Volcanoes
1. Use this PowerPoint to help fill in your
guided notes
2. We will paste these notes into our
notebooks next week. Get a stamp and
turn them in when you finish.
3. Return class copy of notes.
What is a Volcano?
• Volcano is a term that refers
to:
1. An opening in Earth’s crust
through which molten rock,
ashes and gas erupt.
2. The structure that develops
around the opening in Earth’s
crust
Three Types of Volcanoes
• Shield volcano – LARGE
• Composite-Strato volcano – MEDIUM
• Cinder cones – SMALL
Shield Volcanoes
• Have broad bases and gently sloping sides
• Release lava slowly and can form huge
landmasses
• Lava flows smoothly (is NOT viscous)
– Ex. Mt. Loa, Hawaii
Composite-Strato Volcanoes
(stratovolcanoes)
• Have steep sides and
a narrower base.
• Erupt violently with
hardened lava flow
and pyroclastic
material.
• Ex: Mt. Shasta
• Lava is very viscous
(doesn’t flow well)
After a violent eruption, composite volcanoes may remain fairly
quiet for a long time. Beneath the surface, magma and gases are
building up for the next explosive eruption
•
JUST FYI-read and rest your writing hand for a bit.
A pyroclastic flow is a fluidized
mixture of solid to semi-solid
fragments and hot, expanding gases
that flows down the flank of a volcanic
edifice.
• They move much like a snow
avalanche, except that they are
fiercely hot, contain toxic gases, and
move at phenomenal, hurricane-force
speeds, often over 100 km/hour!!!
• They are the most deadly of all
volcanic phenomena.
Cinder Cones
• Smaller than other
types of volcanoes
• Typically form in
groups on the sides
of larger volcanoes
• Made of loose
volcanic material,
called cinders
• Ex: Sunset Crater
Classifying Volcanoes
• An active volcano is currently erupting or has erupted
recently (in geological terms)
• A dormant volcano has not erupted lately but is
considered likely to do so in the future.
• An extinct volcano has not erupted for a very long time
and is considered unlikely to do so in the future.
Distribution of Volcanoes
Volcanoes are found at
• Convergent-Subduction
boundaries
• Divergent boundaries
• HOT SPOTS: Caused by a
narrow stream of hot magma
convecting up from the Earth‘s
core-mantle boundary.
Tectonic plates move slowly
across a fixed hot spot deep
below the surface.
Hot Spots
Volcanic activity like
Yellowstone park occurs
from a hotspot under
continental plate.
Volcanic chains like the
Hawaiian Islands result
from a hot spot under
Oceanic plate.
Calderas
Caldera- A bowl
shaped depression
formed when a
volcano erupts,
empties a magma
chamber and then
collapses on itself.
(see diagram)
Great job!
• Please return your class copy and
get a stamp from the teacher.
• Review the movie notes that you will
answer on the back so that you
know what to look for as you watch.
• Please be quiet and respectful of
your classmates as they finish their
own notes.
Local Volcanoes
Magma
• Viscosity is resistance to flow.
• Rhyolitic Magma = High Viscosity =Slow Flowing Lava
• Basaltic Magma = Low Viscosity = Fast Flowing Lava
Types of Magma
• Basaltic magmas form at rifts and at oceanic hot spots.
• Andesitic magmas form at subduction boundaries.
• Rhyolitic magmas form where hot spots underlie continental
plates.
PEP TALK!