Download Associated with non-explosive eruptions.

Ch. 18 Notes Day 1
10/13/16
Objectives
SWBAT explain the relationship between
the strength and type of a volcanic
explosion and the type of rock and debris
it produces
SWBAT explain the importance of Silica
content in volcanic products an how it
controls the strength of the explosion.
Ring of Fire
The Ring of Fire is a continuous,
25,000 mile long series of 452
oceanic trenches, volcanic arcs,
and volcanic belts associated
with numerous plate boundaries
in the Pacific Ocean Region
Volcanic eruptions produce three major
rock types based on the type of
eruption.
Basalt
Andesite
Rhyolite
Basalt
Low silica content (50%)
Rock Type: Mafic
Low viscosity
Low gas content
Temperature: 1100 C
Associated with
non-explosive eruptions.
Produces large basalt floes
Material Source: Oceanic crust at divergent
boundaries
Shield Volcano
 Quiet, non-explosive eruption (lava comes out slowly)
of usually basaltic lava.
Made of layers of solidified basaltic lava
Gentle slopes
Andesite
Medium silica content (60%)
RockType: Mafic/Felsic (Intermediate)
Medium Viscosity
Medium Gas Content
Temperature: 1000 C
Associated with semiexplosive to explosive
eruptions.
Material Source: Oceanic & Continental crust at
convergent oceanic-continental boundaries.
Composite or stratovolcanoes
Repeated cycle of non-explosive and explosive eruptions
Built from alternating layers of tephra and lava
Typically produce andesite and rhyolite
Tall and majestic
Rhyolite
High silica content (70%)
Rock Type: Felsic
High viscosity
High gas content
Temperature: 800 C
Associated with highly
explosive eruptions.
Material source: Continental crust from
continental-continental convergent
boundaries
Cinder Cone Volcano
Explosive Eruptions
Steep Slopes built from tephra (ash and rocks)
Smallest of all volcanoes
Usually form at edges of larger volcanoes
Usually made from basalt and rhyolite
Ch. 18 Notes Day 2
Objectives
SWBAT explain the anatomy of a
volcano
SWBAT the difference materials that
are ejected from a volcano during
an eruption and their effect on the
surrounding environment
Caldera Volcano
Most Explosive Eruptions
Volcano literally blows itself up and creates
a large crater
Typically produce rhyolite
Anatomy of
a Volcano
Tephra – mixture of ash, rocks, lava, and pyroclasts (lava
that hardens in mid air) thrown from a volcano as it erupts.
ASH –
Very finegrained
fragments
(< 2 mm)
BOMBS –
Fragments
(> 64 mm)
BLOCKS –
Very large pyroclasts
launched from a
volcano
LAPILLI –
Pea- to walnut-size
pyroclasts (2 to 64
mm). They often look
like cinders
Gasses Given off During Eruptions
The most abundant gas is water vapor (H2O), followed by
carbon dioxide (CO2) (green house gas, contributes to global
warming)
sulfur dioxide (SO2) (very poisonous)
Secondary gases are also include:
hydrogen sulfide (H2S),
hydrogen (H)
carbon monoxide (CO)
hydrogen chloride (HCl)
 hydrogen fluoride (HF)
helium (He)
Magma vs. Lava
Magma is molten
rock trapped
BELOW the earth’s
surface
Lava is molten rock AT or
ABOVE the earth’s surface
Pyroclastic Flows
• Mixture of ash, gases, and
tephra that “avalanche”
from a volcano
• Hot (> 700 °C)
• Can be faster than 100 mph
Hot Spot
Unusually hot regions
of Earth’s
mantle where hightemperature
plumes of magma rise
to the
surface.
Can be linked to the
path of
convergent plate
boundaries