Transcript Erupting volcano - Mrs. Feigenbaum`s Science Classes

Volcanoes
Chapter 9
What is a volcano?
• A volcano is an opening in the Earth’s
surface.
• Ash and lava come out and build up
forming a mountain.
• The word, ‘volcano’ comes from the name
Vulcan, who was the Roman god of fire.
Activity of Volcanoes
Volcanoes can be:
• Active - has had at least one eruption during
the past 10,000 years. An active volcano might
be erupting or dormant.
• Erupting volcano is an active volcano that is
having an eruption...
• Dormant volcano is an active volcano that is not
erupting, but supposed to erupt again.
• Extinct - has not had an eruption for at least
10,000 years and is not expected to erupt again
in a comparable time scale of the future.
Parts of a volcano
• Crater – opening of the volcano
• Vent – main tube running through volcano
• Side vent – vent that runs outward from
main vent
• Magma Chamber -reservoir of magma in
the earth's crust where the magma may
reside temporarily on its way from the
upper mantle to the earth's surface
How volcanoes form
• Heat and pressure inside the Earth cause
rocks to melt.
• Magma rises up because it is less dense
than the rock around it.
• Magma reaches the surface and flows out
of vents – sometimes through cracks.
• Mountains build up as lava and ash flow
out.
How volcanoes form
Where do we find volcanoes?
• Most volcanoes are found along plate
boundaries:
– Where plates move apart
– Where plates move together
• Some volcanoes are found over hot spots.
– Hot spots are areas inside the Earth where it
is hotter than nearby areas.
Where do we find
volcanoes?
Where do we find
volcanoes?
Plate Boundary Types
Divergent Boundary – where plates move apart.
Example: Iceland sits
on the Mid-Atlantic
Ridge – has many
volcanoes
Divergent Boundary
Ridges – mountain
ranges that form.
New crust is formed
Rift – valleys between
the ridges – where
volcanic eruptions
occur
Newer crust
Older crust
Plate Boundary types
Convergent Boundary – where plates move
together. Can occur between:
– Ocean and continental plates – most common
– Continental and continental plates
– Ocean and ocean plates
Ocean – Continental
convergent boundary
•A subduction zone forms– where one plate
moves under the other
– Ocean crust is more dense and moves under
continental crust.
– Rocks on the subducted plate melt and the magma
rises to form volcanoes on the other plate.
•A trench forms – deep valley
•Volcanic arcs form on continental plate.
Convergent Boundary
Convergent Boundary
Ocean – Ocean
Convergent Boundary
• Subduction may still occur forming island
arcs.
trench
Example:
Japan
Continental – Continental
Convergent Zone
• Both plates crumble and pile up forming
mountains – but not volcanoes.
• Example:
Himalayas
Hot Spots
• Areas of the mantle that are hotter than
other areas.
• They melt rock which gets forced up
toward the crust.
• If it occurs under water, it can form
volcanic islands, like Hawaii.
• Plates move, but hot spots don’t, so
volcanoes can become extinct if they no
longer sit over a hot spot.
Hot Spots
Hot Spots
Hot Spots
Extinct Volcanoes
• The Hawaiian islands that
are not on top of the hot
spot are extinct. Mauna
Loa and Kilauea are on
Hawaii – newest island.
• A new island is being
formed now – Loihi – it is
an underwater volcano.
Why does a volcano erupt?
• A volcano erupts when magma and gases
find a way to escape, so they burst to the
surface through a vent.
• An eruption can be quite gentle or very
violent.
What comes out
of a volcano?
•
•
•
•
Gases
Tephra
Lava
Pyroclastic Flow
Gases
• Gases include:
Water vapor, carbon dioxide, hydrogen sulfide,
hydrochloric acid, sulfur dioxide, methane, ammonia,
carbon monoxide, hydrogen sulfide
• Gases are toxic:
–
–
–
–
can cause respiratory problems
burn eyes (hydrochloric acid)
cause acid rain (hydrochloric acid, sulfur dioxide)
Suffocates people (carbon dioxide, carbon monoxide)
Tephra
• Pieces of rock and dried lava
– Vary in size – ash is smallest, then cinders,
bombs, and blocks.
