GLY 150: Earthquakes and Volcanoes Spring 2005: 020805

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GLY 150 Earthquakes and VolcanoesSpring 2005
02/08/05
Lava flows at Kilauea Volcano, Hawaii
Lecture 8
Pyroclastic flows enter the ocean at Soufriere
Hills, Montserrat, West Indies
2
AnnouncementsGLY 150 Earthquakes and Volcanoes

• The next journal assignment is due this Thurs.
  If you still have questions regarding the grading
  the grading criteria please see me or the T.A.
  
• Your latest HW assignment is due this Thurs.
• Your first exam will be on Tues. 02-15-2005.
• We want you to understand the material so please
  come to see us if you are still unsure about any
  of the topics discussed in class
  
• Test questions will can come from the text,
  quizzes, and lectures
  
• Test questions will be multiple choice,
  true/false, and matching
  
• I will answer questions in class on the Thurs.
  before the exam so please come with questions
  
• Instructor office hours have changed to Mon.
  200-300 and Wed. 200-300

3
Figure Sources

• Diagrams of each of the fault types are shown in
  your Natural Disasters test (Chapter 3)
  
• Figures 3.8 through 3.13 are particularly
  helpful
  
• Remember, use your texts to supplement the
  lecture notes. Many of the same figures can be
  found there
  
• I have placed asterisks on the websites that most
  of the other figures came from. You should
  definitely look at these sites, read the material
  related to the figures, and be sure that you are
  well acquired with the figures.
• The last question on this weeks homework session
  is designed help relate the different faulting
  terminology and provide a study guide for your
  first exam.

4
Events this QuarterSpring 2005
5
Where is Magma Erupted?

• a. Mid-Ocean Ridges
• Greatest volume of erupted magma, basaltic
• b. Subduction Zones
• Slab sinks and water migrates into overlying
  mantle
  
• Lowers melting temperature of rocks so that they
  melt
  
• Ocean-ocean subduction zones - island arcs
• Oceanic-continental subduction zones - long,
  narrow mountain ranges
  
• c. Within a Tectonic Plate
• Hot mantle plumes (i.e. hot spots), perhaps
  rising from core-mantle boundary
  
• e.g., Hawaii, Iceland

6
Where Volcanoes Occur
Intraplate Earthquake

• Volcanism

No volcanism at continent-continent collision
zones or transform boundaries
Modified from Dynamic Earth http//pubs.usgs.gov/
publications/text/Vigil.html
7
Worldwide Distribution of Volcanoes
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Magma GenerationProcess

• As subducted slab heats up, fluids and other
  volatiles driven from subducting slab (100-200 km
  depth)
  
• Water filled ocean sediments are primary source
  of fluid
  
• Fluid rises into overlying mantle wedge where it
  causes partial melting
  
• Volatiles decrease the melting temperature of
  materials in wedge
  
• Volatiles increase magmas explosivity
• Resulting magma rises buoyantly (brut force or
  through cracks) into the overlying crust, thereby
  supplying magma for arc volcanism

9
Subduction ZonesWhy is the Subduction Zone
Volcanism Explosive?

• Magma produced at
• subduction zones
• Is high viscosity so that bubbles cannot
  expand/escape
  
• Has a high silica content (derived from melting
  of crustal rocks)
  
• Erupts at lower temperature
• Contains a lot of volatiles
• Ocean sediments atop subducted oceanic plate
  contain lots of water
  
• Carbonate from marine animals produces carbon
  dioxide when heated
  
• Mantle wedge
• Release of volatiles from the crust when heated
  by ascending magma

• REMEMBER Erupted magma is NOT derived from
  melting of the subducted oceanic plate instead
  derived from melted material in the mantle wedge
  (induced by raising volatiles)

10
Hot SpotsFormation of Hot Spot Tracks

• Plumes are stationary for millions of years
• Provide a continuous source of magma
• As the tectonic plate moves over stationary
  mantle plumes, a line of volcanoes is formed
  
• Only the volcanoes immediately above the plume
  are active
  
• As volcanoes move away from the plume they become
  extinct and the ocean starts to erode them

11
Volcanic BehaviorViscosity

• Viscosity Ability to flow
• The lower the viscosity the more fluid the
  behavior
  
• Water (low viscosity) flows faster then honey
  (high viscosity)
  
• Low viscosity magma flow like ice-cream on a hot
  day
  
• High viscosity magma hardly flows at all
• Higher Temperatures lowers viscosity
• Silica and oxygen content increase the
  viscosity
  
• Increased content of minerals (i.e. crystallized
  minerals) increases the viscosity

12
Factors Affecting Magma ExplosivityVolatile
Content

• Volatile Content how much gas is contained in
  the magma
  
• Pepsi has a higher volatile content than water
• Volatiles include water/steam, carbon dioxide,
  etc.
  
