volcanoes

volcano

a vent in the crust where molten material are ejected

magma

molten rock from within the earth

magma chambers

collect material and cause buildup of pressure over time that eventually erupts

active volcano

have erupted in the past 10000 years

dormant volcanoes

have not erupted in the past 10000 years but have potential to erupt

extinct volcanoes

will not erupt ever again

factors that determine whether a volcano erupts violently or quietly

magma composition, temperature and amount of dissolved gasses

viscosity

a substances resistance to flow

the higher the viscosity….

the slower the lava moves

viscosity is directly related to the

amount of silica content

dissolved gasses

gases trapped in magma provide the force to eject the molten rock from the vent

as magma moves closer to the surface what happens

the pressure is lessened and gases can escape

basaltic lavas are

more fluid ,low silica

pahoehoe lava

looks like braids in a rope

Aa lava

rough ,jagged blocks

pillow lava

created by rapid cooling of the lava by cold water in all sides which forms the pillow shaped bodies

when does pillow lava form

when eruptions occur underwater particularly when there is a relatively low eruption rate

pyroclastic materials

particles that produce in volcanic eruptions

pyroclastic surge

a low density volcanic flow higher proportion of gas than rock

pyroclastic surge is very

very fast and causes turbulent ash cloud

pyroclastic flow

a higher density volcanic flow , higher proportion of rock than gas

pyroclastic flow immediately

follows a surge

tephra

rock fragments and articles rejected from the volcano during an eruption

what are the largest piece of tephra

blocks and bombs

what are the most common gases in an eruption

O2 and CO2

anatomy of a volcano

a mountain formed of lava and/or pyroclastic materials

crater

is the depression at the summit of a volcano or that which is produced by a volcanic impact

a conduit or pipe

carries gas rich magma to the surface

shield volcanoes

are broad and large, gently sloping volcanoes and built from fluid basaltic (thin) lavas.

cinder cones

small volcanoes built primarily of pyroclastic material ejected from a single vent

Angle of a cinder cone

steep slope angle

composite volcanoes

composed of both lava flows and pyroclastic materials

composite volcanoes are

adjacent to the pacific ocean, large size

the most violent type of activity

composite volcanoes

calderas

are large depressions in volcanoes formed by collapse

lava plateaus

fluid basaltic lace extruded from crystal fractures called fissures

fissure eruption

volcano eruption from a crack in the ground

lava dome

large , mound shaped protrusion formed by thick lava

cinder cone has

no lava

describe cinder cone

violent, high silica high viscosity, small, all pyroclastic materials

describe composite volcanoes

huge, mix of lava and pyroclastic materials, high silica high viscosity, violent

describe shield volcanoes

huge, all lava, quiet,low silica low viscosity

which lava flow are quiet

pahoehoe, Aa, pillow lava

which lava flow is violent

pyroclastic surge, flow and tephra

this volcano is least likely to form above a subduction zone

shield volcanoes

where does pillow lava form

when lava flows into water

differences between lava plateau and lava dome

lava domes are steep sided , rounded and created by viscous lava and lava plateaus are flat or gently sloping area formed by extensive lava flows .