Download Notes Igneous Activity

Igneous Activity
10.1 Nature of Volcanic Eruptions
Volcanic Eruptions
A.
Factors that determine
the violence of an
eruption
1.
2.
3.
B.
Composition (Si, Fe, Mg)
Temperature
Dissolved gases
Viscosity of magma
1.
A measure of a materials
resistance to flow –
(how “thick” it is)
B. Viscosity of Magma (con’t.)
2) Factors affecting
viscosity
a.
Temperature (high = easy
flow= low viscosity
Low temp = flows slowly
=high viscosity
b.
Composition
1. Amt of silica is high,
then,Viscosity - high,
example – felsic granite
or rhyolite
2. Amt of silica is low
Viscosity is low,
example– mafic basalt or
gabbro
B. Viscosity of Magma
2. Factors affecting viscosity (con’t)
Gases trapped
Felsic rock
c. Dissolved gases
1. H2O & CO2
2. Expand as they near
the surface
3.
Gases easily
Escape
Mafic rock
(The power to explode)
4. The violence of the
eruption is related to
how easily gases can
escape
a. Fluid magma=Easy
escape
b. viscous magma =
violent eruptions
Materials Associated with volcanic
eruptions
A. Lava flows
Pahoehoe lava
Aa lava
1. Basaltic -Fluid (dark,
dense)
2. Types of
basaltic(mafic) lava
flows
a. Pahoehoe – rope like
texture (typically
seen)
b. aa- jagged, sharp
edges
B. Gases
1. 1-5 % of weight
Materials associated w/volcanic eruptions
2.
Types of pyroclastics
a.
b.
c.
d.
e.
Ash – very fine glassy
fragments
Pumice – “frothy lava” gas
escapes at surface, leaving
holes
Lapilli – walnut sized pieces
Cinders – pea sized pieces
Larger than lapilli
1.
2.
Lava blocks – hardened
chunks of lava
Lava bombs – molten lava
often streamlined as it falls
through the air.
 Ash Cloud
Micro view of ash 
Cinders
Lapilli 
Lava blocks and bombs
Note the aerodynamic shape
They take on as they fall
Through the air
Volcanoes
A. General features
1. Opening at the top
a. Crater steep, walled
depression
b. Caldera – same as
crater, but larger (1
km or more in
diameter
Sunset Crater
Yellowstone Caldera is known as a “Super Volcano”
(Note the size of the caldera and how far there would be significant ash deposit )
2. Vent- the tunnel (conduit) that connects
magma chamber to surface (crater)
Ancient vent
Tourists near multiple small vents
Underwater vent
Volcanoes
B. Types of volcanoes
1. Shield
a. Broad, slightly domed
b. Primarily basaltic lava
c. Very large (large area,
not height above sea level)
d. Produces large
volume of lava
e.
Example: Mona Loa,
Hawaii
Shield Volcano
Mona Loa
2. Composite or (Strato)
a.
b.
c.
d.
e.
Very large, very high
elevation, symmetrical, and
usually snow capped
Interbedded layers of lava
and pyroclastics
Most violent due to its felsic
composition
Produces a Nuee ardente –
fiery cloud of hot gases
infused with ash. Flows
down at great speeds
exceeding 200 km/hr
Produces a Lahar – huge
mud slide produced when
snow at peak is melted
quickly
Nuee Ardente-firey cloud
a pyroclastic flow traveling at
Speeds past 400mph and at
Temperatures that exceed
1500 degrees F
Very powerful, very fast,
difficult to escape
Steel re-bar bent by the blast of a nuee ardante
https://www.youtube.com/watch?v=8f9TbC88-40
https://www.youtube.com/watch?v=u2vvKFkuPbk
Lahar - mudflow or debris flow composed of a slurry of
pyroclastic material, rocky debris, and water.
The material flows down from a volcano, typically along
.
a river valley
Often the “killer”
Part of a volcano
https://www.youtube.com/watch?v=3XMS-quxdGg
Volcanoes
3. Cinder Cone
a.
Built from ejected lava
material
a. Steep slope, small in size
b. Frequently occurs in groups surrounding a large stratovolcano
c. Sunset Crater, Flagstaff, AZ
Sunset Crater
Paracutin in Mexico
Paracutin
At the beginning of the
eruptions
After the
eruptions in
1943
By 1952 the
volcano
became
dormant
Distribution of Igneous Activity
Volcanoes are found
Along Plate Margins
Famous examples:
Japan – Mt. Fuji
Philippines – Mt. Pinatubo
Mt. mayon
Indonesia - Tambora,
Krakatau,
Ocean to Ocean
Plate Boundary
Famous Examples: El Chicon, Villarrica
Mt. St. Helens, & Mt. Rainer
Ocean to continent plate
boundary
Ring of Fire- the Pacific Rim is encircled by volcanic activity
Intraplate Volcanism- volcano erupts in the middle of a plate
Hawaiian
Islands
Known as “Hot Spots” in the middle of
a tectonic plate
Unusual “hot spot” on a plate boundary
Iceland
Azores