (fissures) in theEarths crust, producing flat plateaus made of basalt layers.


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ava ypes are c ass e y orgna magma compos on, aswell as by the final texture. Because of rapid cooling conditions,these rocks are either fine grained or glassy.

Lava types and related volcanic rocks

IntermediateComposition

PUMICE SCORIAVesicular

RHYOLITE ANDESITE BASALT

(ropy, blocky, pillow)

Rocky

L

AT

e s c a c

Lapilli (1 mm 10 mm)Mediu

Volcanic breccia, volcanic bomb, block, clastCoarsePyroclastic

(ash)T

OBSIDIAN, FELSITE PALAGONITEGlassy

A

E

X

T

U

Glowing avalanche, welded tuff (ignimbrite)HotFragmental

Tuff, Tuffite (layered tuff) (< 1 mm)Fine

mP

H

R

A

R

E

Lahar, volcanic mudflowCold

fluids

,

volatiles (gasses) (H2O, CO2, H2S, SO2,...... etc) and hot water.


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Rocky lava textures

PLAN PLAN

Ropy lava ( mafic) Blocky lava ( felsic)

Oceanic crust

Volcanic bomb

Pillow lava ( mafic )


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Rocky lava textures

PLAN PLAN

Ropy lava ( mafic) Blocky lava ( felsic)

Volcanic bomb

Oceanic crust

Pillow lava ( mafic )


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Vesicular lava textures

Scoria structure : Vacuolesare formed due to gasbubbles, which are generally

s herical, indicatin no flow

Flow direction

Pumice structure : Vacuoles are elongated along flow direction.


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ava ypes are c ass e y orgna magma compos on, aswell as by the final texture. Because of rapid cooling conditions,these rocks are either fine grained or glassy.

Lava types and related volcanic rocks

IntermediateComposition

PUMICE SCORIAVesicular

RHYOLITE ANDESITE BASALT

(ropy, blocky, pillow)

Rocky

L

AT

e s c a c

Lapilli (1 mm 10 mm)Mediu

Volcanic breccia, volcanic bomb, block, clastCoarsePyroclastic

(ash)T

OBSIDIAN, FELSITE PALAGONITEGlassy

A

E

X

T

U

Glowing avalanche, welded tuff (ignimbrite)HotFragmental

Tuff, Tuffite (layered tuff) (< 1 mm)Fine

mP

H

R

A

R

E

Lahar, volcanic mudflowCold

fluids

,

volatiles (gasses) (H2O, CO2, H2S, SO2,...... etc) and hot water.


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Wind direction

Tephra ( ash )

Lava

Pyroclastics Tuffite Tuff


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Fragmental flow texture, due to escaping hot gasses

Glowing avalancheGlowing avalanche

Lava

Welded tuff ( Ignimbrite )

Lava

Welded tuff ( Ignimbrite )


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Flow due to cold fluids, such as water from melting snow and ice.

Tuff accumulation

LAHAR is similar to mudflow; however, particles are mostlyvolcanic tephra (pyroclastic materials)


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.

reaches the surface. This can happen above land surface, or atthe bottom of sea or ocean. When all the energy accumulated inthe ma ma chamber is used u volcano sto s eru tion.

If a volcano temporarily stops erupting, it is called a Dormant

volcano. However, all Active volcanoes eventually becomeExtinct.

When a volcano stops erupting, weathering, erosion and

Extinct, such processes can completely remove the volcano andits products from that area.

Relatively resistant igneous rocks may be left behind as volcanicnecks, dike walls and flat mesa hills.


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Erosion of land surface after volcanoes become dormant or even extinct


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11. Volcanoes on the Earth surface :

Lavas of volcanoes are mmostly andesites

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4b- Igneous Activity - b