2. VOLCANO REVIEW
Review Questions:
1. On what kind of plate boundaries do
volcanoes appear?
2. What is the difference between magma and
lava?
3. THREE TYPES OF VOLCANOES:
*There are three types of volcanoes:
*Shield Volcano
*Cinder cone Volcano
*Stratovolcano
4. *WHY DO WE HAVE DIFFERENT TYPES OF
VOLCANOES?
The process of magma formation is different
at each type of plate boundary.
Therefore, the composition of magma differs
in each tectonic setting.
*Tectonic settings determine the types of
volcanoes that form and the types of
eruptions that take place.
5.
6. *SHIELD VOLCANO
Form from many
layers of “runny” lava.
Very wide, not too
steep.
Biggest type of
volcanoes
Tallest mountain in
the world is Mauna
Kea (measures from
sea floor to top)
non explosive
eruptions
8. TECTONIC SETTING (LOCATIONS)
Darwin, a
shield
volcano in
the
Galapagos
Islands.
Shield-type volcanoes are almost exclusively located in an oceanic
setting, in the “middle” of oceanic basins or as isolated islands,
typically somewhat distant from continental shorelines.
9. MORPHOLOGY (SHAPE and SIZE)
Fernandina,
a shield
volcano in
the
Galapagos
Islands.
Shield volcanoes tend to have very gentle (low-angle) slopes,
sometimes referred to as the “overturned soupbowl” profile.
Although not as visually dramatic as stratovolcanoes, they are
generally much larger, particularly in diameter.
10. ACTIVITY Continued;
San Martin,
a small
shield
volcano off
the coast of
Baja,
California.
These volcanoes can form during single long-term effusive eruptions
and remain active for tens to hundreds of thousands of years. During
their lifespans, dormant intervals may also last thousands to tens of
thousands of years.
11. *CINDER CONE VOLCANO
Smallest type of volcano
Most common
Made from pyroclastic material (material
shot out of a volcano)
Form a large crater
Explosive!
13. CINDER CONES
Cinder cones, also known as scoria cones, represent the smallest type
of volcano, rarely exceeding ~1000 ft in height. They are entirely
composed of pyroclastic materials (volcanic ash). They are quite
common and associated with both composite or shield volcanoes.
They typically occur on the flanks (sides) of these volcanoes where
secondary vents or fissures have opened up.
Scoria cone near the summit of Mauna Kea,
Hawaii.
La Poruna, Chile
Sunset crater, Arizona
14. CINDER CONES
A small cinder cone (~225m high, ~200m in diameter) located on
Barren Island, a part of the Andaman Islands chain situated just
north of Indonesia.
15. CINDER CONES
Kwohl Butte cinder cone is one of a chain of small cones trending
south of Mt. Bachelor (a composite volcano) in the Cascade range of
Oregon. It is ~ 12,000 years old.
16. CINDER CONES
The Cerro Negro cinder cone represents one of Nicaragua’s youngest
volcanoes. It was born in April of 1850 and has grown to a height of
250 m.
18. *STRATOVOLCANO OR COMPOSITE VOLCANO:
Eruptions alternate between explosive and
non-explosive.
Sometimes they have runny lava layers,
other times the have pyroclastic materials
form layers.
Have a wide base and steep sides.
Have a crater
Mount Fuji
20. MORPHOLOGY (SHAPE and SIZE)
Mayon, the
most active
composite
volcano in
the
Philippines.
Stratovolcanoes are what most people associate with the word
volcano. These towering peaks rise hundreds to several thousand
meters above their surroundings, often visually dominating the
landscape around them. They tend to be steep-sloped.
21. MORPHOLOGY (SHAPE and SIZE) Continued;
Niragongo,
an active
composite
volcano
located on
the border
of Rwanda
and Zaire,
East Africa.
The relatively steep profile of stratovolcanoes are due to their rock
makeup. They are formed of stratified layers of both viscous lava
flows and fragmental material (volcanic ash).
22. ACTIVITY
Kamen (left)
and
Kliucheyskoi,
two of
Kamchatka’s
highest
composite
volcanoes.
