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Magma and Erupted Materials
Objectives:
Key Terms:
viscosity lava pahoehoe aa pillow lava pyroclastic flow pyroclastic material
Notes: (9-2)
Types of Magma
No matter what type of magma you have, silica
is the
main ingredient. What determines the type of magma is the percentages of
silica and present. Magmas with high silica content have a high viscosity
(resistance to flow) and are generally more explosive when eruptions
occur. All magmas also contain some degree of trapped gasses (CO2
& H2O
Explosive
eruptions:
 |
High silica percentage |
|
Large
amount of trapped gasses |
|
CO2
& H2O |
|
The more trapped gas the larger the explosion |
|
ex: Andesitic and granitic magma |
Magma
composition:
Basaltic magma
|
contains
less silica (50%) – easy flowing |
|
less
explosive – Quiet eruptions |
|
Low viscosity |
|
High melting temperature |
|
Associated with divergent boundaries and hot spots |
|
HI
Islands |
(geoimages.berkeley.edu/GeoImages/ Wells/geomorph/basalt.JPG)
Andesitic
/ Granitic Magma
|
Contains
lots of silica (60%) – thick |
|
Sometimes
explosive
– Moderate amount of trapped gasses |
|
Intermediate viscosity |
|
Intermediate melting temperature |
|
Associated
with subduction zones |
|
High
water content |
|
Mt St Helens |
(geology.csupomona.edu/alert/
igneous/andesite.jpg)
Rhyolitic
Magma
|
Contains
lots of silica (70%) – thick |
|
Very
explosive – lots of trapped gasses |
|
High viscosity |
|
Low melting temperature |
|
Associated with Continental hot spots |
|
Yellowstone
caldera |
Lava Flows
All magma that reaches the surface can be classified as Lava.
Basaltic lava is classified according to its texture.
| aa - rough containing many gas bubbles |
| pahoehoe - smooth |
| Underwater lava flows - pillow lava |
(www.rit.edu/~rhrsbi/GalapagosPages/ Pictures/Geology/aa.jpeg)
(www.isthe.com/.../photo/usgs/kilauea-2000/
pahoehoe-lava.jpg)
(www.bonin-islands.com/
what/pillowlava.jpg)
Ash and Rock Fragments
Solid fragments that are thrown from volcanoes are called pyroclastic materials. They are ejected by the trapped gases within the volcanoe and are classified according to their size.
Forms of tephra
| Ash - diameter < 2mm |
| Lapilli - diameter 2mm - 64mm |
| Bombs - diameter > 64mm |
| Pyroclastic flow - mixture of superheated gas and ash that travels down a volcano (~100km/hr) |
(volcanoes.usgs.gov/Imgs/Jpg/Tephra/
30410914-076_large.jpg)
(www.educeth.ch/stromboli/perm/
erta/northpit/icons/ja_128.jp)
(www.disastershq.com/.../volcan/
pyroclastic%20flow.jpg)