Download Platemarginsandtheirassociatedvolcanoes 2.41

Major extrusive volcanic
landforms
•Powerpoint on prezi.com
•Print out resources
•Go through each boundary and associated lava / eruption after fill in blank exercise for
each type.
•Pupils fill in table
•The pupils cut and stick resources to construct a mind map linking the information together
and giving examples and explanations. E.g. Oceanic hotpot (diagram) – shield volcano
(photo / diagram) – Hawaiian eruption (diagram) –because of mafic lava due to low silicon
content as oceanic crust –Low viscosity flows build large shield volcanoes. These are rarely
explosive as low water content, but fountains of lava can be shot up to 1,000 feet or more
by jets of gas. e.g. Mauna Loa
•Pupils the answer exam question.
How rocks melt
Add heat: Increase temperature of rocks, usually via a mantle
plume at a hot spot. Examples include the Hawaiian Islands
(oceanic hot spot) and Yellowstone continental hot spot).
Decrease pressure: Decrease the pressure on rock by
removing overlying material. This is accomplished at
spreading ridges associated with divergent plate
boundaries. This occurs at all mid-ocean ridges, but is
exposed only on Iceland.
Add water: Adding water (or any other material) will decrease
the melting temperature of rock. This process is important
in subduction zones where water is released from the down
going plate. Examples include the Andes in South America,
the Cascade volcanoes in the U.S., the Aleutians in Alaska,
and Japan and other islands in south east Asia.
Divergent plate boundaries:
Most volcanically active regions on Earth. Most
occurs ________ ________ and is not directly
observed by humans. Part of the mid-Atlantic
ridge is exposed on _______.
Characterized by basaltic volcanism. Dominated by
lava flows, explosive eruptions are _______.
Decompression of mantle material beneath
spreading ridges causes partial melting of
mantle material, resulting in _______.
Also occur in continental rifts where divergent
boundaries just starting to form (East African
Rift) and where continental crust is being
pulled apart (i.e. Colorado Plateau – Basin and
Range boundary, Cedar City area)
Divergent plate boundaries:
Most volcanically active regions on Earth. Most
occurs under oceans and is not directly
observed by humans. Part of the mid-Atlantic
ridge is exposed on Iceland.
Characterized by basaltic volcanism. Dominated by
lava flows, explosive eruptions are rare.
Decompression of mantle material beneath
spreading ridges causes partial melting of
mantle material, resulting in basalts.
Also occur in continental rifts where divergent
boundaries just starting to form (East African
Rift) and where continental crust is being
pulled apart (i.e. Colorado Plateau – Basin and
Range boundary, Cedar City area)
Convergent plate boundaries
• Subducting plates at convergent plate boundaries carry ______into the
upper parts of the mantle. At about 150 Km depths, reactions occurring in
the subducting plate release water into the overlying _________, thus
lowering the melting temperature of mantle material. The mantle
undergoes ________melting producing basalt. This basaltic magma rises
to the base of the continental crust. This magma has a temperature
(1200°C-1400°C) much higher than the melting temperature of the crust
(650°C-750°C), causing the crust to melt.
• Melting of continental crust produces magmas with _________
compositions. Mafic basaltic magmas and felsic magmas are thought to
mix, thus forming magmas of intermediate composition. Thus, subduction
zone volcanoes erupt ___________ and Rhyolite lavas, with minor
amounts of basalts.
• Because water is released from the subducting slab at a constant depth
(about 120 km), chains of ______________ tend to form along a line
directly above the 120 km zone of melting. These volcanoes tend to be
regularly spaced at about 70 km, and all are potentially eruptive at the
same time.
volcanoes / Mantle / water / partial / felsic / Andesite,
Convergent plate boundaries
• Subducting plates at convergent plate boundaries carry water into
the upper parts of the mantle. At about 150 Km depths, reactions
occurring in the subducting plate release water into the overlying
mantle, thus lowering the melting temperature of mantle material.
The mantle undergoes partial melting producing basalt. This
basaltic magma rises to the base of the continental crust. This
magma has a temperature (1200°C-1400°C) much higher than the
melting temperature if the crust (650°C-750°C), causing the crust to
melt.
• Melting of continental crust produces magmas with felsic
compositions. Mafic basaltic magmas and felsic magmas are
thought to mix, thus forming magmas of intermediate composition.
Thus, subduction zone volcanoes erupt andesite, and rhyolite lavas,
with minor amounts of basalts.
• Because water is released from the subducting slab at a constant
depth (about 120 km), chains of volcanoes tend to form along a line
directly above the 120 km zone of melting. These volcanoes tend to
be regularly spaced at about 70 km, and all are potentially eruptive
at the same time.
•
Rhyolite and andesite are often saturated with _______, so explosive eruptions are
common. ____________ can also erupt as lava flows, and Rhyolite (if dry) can erupt
to form ______ domes. Add occasional basalt flows to this mix, and we end up with
complex _________ volcanoes. These are the classic cone-shaped volcanoes we are
familiar with. Composite volcanoes consist of a mix of ___________materials and
lava flows, having a wide range of compositions (basalt to rhyolite).
•
Rhyolite and andesite are often saturated with water, so explosive eruptions are
common. Andesite can also erupt as lava flows, and rhyolite (if dry) can erupt to form
lava domes. Add occasional basalt flows to this mix, and we end up with complex
composite volcanoes. These are the classic cone-shaped volcanoes we are familiar
with. Composite volcanoes consist of a mix of pyroclastic materials and lava flows,
having a wide range of compositions (basalt to rhyolite).
