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1. What is a volcano?
a. Types of lava
A-a, Hawaiian term for lava flows that have
a rough rubbly surface composed of broken
lava blocks. Sharp clinker block, slower
moving and cool in temp.
pahoehoe
• Pahoehoe is a Hawaiian term
for basaltic lava that has a
smooth, hummocky, or ropy
surface. A pahoehoe flow
typically advances as a series
of small lobes and toes that
continually break out from a
cooled crust. The surface
texture of pahoehoe
displaying all kinds of bizarre
shapes often referred to as
lava sculpture
The Ring Of FIRE
• Borders plate edges
• Mainly in Pacific Ocean as that is where
subduction is occurring the most
• Most volcano’s are at DIVERGING
BOUDARIES OR CONVERGING
• Some are HOT SPOTS
Tuff Ring: Diamond Head, Hawaii
Divergent boundary volcano’s
• Mostly underwater
• Emit gasses and pillow lava
• do break surface in Iceland and
east Africa
Divergent usually are rift eruptions
or cinder cones
Convergent Boundaries
• Due to subduction and crust
recycling
• We get more gas and silica
• More explosive cones
• Form Island arc’s- Sumatra
Island arc system
ocean-ocean plate collisions
forms volcanic island
arc shape chain of islands
Japan, Aleutians in Alaska
Hot spot volcanoes
• Can be EXPLOSIVE like convergent
boundaries (yellowstone)
• Or VERY mild like Hawaii
• Hotspot is an area that has excess heat,
the plate moves over it and creates
volcano’s
Usually for Shield Cones
Section 3-2
VOLCANIC ACTIVITY
1. How Magma reaches the Surface
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Less Dense than surroundings
Low density RISES
Still hot so find weak spot melts thru
Pressure builds
As pressure rises TEMP rises (BOYLE’s
LAW)
• Eruption!!
. Eruption
• Magma is now lava–Flows and projectiles
• Ash into atmosphere
• Gasses ejected
–WATER,N, O , C, S, Hydrogen sulfide
others
–Early atmosphere???
Inside the volcano
• Magma chamber is the pocket of
magma
• Vent is escape route. Main is largest
side are lateral vents
• Pipe is neck to chamber
• Crater is top of vent
• Magma is liquid rocks and hot gasses
Draw pg 95
• Batholith-large body of igneous rock formed
beneath the Earth’s surface by the intrusion
and solidification of magma) with a surface
exposure of 100 square km (40 square miles)
or larger.
• Stock-is a discordant igneous intrusion having
a surface exposure of less than 40 sq mi
(100 km2), differing from batholiths only in
being smaller. FLAT BASE
Laccolith
• a type of igneous intrusion that has split apart
two strata, resulting in a domelike structure;
the floor of the structure is usually horizontal.
A laccolith is often smaller than a stock
Dike runs up and down
Sill runs ----
Batholith
Evolution of Volcanoes
An active volcanic landscape
Evolution of Volcanoes
A volcanic landscape after a million years or so so
Types of volcanic eruptions
• Quiet- mainly slow flow lava,
some gas
• Pahoe-hoe and a-a lava
• Lava Tubes- cooled and hard on
top but still flowing below
Explosive eruptions
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Thick, high silica magma
Lots of gas
Pressure builds
Explosion produces ash and BOMBS
Pyroclastic Flows
• Ash, gas and cinders
thrown with force, flows
like a river, DEADLY
Products of Eruptions
Lava Flows
Pyroclastic Debris
• Bombs
• Lapilli
• Ash
Mudflows
Landslides
Gases
• Steam
• Carbon Dioxide
• H2S
• SO2
• HCl
• HF
Types of Volcano’s
• Extinct- Not active
• Dormant-Sleeping, not active in
recent history
• Active- Live has erupted, will
erupt
Other activity
• Geothermal- as magma or REMNANT
heat heats water it rises (that density
thing again) it can then form hot
springs and geysers
• Geyser is when it is forced out when
the water reaches Boiling point.
• This energy can be used for electricity
Caldera Formation