Volcanoes

Volcanos world

Dr. Masdouq Al Dr. Masdouq Al --TajTaj

Faculty of Natural Resources and EnvironmentThe Hashemite University

Environmental GeologyEnvironmental Geology Environmental GeologyEnvironmental Geology Environmental GeologyEnvironmental Geology Environmental GeologyEnvironmental Geology Environmental GeologyEnvironmental Geology

VolcanoVolcano

lavalava

Pyroclastic FlowPyroclastic Flow

MagmaMagma

PyroclasticsPyroclastics

CraterCrater

a cone-shaped mountain formed from lava

and /or pyroclastic

A body of molten rocks found at depth,

including any dissolved

gases & crystals.

A body of molten rocks found at depth,

including any dissolved gases & crystals

the volcanic rocks ejected during an eruption.

Pyroclastics include ash, bombs and blocks.

a highly heated mixture, largely of ash and

pumice fragments, traveling down the flanks of

a volcano or a long the surface of the ground

The depression at the summit of a volcano.




The Nature of Volcanic EruptionsThe Nature of Volcanic Eruptions

What determines, whether a volcano extrudes magma violently or gently?What determines, whether a volcano extrudes magma violently or gently?

1. Magma’s composition.( SiO2 content).

2. Magma's temperature.

3. The amount of dissolved gasses it contains.

The more The more viscous the viscous the

magma, magma, the greater the greater

its its resistance resistance

to flowto flow . . All of above points affect magma viscosity

table




Factor effecting viscosityFactor effecting viscosity

•Temperature. •SiO2 content; The more the SiO2 content, the greater viscosity .

Materials Extruded During An EruptionMaterials Extruded During An Eruption

1. Lava flow.2. Gases.3. Pyroclastic materials.




Lava FlowLava Flow

Basaltic: example: as in Hawaii Islands (Mauna Loa,

the largest on the Earth and Kilauea)

- Flow rapidly 10-300 m/hr may reaches 30 km/hr.

- Travel about 150 km before congeal (consolidate).




Basaltic flows in Hawaii formBasaltic flows in Hawaii form

1. pahoehoe flows: A lava flow with smooth- to- ropy surface. It resembles the twisting braids in ropes.

2.aa flows: A lava flow that has a jagged blocky surface.

http://www.decadevolcano.net/photos/europe/etna/2004/etna_46003.jpg










Lava tubesLava tubes

conduit that the molten lava continued to move through it.

Pillow lavaPillow lava

basaltic lava that congeals under water environment and develops a structure that resembles a pile of pillows.

1. Andesitic: intermediate viscosity. 2.Rhyolitic: This is too slowing, thicker and

more viscous than andesitic or basaltic




Gases Gases

Magma contains variable amount of dissolved gases held in the molten rock by confining pressure.

These gases are:70 % = water vapour.15% CO2. 5% = N2. 5% = S.and amount of Cl2,H2,Ar.The gas content is important in widening the volcanic vent and the cracks by the expansion of the gases to hundred or thousand times.




Pyroclastic materialsPyroclastic materials

Pyroclastic material is any ejected lava fragments of ash, dust, glass fragments, ….. that range in size from microns to large pieces of metric size.

Ex

amp

les

Ex

amp

les

Ash: rise in the atmosphere that cause darkness and the drop of temperature in the atmosphere.Tuff: A rock formed from fine-grained pyroclastic particles

)ash and dust.(Pumice: light, glassy, highly vesicular, it is as forth like lava.Lapilli: size of walnut = little stone.Cinder: pea-size= contain voids resulting from escaped gases.

Blocks: large grainBomb: A streamlined Pyroclastic fragment ejected from a volcano while molten.

table




Volcanoes And Volcanic Eruption Volcanoes And Volcanic Eruption

Based On Their Eruptive Patterns & Characteristic Form, Three Groups of Volcanoes Are Recognize:

1. Shield volcanoes.2. Cinder cones.3. Composite cones (stratovolcano).

http://www.decadevolcano.net/photos/etna0701_1.htm




Shield volcanoesShield volcanoes

1. Broad, gently sloping volcano built from fluid basaltic flow .2. Have small percentage of pyroclastic material.3. Ex: Mauna Loa, the largest volcano on the earth surface, is one of the

five shield volcanoes that together make up the island of Hawaii. Its elevation reaches 9170 m (5000 m above ocean floor and 4170 m above water surface).




Cinder conesCinder cones 1.Build from ejected pyroclastic materials.

2.It has a high angle (30-40 degree). Cinder cones are small, usually less than 300 m in height.

ExEx: Paricutin (west Mexico city) Cinder cones .




Composite coneComposite cone

Composed of alternatives of lava flows and pyroclastics. - Steep near the crater & more gentle a way. - Andesitic lava (intermediate). - Encircle the Pacific Ocean (Ring Of FireRing Of Fire). Ex: Mt. Fujiyama (Japan), Vesuvius (Italy, extruded violently in A.D 79), Mount Mayon (Philippines), Cascade Range in the northwestern part of USA. It includes (Mt. St. Helens, Mt. Rainier and Mt. Shasta).




nuee ardentenuee ardente =glowing avalanche: it is deadly pyroclastic flow that occur when hot gases infused with incandescent ash are ejected, this fiery cloud race down the volcano flank and travel a bout 200km/hr, and reach a bout 100 km away from the source. (in Pompeii (Italy) during 3 days, 2000 person were killed)

LaharLahar: Ash + rain, which moves rapidly (about 30 km/hr) and carries the materials in its way.

Composite coneComposite cone







VolcanicVolcanic LandformsLandforms

The most obvious volcanic landform is a a conecone , but there are other landforms:

1.Crater and caldera:

Caldera is a large crater (must be >1 km in diameter)caused by collapse or ejection of the summit

of a volcano.





2.Volcanic Neck: An isolated, steep-sided, erosional remnant

consisting of lava that once occupied the vent of the volcano.

3- Vent & Pipes : Vent: conduit connects the magma chauper to a volcanic crater. Pipe: a vertical conduit reaches a bout 200-km or more throw which magmatic materials have passed. So it is consider as a window on the upper mantle (Asthenosphere), mostly the magma of ultramafic type. - Ex: diamond-bearing pipes of South Africa.





4- Fissure Eruptions and Lava Plateaus:

Fissure eruption: eruption where basaltic lava is extruded via fractures or crack in the earth

crust.The eruvative material cover an extensive area to

thickness of hundreds of meters, form Flood Basalt.

Plateaus: flat topography result from repeated eruptive phases of lava, it may reach 2-3 km in thickness and composed from flood basalt.





5- Pyroclastic flow:

Rich in SiO2, mainly of ash and pumice fragments, when rest on the earth surface, it resembles lava flow.Ex: Yellowstone plateau, Wyoming, USA.


Technology

Volcanoes