Igneous Petrology Part 4

Volcano

is a naturally occurring landform where lava is erupted in the earth's surface

Volcano is a considered a MOUNTAIN only that magmatic chamber exist which erupts lava into the surface of the earth

DECOMPRESSION

Why do volcanoes erupt?

Volcanoes erupt because of density and pressure or simply due to DECOMPRESSION

Shield
Cinder Cone
Composite

What are the three types of volcanoes based on geomorphology?

Active
Inactive
Dormant

What are the three types of volcanoes based on activity?

Volcano types can be divided based on their GEOMORPHOLOGY, ACTIVITY and COMPOSITION

Shield Volcano

Gentle slope (15 degrees or less)
Resembles a Roman Shield lying on the ground
Successive Lava Flow
Quite Eruption (less viscous)

Cinder Cone Volcano

Steep Slope (30-40 degrees)
Relatively Small <300m height
Pyroclastic Flows
One time Big time Eruptions

Composite Volcano (Stratovolcano)

interlayered structure of tephra and lava flows

A tall coned shaped layered structure
Tephra and lava flows

In volcanology, Composite and stratovolcanoes are different in a way that:

Composite: has a dome in the middle
Stratovolcano: the dome is absent

Pacific Ring of Fire
Hot Spots
Spreading Centers
Subduction Zones

Distribution of Volcanoes

Volcanic Explosivity Index (VEI)

is based on a number of things that can be observed during an eruption.

Volcanic Explosivity Index (VEI)

measures the explosiveness of volcanic eruptions on a scale of 1 to 8

Strombolian Eruption

Short-lived and episodic eruptions with explosive outbursts of pasty lava

Hawaiian eruption

Calmest Eruption type characterized by effusive emission of fluid basalt lavas

"steady lava fountaining"

fire fountains
curtain of fire

Icelandic Eruption

Characterized by effusion of basaltic lava that flows from long, parallel fissures

Calmest of the calmest eruption
It only flows

Vulcanian Eruption

occurs in a series of discrete cannon-like explosions that are short-lived lasting for ONLY 2mins to FEW HOURS.

more explosive than Strombolian

Plinian Eruption

generate sustained eruptive columns reaching ~45km

Phreatomagmatic Eruption

generated by the interaction of MAGMA and Groundwater or Surface water

more explosive as the water is HEATED

Phreatic Eruption

a steam eruption without lava ejection
common precursor of volcanic activity
caused by groundwater flashing to steam as it is heated by magma

1815

A YEAR WITHOUT SUMMER due to Tambora Eruption

Mount Pinatubo Eruption

is a magmatic explosive eruption on June 12, 1991 forms enormous eruption columns of gas and ash above the volcano

Plinian Eruption

Mount Pinatubo Eruption is what type of eruption

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We have ____ active volcanoes and _____ potentially active volcanoes

Active Volcano

a volcano that had at least ONE eruption during the past 10,000 years

an active volcano might be erupting or dormant

Erupting Dormant

an active volcano might be ____ or ____

Inactive volcano

is an active volcano that is not erupting but supposed to erupt again

Extinct Volcano

A volcano that has not erupted for thousands of years and probably will not erupt again.

Mayon Volcano
Taal Volcano
Mt. Pinatubo
Mt. Kanlaon
Mt. Hibok-hibok
Mt. Bulusan
Mt. Musuan

Most Active volcanoes in the Philippines (7)

Volcanic Eruption

Sudden occurrence of a violent discharge of steam and volcanic materials

Magma Composition
Temperature
Volatiles/dissolve gasses

3 factors that affect the occurrence of volcanic eruption

Viscosity

the state of being thick, sticky, and semifluid in consistency, due to internal friction.

The greater the VISCOCITY the greater it's RESISTANCE to flow

Pyroclasts

ejected broken rock particles

Fragments of erupted rock

Pyroclasts

Fragments of volcanic material that is thrown out during explosive eruptions

Pyroclasts

which means "fiery fragments"

Airborne Tephra
Pyroclastic Flows

Pyroclasts may be ejected to the atmosphere as __________ or transported along earth's surface as ___________.

Lithic Pyroclasts Vitric Pyroclasts Crystal Pyroclasts

Material types in a PYROCLASTS

Lithic Pyroclasts

contain fragments such as basalt, andesite or other
rocks.

Vitric Pyroclasts

contains glassy fragments such as pumice and scoria

Crystal Pyroclasts

Contains Minerals
These are pyroclasts that contain Minerals

Pyroclast

An individual fragment ejected during volcanic eruption

Pyroclastic Rock

any rock consist of "unreworked" solid material of whatever size explosively or serially ejected from a volcanic vent

Pyroclastic Material

Any VOLCANIC MATERIAL that is ejected into the air. Composition can range from basaltic to rhyolitic

Blocks

are solid when ejected

Bomb

are liquid when ejected

Breadcrust Bomb

Formed if the outside of a bomb solidify during flight.

