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
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