– Ash can harm lungs – wear masks to keep
out of lungs.
– Large pieces of rock can hurt people and are
hot.
Lava
• Lava is melted rock flowing on the Earth’s
surface.
Pyroclastic Flow
• A fluidized mixture of
solid to semi-solid
fragments and hot,
expanding gases that
flows down the side of
a volcano
Types of Eruptions
• The way a volcano erupts is dependent
upon:
– Amount of trapped gases
– Amount of silica in magma
– Amount of water in magma
Trapped Gases
• Gases dissolve in liquids better if they are
under pressure (soda cans).
• Deep inside the Earth there is a lot of
pressure – allowing gases to remain
dissolved.
• As the magma gets closer to the surface,
pressure decreases allowing gases to
escape.
• More dissolved gases – more explosive
Silica in magma
• Magma contains substance called silica –
like sand.
– more silica – thicker lava – traps gases.
– less silica – thinner lava – lets gases out
• Gases must get through the lava to escape
– More silica –more explosive
– Less silica – less explosive
Water content of magma
• Lots of water – forms lots of water vapor –
a gas.
• Lots of water is the same as lots of gases.
• More water – more explosive
Forms of volcanoes
• The eruptions creates the volcano.
• Different types of eruptions form different
types of volcanoes.
– Less explosive volcano – is flat
– More explosive volcano – is tall
Forms of Volcanoes
• Volcanoes are classified by their
–
–
–
–
Angle of repose
Composition
Eruption type
Lava type
Shield Volcano
• Made from quiet lava flows – the lava
spreads out without building up tall.
• Volcano is flat and wide.
• Angle of repose is under 15o.
• Mountain made of lava only
• Ex: Hawaiian Islands
Shield Volcano
Cinder Cone Volcano
• Very explosive eruptions
• Tephra (Rock and solidified lava) drop
from the air as ash, cinders, bombs, and
blocks.
• Loosely packed tephra builds up
mountain.
• Angle of repose – over 30o.
Cinder Cone Volcano
Composite Volcano or
Stratovolcano
• Alternates between quite lava flows and
violent eruptions.
• Made of alternating layers of lava and
tephra.
• Angle of repose is between 15-30o
Composite Volcano or
Stratovolcano
Igneous Rock Formation
• Lava and magma cool and harden into
igneous rock.
– Lava – turns into extrusive igneous rock.
– Magma – turns in to intrusive igneous rock.
Extrusive Igneous Rock
• Rock that forms on the surface of the
Earth from lava.
• Cools quickly – there is no time to form
nice, large crystals
• May contain holes as gases escape
• Examples: basalt, pumice, obsidian
Intrusive Igneous Rock
• Rock that forms inside the Earth from
magma.
• Magma is not exposed to air so it cools
slowly and has time to form nice large
crystals.
• Examples: Granite, gabbro, diorite
Intrusive Igneous Features
• Not all the magma exits a volcano.
• Some gets stuck underground, forming
intrusive igneous features.
– Batholiths – large areas of intrusive rock
– Lacoliths – area that forms a dome shape
– Dikes – vertical sections that cross through
rock layers
– Sills – horizontal sections that rucn between
rock layers
Intrusive Igneous Features
Volcanic neck
• When a volcano stops
erupting, the magma
hardens inside the
vent.
• If the volcano erodes
away only the
solidified vent
remains – it is called
a volcanic neck.
Caldera
• Sometimes the top of
a volcano collapses
and produces a large
opening called a
caldera.
• Sometimes the
caldera fills with
water.
• Example: Crater Lake
Active volcano inside
the lake (Wizard Island)