Volcanic Activity

Volcan c Act v ty

Classification of Volcanic Activity

1. Active- a volcano that is erupting or has repeatedly erupted in

a short period of time2. Dormant- a volcano that has not

erupted for a considerable length of time

3. Extinct-a volcano that shows no any evidence of erupting again

Classification of Volcanic Eruption

Type of eruption

MeaningReaction of

heat to water or ice

Magmatic Eruption

Eruption-produces juvenile clasts

during explosive decompression

from gas release

Thermal Expansion

Phreatomagmatic eruption

characterized by an explosive

water-magma interaction

through which large amounts of

steam and magmatic gases

are released

Thermal Contraction

Types of Volcanic Eruption

Specific type

UnificationDistinguished

featuresDisplayed

in/byHawaiian Magmatic Generally basaltic

Low level eruption Effusive eruption/fire fountain Column generally less than 500

m Associated with a hotspot Fluid lava flows Result in vast gentle volcanoes

Kilauea, Hawaii

Mauna Loa volcano in 1950

Lava lake Magmatic • Rare cases• Very fluid lava• Weak pyroclastic production

Mauna Ulu, Lava Lake

Erta Ale, Ethiopia

Strombolian Magmatic Basaltic magma More viscous than Hawaiian Intermittent explosions No sustained column Ejecta to heights of a few

hundred meters Minutes of pause between

bursts

Stromboli, Sicily

Paricutin 1943-1952

Mt. Erebus, Antartica

Types of Volcanic Eruption

Specific type

UnificationDistinguished

featuresDisplayed

in/byVulcanian Magmatic Similar to hydrovolcanic

activity Begins with violent noisy

explosion Ejects new lava fragment that

do not take on a rounded shape during their flight through the air

Highly viscous fragmented magma

Clouds rise to 10-20 km Wide dispersal of tephra Can last, with long intervals of

repose, for several millenia

Vulcano, Sicily

Sakurajima in Japan (ongoing) and Irazu in Costa Rica (1965)

Plinian Magmatic Rare events (2-3 in century) Most explosive and powerful Highly evolved magma with

abundant pumice Statospheric eruption columns Huge volumes and large mass

flux

Vesuvius, 79 CE

Mt. Pinatubo 1991

Types of Volcanic EruptionSpecific

typeUnification Distinguished features

Displayed in/by

Subplinian Magmatic High eruptive plumes up to 30 km

Eruption happens after long years of dormancy

Sustained column Generally dacite to rhyolite

composition Continuous sheet of tephra Pumice is common Less fragmented than Vulcanian

products Discrete explosions lasting

seconds to few minutes

Vesuvius, 1822

Phreato-plinian

Phreato-magmatic

No historic eruptions of this type High eruptive column Extremely fine tephra Wide dispersal of deposit

none

Types of Volcanic EruptionSpecific

typeUnification Distinguished features

Displayed in/by

Surtseyan/ Hydro-volcanic

Phreato-magmatic

Rapid small explosion Viscous, basaltic Column less than 500 m Associated with surge clouds Highly fragmented material Commonly within a standing

water body

Surtsey, Iceland

Fire Island, Alaska, USA 1796

Taal Volcano, Batangas, Philippines (last eruption was in 1977)

Subglacial

Phreato-magmatic

No eruptive column. Some ash on the surface of ice sheets

Only surface effect is a ‘’sag’’ in the glacier

Melted ice, fragmented lava and water flood out

Iceland

Process involved in Volcanic Eruption

Volcanic Process- refers to the eruptive and noneruptive activities

that take a place on a volcano

Volcanic activities results if:

1. Confining pressure decreases as a result of decompression from the magma rising from a higher pressure point to a lower pressure point

2. Vapor pressure increases because the magma cools which initiates a crystallization process that enriches the magma content.

Volcanic Materials Brief Description Illustration

Andesite a dark grey volcanic rock

Basalt

a dense dark grey fine-grained igneous

rock that is composed chiefly of plagioclase

feldspar and pyroxene

Dacitea grey volcanic rock

containing plagioclase and quartz and other crystalline minerals

Diorite a granular crystalline intrusive rock

Different volcanic materials


Gabbro one of a family of granular intrusive rocks

Granodioritean intrusive igneous rock

similar to granite, but containing more plagioclase

than potassium feldspar

Obsidianacid or granitic glass formed by the rapid cooling of lava

without crystallization; usually dark, but transparent

in thin pieces

Pegmatitea form of igneous rock consisting of extremely

coarse granite resulting from the crystallization of magma

rich in rare elements



Peridotitea dark coarse-grained

igneous rock consisting principally

of olivine

Plutonic

igneous rock that has solidified beneath the

earth's surface; granite or diorite or

gabbro

Pyroxenite

A heavy, dark igneous rock consisting mostly of pyroxene minerals with smaller amounts

of olivine and hornblende

Scoriathe scum formed by

oxidation at the surface of molten

metals



Rhyolite very acid volcanic rock

Tuffhard volcanic rock

composed of compacted volcanic

ash

Volcanic Gases

Volcanoes emit gases during eruptions. Even when a volcano is not erupting,

cracks in the ground allow gases to reach the surface

through small openings called fumaroles


Thank you for listening!

Prepared By: Julius Cagampang

Education

Volcanic Activity