Ch 3 Volcano & Extrusives

Volcano History • Named after Vulcan - Roman

God of Fire and Metalworking• Associated w/ gods or hell

1. Hawaiian - Pele

2. Greek – Hephaestus; son of Hera

3. Europe in the middle ages -

a. Gateway to hell

b. Prisons of the damned;

Noises were "screams of

tormented souls“

Volcano Distribution

2 major volcano belts1. Pacific Ring of

Fire

2. Mediterranean Belt

Magma vs. Lava

• Magma – liquid rock under the surface

• Lava – magma that reached the surface

• Magma described as Mafic, Felsic, or Intermediate

Mafic Magma• Less than 50% silicate

– Ex minerals: olivine, pyroxene, amphibole, biotite mica, and plagioclase feldspar.

– Ex rocks: basalt and gabbro.

• high magnesium, iron, and calcium• dark color• Dense• quiet eruptions• low viscosity

Felsic Magma• 65% silicates

• low in Mg, Fe, & Ca• Ex minerals: quartz, muscovite mica,

and orthoclase feldspar• Ex rock: granite

• light color

• less dense

• high viscosity

• explosive eruptions

Speed of Lava FlowBased on 3 traits

– Temperature• Hotter is faster, cooler

is slower

– Amount of Silicates• Low is faster, high is

slower

– Amount of dissolved gases

• High is faster, low is slower

3 Types of Volcanoes1. Shield Volcano

• mafic magma; basalt

• Common above hot spots

• Hawaiian Islands – Mauna Loa

• Large but not steep• Nonviolent and quiet

oozes; • low viscosity, runny

2 Types of Low Flow

• AA – surface cools while

flowing– Looks broken

• Pahoehoe– Surface stays fluid,

keeps flowing– Looks smooth and

ropy

2. Cinder Cone• Felsic magma; explosive• Small but steep; 33° • Build up of cinders (pumice,

scoria, pyroclastics, or tephra)

• Tend to pop up next to other volcanoes

3. Stratovolcano• Intermediate, mafic & felsic• large (1 - 10 km across)• Ka-boom then ooze• Explosive• Adnesite rock (intermediate) –

higher silica content • Sticky magma that plugs up til

breaking pt. (Zits on earth)• Creates pyroclastic material • Ex. Cascade Range, Dante’s

Peak, Mt. Fiji 

What comes out?• Pyroclastics – different sizes of

“fire broken” rock; cool fast– Ash (tuff): smallest– Pumice: volcanic glass; gas

bubbles– Scoria: cinder, basalt, iron rich;

gas bubbles– Lapilli (walnut-sized) – Volcanic bombs (basalt)

More Dangers• Pyroclastic flows

– (nuée ardente) – hot & fast

• Gases– CO2

– SO2 + water = sulfuric acid

• Lahars – Down hill mud flow– Snow & ice melt– Picks up debris– Local dangers

Other Volcanic “Things”Mafic Flows –

• Lava tubes

• Pillow basalt

• Columnar Jointing

• Fountains

Lava Domes – super volcanoes• all felsic

• high silicate

• high viscosicty

• very violent– Obsidian – cools

instantaneously; Newberry Crater Obsidian flows

– Caldera– Yellowstone National

Park

CalderasVolcanic peak disappears • Major explosion• Leaking magma to side• Collapse into magma

chamber

Lava plateaus

• Broad flat-lying plains• Stacked layers of flood

basalts • basalt flows extruded

from linear fissures • ex: Columbia Plateau• Will see columnar

jointing

Historical Eruptions5000 BC, Mt. Mazama, Oregon

– 40 km3 volcanic debris– Crater Lake

79 AD Vesuvius and Pompeii– Historic remains

1815 Mt. Tambora, Indonesia – 30 km3 volcanic debris– "year without a summer

1883 Krakatoa, Indonesia – 18 km3 volcanic debris– Heard round the world

1902 Mt. Pelee, Martinique (Carribbean) – nuee ardente killed 28,000 instantly

May 18, 1980 Mt. St. Helens, Washington State – 1 - 2 km3 volcanic debris

June 15, 1991 Mt. Pinatubo, Philippines – 2m2 of dust & fine ash– SO2 aerosol cloud circled Earth in just 21 days– stratospheric haze caused a 1 degree temperature drop

Vesuvius and Pompeii