volc. nasci report

8/2/2019 Volc. Nasci Report

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About 500 active volcanoes are known on Earth,not counting those that lie beneath the sea.Volcanoes are not randomly distributed over the

Earth's surface. Most are concentrated on theedges of continents, along island chains, orbeneath the sea forming long mountain ranges.More than half of the world's active volcanoes

above sea level encircle the Pacific Ocean toform thecircum-Pacific "Ring of Fire".
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Volcanic eruptions occur only in certain places and do not occur randomly. That's becausethe Earth's outermost shell -- the lithosphere-- is broken into a series of slabs known as

lithosphericor tectonic plates. There are 16 major plates.


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How are they formed?

Volcanoes are generally found where tectonic plates arepulled apart or come together. Because of the faults andtension in Earths crust magma is able to pressure itsway out to the surface forming a volcano.

The structure and behavior of volcanoes depends on anumber of factors. Some volcanoes have rugged peaksformed by lava domes rather than a summit crater,whereas others present landscape features such asmassive plateaus. Vents that issue volcanic material(lava, which is what magma is called once it has escapedto the surface, and ash) and gases (mainly steam andgases) can be located anywhere on the landform.


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What are the parts of aVolcano?

1. VENT- the vent is the

opening from

which lavaflows.

- Dust, ash, and

rock particlescan also be

thrown out of

the vent!


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2. Crater

-the top of thevolcano.

- It is a funnel

shaped pit.-It is formedwhen the

materialexplodes outof the vent!


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3. Volcanic cone

- is the pile oflava, dust,ashes, and rock

around thevent.- It can be

found indifferentshapes!


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Types of Volcanoes

There are 3 types ofVolcanoes:

Shield

Cinder ConeComposite

They areclassified by

how they form.


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Shield Volcano

Is wide andsomewhat flat.

It forms from a quieteruption.

Lava flows outquietly and for greatdistances.


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Basaltic lava builds up in flat layers with few

pyroclastic material (particles ejected by

escaping gases)

Gently sloping sides

Ex: Hawaiian Islands (Mauna Loa)


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Low-Angle View of Mauna Loa

Source:Photograph courtesy of USGS Photo Library, Denver, CO.

S i i f ii


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Satellite View of Hawaii

Source: Photograph courtesy of USGS Photo Library, Denver, CO.


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Cinder Cone Volcano Built from ejected

lava fragments

Has tall, very steep

sides.

Has explosiveeruptions.

This eruptionproduces a lot ofcinder and ash.


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Granitic lava thrown high intothe air

Lava cools into different sizesof volcanic material calledtephra

Steep-sided, loose slopes
http://lava.nationalgeographic.com/pod/pictures/sm_wallpaper/NGM1993_01Earth1LoRt.jpg


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P i t V l E ti
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Paricutn Volcano Erupting


P i t Sh i F f
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Paricutn Showing Form of

Cinder Cones

Source: Photograph by K. Segerstrom, courtesy of USGS Photo Library, Denver, CO.


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Composite Volcano(Strato volcano)

Consists of alternatinglayers of lava flowsand pyroclastic

materials. Form from explosive

eruptions.

Produce a lot of lavaand ash.

Is small, with steepsides.
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A mix of the other two types

Quiet or violent Basaltic or granitic

Steep or gentle slopes

Layered or tephra
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Dome Formation Mount St
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Dome Formation, Mount St.

Helens


Composite Volcano in
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Composite Volcano in

the Aleutian Islands

Source: Photograph by R.E. Wilcox, USGS Photo Library, Denver, CO.


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Calderas

-volcanoes havingunusually largecaters

-formed if thesummits ofvolcanoes collapse

into the partiallyimplied magmachamber
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Shield volcano Stratovolcano

Lake Toba caldera Volcanic fissure
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o Volcanoes are continually lowered byerosion and mass wasting.

o After erosion, the more resistant rock thatoccupies the pipe may remain even if mostparts are gone ------ volcanic neck
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Volcanic Neck

A volcanic neck is the

remnant of an ancient volcano

If a volcano stops erupting,it stops growing

If eruptions cease, thevolcano will be subjected toweathering and erosion andwill ultimately be worn down

The volcanic neck representsthe innermost portion of aneroding volcano
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Igneous intrusions are formed when molten magmadeep in the earth forces its way up through coolerrock. If the cooled magma cuts across layers ofpreexisting rock, it is known as a dike (or dyke).

Dikes can form in rings or in long vertical ridges.Cone sheets are thin dikes that form in the shape

of an inverted cone. If the magma settles parallelto preexisting rock, it is known as a sill. Often,erosion will wear away preexisting rock, exposing anescarpment, or a dome-shaped laccolith.
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Theory of Plate Tectonics- includes the idea that the lithosphere

consists of as many 20-rigid plates

Formation of Bicol chain of seven volcanoes

- Mt. Labo in Camarines Norte, Ms. Isarogand Iriga in Camarines Sur, Mts. Malinao and

Masaraga in Albay, and Mts. Bacon and Juban inSorsogon --- as well as the presence of geothermalfields in Tiwi, Albay, and Manito-Bacon, Sorsogon.
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The earths crust is divided into 20 rigidplates 50 to 160 km thick. These

plates move slowly and slide over a hotsemi-plastic layer of magma called theastenosphere.

When the plunging edge of the Philippineplate hits the hot clastic astenosphere,it melts. At the same time, the hotmagma rises, heats and reacts with the

lithosphere. Then it passes through thevertical cracks or crevices at thebottom of the eastern portion of Chinaplate.
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The subduction zone is just below thesouthwestern tip of the Bicol peninsula.

The upwelling magma or liquid rock goesup with tremendous pressure towardsthe surface of Bicolandia throughseveral fissures, initiating the formationof a chain of volcanoes. As a result ofthis, the conduits of Mayon and Bulusanare still lightly plugged, such that

pressurized lavas can be found in theircraters, causing volcanic eruptions fromtime to time.

Pl t t t i A th h i h lti
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Plate tectonics: Asthenosphere is where melting occurs

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