VOLCANOES
CHAPTER 12
HOW DO VOLCANOES AFFECT PEOPLE?
WHAT CONDITIONS CAUSE VOLCANOES TO FORM?
WHAT IS THE RELATIONSHIP BETWEEN VOLCANOES AND PLATES?
SECTION 1:
VOLCANOES AND
EARTH’S MOVING
PLATES
MOST ACTIVE
VOLCANOES
• Hawaii
• Kilauea (kee low AY ah) is the world’s most active volcano
• May 1990 eruption destroyed the town of Kalapana
Gardens
• Eruptions on and off since January 1983
• Iceland
• Hekla eruption February 2000
• Iceland sits on an area where Earth’s plates more apart
• Known as the island of fire and ice
EFFECTS OF
ERUPTIONS
HUMAN
ENVIRONMENTAL
Evacuations occur
with enough warning –
people must leave
their homes.
Sulfurous gases from
an eruption mix with
water vapor to form
acid rain.
At times, everyone in
the path is completely
destroyed, homes,
cars; towns are buried
in ash.
Vegetation, lakes and
streams are
devastated by acid
rain.
HOW DO VOLCANOES
FORM?
• Deep inside Earth, heat and pressure changes cause rock
to melt
• This magma is slowly forced upward toward the Earth’s
surface
• After many, many years of this process, magma reaches
the surface and flows out through an opening called a
vent
• As the lava flows out and cools, it forms igneous rock
around the vent. The steep walled depression around the
volcano’s vent is the crater.
WHERE DO
VOLCANOES OCCUR?
DIVERGENT
BOUNDARIES
• Plates moving apart
• Iceland is part of the Mid-Atlantic Ridge and located in the
Artic Circle
• Plate separate forming rifts
• Lava flows from the rifts and as it cools, builds layers of
rock
• Sometimes, the eruptions rise above sea level, forming
new islands (like Iceland)
• Island of Surtsey was formed in 1963
CONVERGENT
BOUNDARIES
• Plates move together
• Oceanic plates slide underneath continental plates
• Andes Mountains in South America
• Volcanoes at convergent boundaries tend to erupt more
violently than others
• Island of Monteserrat Volcano
•
•
July 1995
Destroyed towns, vegetation and killed people
HOT SPOTS
• Hot rock at areas between Earth’s mantle and core is
forced toward the crust where it melts partially (this is
NOT a plate boundary)
• Hawaiian Islands (p. 333 Figure 5)
• Formed from volcanic activity over a period of 5 million
years
• Five of the islands are volcanoes
• Hot spot is stationary while the pacific plate moves
(causing the islands to actually change locations)
HANAUMA BAY, HAWAII
Formed through a series of violent volcanic eruptions, it is now a flooded crater.
HANAUMA BAY, HAWAII
A nature preserve popular among tourists for the beautiful coral reefs and wildlife
FOR TOMORROW
• Define “tephra” in your notes
• Read Section 2 pg. 336 – 343
• Bring a few colored pencils to diagram
volcanoes!
HOW IS THE EXPLOSIVENESS OF A VOLCANIC ERUPTION RELATED
TO THE SILICA AND WATER VAPOR CONTENT OF ITS MAGMA?
WHAT ARE THE THREE TYPES OF VOLCANOES?
SECTION 2
TYPES OF
VOLCANOES
ERUPTIONS
When you think about a volcanic eruption,
what do you see in your head?
• Two major factors influence how an volcano erupts:
• Water Vapor & Trapped Gases Present in the Magma
• Silica content in the magma
ERUPTIONS
TRAPPED GASES
WATER VAPOR
Example: What happens
when you shake a can of
coke and then open it?
At convergent plate
boundaries, oceanic plates
are involved.
Gases can escape quietly
or explode all at once, like
a shaken Coke.
The more water vapor
present in the magma, the
more explosive the
eruption.
SILICA POOR MAGMA
QUIET ERUPTIONS
• Basaltic Magma
• Fluid & quiet; lava pours
from the vents and runs
down the sides of the
volcano
• Types of lava (pg. 338)
• Pahoehoe- rope like,
smooth
• Aa- chunks of rocdk,
shapr
• Pillow- pillow shape
chunks, most common
type.
SILICA RICH MAGMA
EXPLOSIVE ERUPTIONS
• When plates slide
underneath each other and
the rock melts, the magma
is forced upward
• Thick magma with lots of
trapped gases
• Andesitic magma
• Granitic magma
TYPES OF
VOLCANOES
SHIELD VOLCANO
• Broad volcano with sloping sides
• Example – Hawaiian Islands
• Basaltic Lava
• What type of eruption?
• Can flow onto Earth’s surface through cracks
called fissures
• Creates flood basalts, which is where most of the
material inside the volcano comes out at
SHIELD VOLCANO
CINDER CONE
VOLCANO
• Steep sided, loosely packed
• Forms from tephra falling to the group from
explosive volcanic eruptions
• Paricutin
• February 1943
• Farmed noticed a large hole in his cornfield
suddenly had hot, glowing cinders in it. Over the
next few days, cinders were thrown into the air
from the opening, creating a cinder cone volcano
CINDER CONE
VOLCANO
COMPOSITE VOLCANO
• Some volcanoes alternate between quiet and
explosive eruptions
• Formed from a cycle of explosive and quiet
eruptions, causing lava and tephra to layer on
top of each other
• Found mostly where Earth’s plates come
together
• Example – Mount Rainer in Washington
COMPOSITE VOLCANO
THREE TYPES OF
VOLCANOES
UPCOMING
Section 1 & 2 Review Worksheet
Bill Nye “Volcanoes”
PROJECT RESEARCH DAY FRIDAY. You need to have chosen
your volcano by Friday.
Section 3 –Monday
Test – Wednesday
PROJECTS DUE THURSDAY, 1/16 AND FRIDAY, 1/17.
WHAT ARE IGNEOUS ROCK FEATURES AND HOW DO THEY
FORM?
HOW DOES A VOLCANIC NECK AND A CALDERA FORM?
SECTION 3
IGNEOUS ROCK
FEATURES