2. viscosity
• Is a substances resistance to
flow
• Temperature on viscosity easy
to see
• Mobility of lave strongly affected
by temperature
• Chemical composition of
magma has more important
affect on the type of eruption
• The more silica in magma the
greater it is viscosity
– High silica means slower
flow
– Lower silica faster flow
3. Dissolved gasses
• During eruption ,the gasses
trapped in magma provide the
force to eject molted rock
• Vent-an opening to the surface.
• Mostly water vapor and carbon
dioxide
• Fluid basaltic magma allows
expanding gases to bubble
upward and escape easily
• Most are quite
4. Lava flow
o Most lava is very fluid because
of the low amount of silica
o Flow rate at 10 to 300 meters
per hour
o Silica rich lava is slower
o When basaltic lava harden it
makes a smooth skin that
wrinkles known as Pahoehoe
o Aa is another form of basaltic
lava
o Rough jagged blocks
o With dangerously sharp edges
5. Pyroclastic materials
• When lava is extruded
• Some ejected lava may land
near the vent and forma
cone shape
• Wind will carry small partials
a long way
• The fragment ejected during
eruption range in size from
very fine dust and volcanic
dust to pieces that weigh
several tons
6. Type of volcano
• They’re three main
volcanic type
– Shield volcanoes
– Cinder cones
– Composite cones
• Anatomy of a
volcano
– Activity often begins
when a fissure or
develops in the crust
7. Shield volcanoes
• Are produced by the
accumulation of fluid basaltic
lavas
• Shape of broad slightly
domed
• Most have grown from the
deep of the ocean
• Including Hawaiian island
and Iceland
8. Cinder cones
• Ejects lava which hardens in the
air
• Range in size from fine ash to
bombs but mostly lapilli
• Produce gas rich basaltic
magma
• Come in simple shapes
• Shape determined by steep-
sided slope
• Last only a couple of weeks
• because of short life span
cinder cones are small between
30 to 300 miters
9. Composite cones
• Most beautiful but also most
dangerous
• Also known as stratovolcanoes
• Located in relatively narrow
zones
– Pacific ocean (ring of fire)
• Cascade range, mount. St.
Helen, mount. Rainier, and
mount. garibaldi
• Most activity are located in the
curved belts of volcano island
10. Lava plateaus
• Greatest volume of
volcano excrete from
fissures
• Columbia plateau was
formed this way
• Numerous fissure
erupted their
• Some go up to50 miters
thick but some only 1.6
miters thick