Hotspot Volcanoes
• These are volcanoes that form over hot _______
of material rising from the base of the mantle
(mantle plumes). Mantle plumes interact with
either oceanic ________ or continental
lithosphere. In either case, the plume heats one
part of the lithosphere and a volcano forms
above the plume. As _______ move, different
parts of the lithosphere are carried over the
plume, resulting in a ______ of volcanoes, of
which only one is _______. Volcanoes along a hot
spot chain become older away from the active
volcanic center.
Hotspot Volcanoes
• These are volcanoes that form over hot plumes of
material rising from the base of the mantle
(mantle plumes). Mantle plumes interact with
either oceanic lithosphere or continental
lithosphere. In either case, the plume heats one
part of the lithosphere and a volcano forms
above the plume. As plates move, different parts
of the lithosphere are carried over the plume,
resulting in a chain of volcanoes, of which only
one is active. Volcanoes along a hot spot chain
become older away from the active volcanic
center.
Oceanic hotspots:
• Where a mantle plume interacts with oceanic
lithosphere
• Only basaltic magmas are produced
• Basalts have low viscosities and tend to have low water
contents.
• Lava flows are the primary product of eruptions
• Low viscosity flows build large shield volcanoes.
• Cinder cones develop near vents by fountaining lava
and very minor pyroclastic eruptions.
Oceanic hotspots:
• Where a mantle plume interacts with oceanic
_____________
• Only basaltic magmas are produced
• Basalts have low _________and tend to have low water
contents.
• Lava flows are the ________ product of eruptions
• Low viscosity flows build large __________ volcanoes.
• Cinder cones develop near vents by ____________lava and
very minor pyroclastic eruptions.
shield /lithosphere / fountaining / viscosities / primary
Continental hotspots:
With continental hotspots, melting of continental crust results in the
development of huge felsic magma chambers. Pressure builds up
within the chamber until the crust above the chamber breaks. With
a sudden release of pressure, the chamber rapidly empties itself in
massive eruptions, and the overlying crust collapses into the
magma chamber forming large calderas.
These are “super volcanoes” and represent the largest eruptions
known. No eruptions of this type have occurred during recorded
history. These volcanoes produce massive eruption columns, and
pyroclastic flows that can extend hundreds of miles. Measurable
ash falls can cover the earth, and material suspended in the
atmosphere can contribute to planetary cooling.
Continental hotspots:
With continental hotspots, melting of continental crust results in the
development of huge _______ magma chambers. Pressure builds
up within the chamber until the crust above the chamber breaks.
With a sudden release of pressure, the chamber rapidly empties
itself in massive eruptions, and the overlying crust _________into
the magma chamber forming large calderas.
These are “super volcanoes” and represent the largest eruptions
known. ____ eruptions of this type have occurred during recorded
history. These volcanoes produce massive eruption _________ ,
and pyroclastic flows that can extend hundreds of miles.
Measurable ash falls can cover the earth, and material suspended in
the atmosphere can contribute to planetary_________.
columns / No/ felsic / cooling / collapses /
Types of Lava
Rhyolite
Felsic
Andesite
Intermediate
Basaltic
Basaltic
Viscosity
Silicon
Flow rate
Temperature
Materials erupted
Frequency of
eruption
Type of volcano
Example
Plate boundary type
•Slow
• Medium
•fast
•Long dormant periods
•Regular / continuous
•Time to time
•Lava domes / Calderas
•Composite
•Shield / fissure / cinder
•Mainly Lava
•Tephra
•Tephra / lava
•70%
•60%
•50%
•900
•11000
•10000
Continental hot spots / continental – Oceanic
continental – Oceanic convergent /
Oceanic hot spots / oceanic – oceanic
Types of Lava
Rhyolite
Felsic
Andesite
Intermediate
Basaltic
Basaltic
Viscosity
Very
Increasing
Runny
Silicon
70%
60%
50%
Flow rate
slow
Medium
fast
Temperature
900 degrees
10000
11000
Materials erupted
Tephra /
pyroclastics
Tephra /
pyroclastics lava
Mainly Lava
Frequency of
eruption
Long dormant
periods
Time to time
Regular /
continuous
Type of volcano
Example
Lava domes /
Calderas
composite
Shield / fissure /
Ash cone
Plate boundary
type
Continental hot
spots / continental
– Oceanic
convergent
continental –
Oceanic hot spots /
Oceanic convergent oceanic – oceanic
/ continental –
divergent
continental
divergent
In what ways does volcanic activity
vary in relation to the type of plate
margin along which it occurs? (10
marks) GEOG 3 June 11
Mark scheme
Level 1 (1-4 marks) (Midpoint 3)
Simple statements of variation of volcanic activity between plate margins.
No specific detail or elaboration provided; or activity at one margin
discussed well.
Level 2: (5-8 marks) (Midpoint 6)
Specific statements of a range of variations. Elaboration that
demonstrates good understanding of the interrelationships between type
and frequency of volcanic activity at plate margins. May be use of case
studies to support.
Level 3 (9-10 marks) (Midpoint 9)
A fully developed answer, with good elaboration of a range of variations
between plate margins. A rounded answer with a full comparison (most of
features given in table above) of the two main types of plate margin.
Good use of case studies, though not a requirement.