Due to the viscous nature of the lavas associated with composite
volcanoes, they tend to “plug” up. If the pressures are great enough,
these volcanoes may literally “blow their top”, and can be quite
violent and dangerous!
23. ACTIVITY Continued;
Colima,
Mexico’s
most active
composite
volcano.
Some stratovolcanoes may form in a few thousand years, but remain
active for tens to hundreds of thousands of years. During their
lifespans, dormant intervals may also last tens of thousands of years.
24. *2 TYPES OF ERUPTIONS
*Explosive: volcanoes
that build enough
pressure to blow its
top, sending
pyroclastic material
into the air.
*Non explosive: Build
only enough pressure
to allow lava to run
down its sides.
25. NON EXPLOSIVE ERUPTION
Mafic: refers to rocks and magma rich in iron
and magnesium.
This type of lava that is very runny.
As magma nears the surface there is little
pressure, causing gasses escape easily.
Magma low in Silica have quiet eruptions
26. EXPLOSIVE ERUPTIONS
Felsic: means magma with high silica and
feldspar content.
Felsic magma traps water and gas bubbles,
which leads to lots of pressure.
Silica acts like a cork
Explosive eruptions are caused by a build up
of high pressure.
Convergent zones contain lots of water,
therefore have explosive eruptions.
27. *PYROCLASTIC MATERIALS
*Material that is thrown into the air during an
explosion.
*Volcanic bombs: large blobs of magma that
harden in the air.
Lapilli: pebble size rocks
Volcanic ash: tiny powder like material
28.
29. *FOUR TYPES OF LAVA
Aa: lava that is thick and sharp
Pahoehoe: lava that forms thin crust and
wrinkles
Pillow lava: lava that erupts under water, has
a round shape
Blocky lava: cooler, lava that does not travel
far from eruption, jagged when it dries.
31. *PAHOEHOE:
*lava that forms thin
crust and wrinkles
32. *PILLOW LAVA
*lava that erupts
under water, has a
round shape
33. *BLOCKY LAVA
*cooler, lava that does
not travel far from
eruption, jagged when
it dries.
34. WHY DO COMPOSITE VOLCANOES TEND TO
BE EXPLOSIVE AND SHIELD VOLCANOES
NON-EXPLOSIVE??
1) CHEMISTRY (COMPOSITION) OF LAVA
2) LAVA TEMPERATURE
COMPOSITE SHIELD
- Higher silica content of lavas -Lower silica content of lavas
make them more viscous (thick). make them more fluid (runny).
- Lava temperatures are - Lava temperatures are quite
generally a few hundred degrees hot, ~ 2200oF, making it easier
cooler than those of shield for these lavas to “flow like
volcanoes, making the lavas water”.
“thicker” in consistency.
35. OTHER CHARACTERISTICS ASSOCIATED
WITH COMPOSITE AND SHIELD
VOLCANOES
Both volcano types commonly contain abundant gases dissolved in
the magma (especially composite-type).
GAS EMISSIONS:
Water vapor (steam) is the most common gas emitted by a volcano
(70-90%). Other common gases include; CO2, CO, SO2, SO, and a
variety of other sulfurous (stinky) gases.
It is the buildup of gas pressures that commonly cause composite
volcanoes to violently explode when they get “plugged up”.
ASH EMISSIONS:
Pyroclastic (means “hot particle”) eruptions “volcanic ash” are
particularly common with composite volcanoes and uncommon with
shield volcanoes.
36. WHY ARE THESE TWO VOLCANO TYPES
(COMPOSITE-SHIELD) SO DIFFERENT???
It is most fundamentally tied to the source material from which these
two types of volcanoes come from, and this ties back to their tectonic
setting!!!
Recall, that composite volcanoes primarily have a “continental”
setting, and shield volcanoes have an “oceanic” setting.
38. REVIEW
1. What determines the type of volcano found
in a particular location?
2. What type of lava creates wrinkled lava
flows?
3. What type(s) of volcanoes have the most
explosive eruptions?