Lapilli

Rock fragments formed from ejected droplets of magma

Ash

usually glass but sometimes contain mineral fragments

Tuff

it is called consolidated ash

Juvenille magmatic clasts

range of vesicularity from highly vesicular pumice/scoria to variably vesicular blocks/bombs

Cognate Clasts

derived directly from magma involved in the volcanic activity

Accidental clasts

derived from older rocks that formed from vent walls or sept up from the ground

Explosive eruption

involves RAPID RELEASE and decompression of gas which results to SIMULTANEOUS fragmentation and ejection of magma

Explosive magmatic
Phreatomagmatic
Phreatic

3 types/style of explosive eruption

Pyroclastic Fall
Pyroclastic Flow
Pyroclastic Surge

Pyroclastics are dispersed by :

Pyroclastic Fall

mantle bedding with plane parallel and no
internal erosion, good sorting, juvenile clasts with angular to ragged shape (also known as tephra fall)

Pyroclastic Flow

Nonmantling beds, thickening into low lying areas, with some degree of rounding

Pyroclastic Surge

Landscape filling, ALL POOR

Pyroclastic processes

a process of fragmentation where explosive ejection and AERIAL DISPERSAL of pyroclasts (also called ejecta/tephra) of rock and magma from a volcanic vent; essential attribute is the presence of vitroclasts

Autoclastic processes

a process of fragmentation formed as a result of the breaking up of the cooler, crusted more rigid margin. Creates bloc-sized AUTOCLAST

Epiclastic processes

a process of fragmentation where EPICLASTS of a wide range of sizes are created by weathering and disintegration of volcanic rock

Mass Flow Transport

where group of clasts "move together" and interact

Traction Transport

Clasts are "entertained" in moving interstitial fluid and are FREE TO BEHAVE INDEPENDENTLY"

Suspension Transport

Clasts are "fully suspended" in interstitial fluids

Nuees Ardentes

hot avalanches in association with extrusion of lava dome

Pahoehoe lava

low viscous "runny" basaltic lava.
thin and quick. ropy looking, smooth surface, very hot temps. Low viscosity

Aa lava

thicker rough and slow moving lava , jagged blocks, cooler temps. high viscosity

Pyroclastic Cones

Steep sided conical features composed of tephra. (~30-35deg)

scoria cone

Steep sided coned formed by accumulation of ash lapilli bombs and blocks around a central vent resulting from cinder cones

Maar

Broad accumulation dome with a large central crater resulting from eruption through water-saturated ground.

Tuff Ring

Similar to maar but lacking central crater.

Tuff Cone

Steeper sided and smaller accumulation of volcanic debris than tuff ring. similar shape to scoria cone but layers deep inward near neck

Basaltes
L.Bassanites

Basalt came from the latin word _______ missed spelling of _________

Basalt came from the latin word BASALTES missed spelling of L. BASANITES which means very hard stone. Imported from ancient greek from BASANOS which means "touch stones" and originated in egyptian bauhun called "slate"

Basalt

a fine grained mafic igneous rock consisting of augite and calcic plagioclase

Augite

a variety of high Ca pyroxene

Calcic Plagioclase

with more anorthite than albite

Basalt

is a BASIC ROCK with SiO2 ranging from 45-52%

Restricted to rocks with total alkali content less than 5%

Tholeiitic
Alkaline
Calc-Alkaline

3 principal types of Basaltic Magmas

Tholeiitic Basalts

are basalts that are commonly found in mid-oceanic ridges (MOR) and intra-plate setting

Alkaline Basalts

are basalts that are commonly found in intra-plate setting

Calc-Alkaline Basalts

are basalts that are commonly found in Convergent Plate Boundaries

Harker Diagram

SiO2 vs other major Oxides
one of the most common variation diagram
by alfred harker (1909)

Olivine phyric basalt

Basalt containing olivine

Picrite

a basaltic rock that is visibly enriched with olivine crystals often as phenocryts

Ankaremite

basaltic rock rich in olivine and augite phenocrysts

Picrobasalts

having lower SiO2 content than
basalt (ultrabasic in composition), more olivine-rich
and contain little plagioclase

Basaltic Andesite

- have mafic mineral similar to
basalt but contain plagioclase of more sodic
composition (typically andesite)

Trachybasalts, basanites, and tephrites

usually contain recognizable alkali feldspar or feldpathoids

Boninite

a high-Mg form of basalt that is erupted generally in back-arc basins, distinguished by its low Titanium content and trace element composition

Mid-oceanic ridges basalts
ocean island basalts
large igneous provine/ oceanic plateaus and continental Flood basalts
intra-continental rift basalts
Subduction-related basalts
a. low k or island arc tholeiite arc basalt
b. high k arc basalts
c. basalt from back-arc basin
d. basalts from active continental margin

Mid-oceanic ridges basalt (MORB's)

MOR system >60,000 km in length
erupts basaltic lava at avg rate 3km3/year
Basalts erupted at MOR are olivine tholeiitic basalts mnaybe aphyric but more commonly contain phenocrysts of ol+chromite+pl+augite+plmost abundant

most distinctive aspect of MORB's is chemical composition ; LOW K2O

Hot Spot

localized source of magma supply

Peridotite

dominant rock type of the earth's upper mantle

Dunite

mostly olivine

Harzburgite

Olivine+ orthopyroxene

Wherlite

mostly olivine+clinopyroxene