• Gas content can range from 5
  (Mt. St. Helens) by weight
  
• The higher the volatile content, the more
  explosive the magma

Mageik Volcano, Alaska
http//volcanoes.usgs.gov/About/What/Monitor/Gas/s
ample.html
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Volcanic BehaviorVolatile Content

• Volatile
• Dissolved gas contained in the magma
• Solubility in magma increases as pressure
  increases and temperature decreases
  
• Analogues to a soda pop under pressure by the
  bottle cap.
  
• When the cap is removed, reducing the pressure
  volatiles (CO2) gas escapes
  
• As the uncapped bottle warms, more volatiles are
  released (i.e. the soda goes flat)
  
• In low viscosity magmas gas easily escapes so
  pressure in the magma does not build up leading
  to non-explosive eruptions
  
• In high viscosity magmas gas becomes trapped in
  the magma causing pressures to increase.
  
• When the pressure is reduced, the dissolved
  gasses, the gasses expand in volume.
  
• Because they cannot escape the high viscosity
  magma an explosion results

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Formation of Explosive EruptionsBubble Formation
(a.k.a. vesiculation)

• As the pressure decreases as magma rises to the
  surface, bubbles form when volatiles initially
  dissolved in the magma come out of solution to
  form gas bubbles. This process is called
  vesiculation.
• As the magma rises further, the gas bubbles
  become more numerous and, and if the magma is
  fluid enough, existing bubbles also grow larger
  and escape as the magma as it rises

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Formation of Explosive EruptionsBubble
Fragmentation

• In viscous magmas, the pressure inside the
  bubbles becomes so great that they burst (a.k.a.
  fragment) allowing the gas inside the bubbles to
  suddenly and catastrophically expand
• This sudden expansion of gas is what propels
  explosive eruptions (gas thrust region)
  
• Once volatiles are expended in main explosive
  eruption, thick viscous lava flows may follow
  
• Results in alternating ash and lava layers
  observed at stratovolcanoes

Buoyant Plume
Magma Chamber (dissolved gasses)
Similar to figure 6.8 in your text
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Where are the Major Volcanoes?

• 80 are located at convergent boundaries,
  primarily subduction zones (explosive)
  
• 900 around the Pacific Ring of Fire (primarily
  in New Zealand, Japan, Alaska, Mexico, Central
  America, and South America)
  
• 250 in the Mediterranean
• Approximately 20 are located along mid-oceanic
  ridges/spreading centers (effusive)
  
• A small percentage are located at hot spots far
  from plate boundaries (e.g., Hawaii) (effusive)

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Associated landform
Volcanic Types
Icelandic
Hawaiian
Stromboliian

• Different eruptive types lead to different
• explosivities (measure of eruptive power)
• landforms

Vulcanian
Plinian
Caldera
From Natural Disasters, Figure 6.16 in your text
18
Volcanic Explosivity Index (VEI)Historic
Eruptions

• In the last 10,000 yrs
• 4 VEI 7 eruptions
• 39 VEI 6 eruptions
• 84 VEI 5 eruptions
• 278 VEI 4 eruptions
• 868 VEI 3 eruptions
• 3477 VEI 2 eruptions

http//volcanoes.usgs.gov/Products/Pglossary/,
see page 167 in your text
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Volcanic BehaviorSummary

• Using the 3 Vs (viscosity, volatiles, volume) we
  can predict volcanic landforms

From Natural Disasters, Table 6.7 Class Text
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Quiz
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Quiz 4 Explosivity

• (1 point) As VEI increases, the
• volume of material erupted decreases
• time between similar sized eruptions decreases
• explosivity of the eruption increases
• worldwide yearly rate of occurrence of this size
  of eruption increases
  
• height of the eruptive column typically
  decreases
  
• (1 point) In an eruption, fragmentation refers to
  the
  
• nucleation of gas bubbles
• explosive shattering of gas bubbles as they
  approach the surface because of high pressure
  inside the bubble
  
• process of vesiculation
• process of driving volatiles from the subducting
  plate via heating
  
• differentiation of magma into viscous and
  non-viscous magmas
  
• (2 points) Write 2-3 complete sentences
  discussing concepts you are having difficulty
  with, topics you think are particularly
  interesting, specific questions you might have,
  or topics you want to hear more about, etc.

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Icelandic EruptionsIceland
http//pubs.usgs.gov/publications/text/Krafla.html
Krafla Volcano, 1977-1984

• Combination hot spot and divergent plate boundary
  (oceanic-oceanic)
  
• As tectonic plates moved about surface of the
  earth, oceanic spreading center coincidently
  moved over a hot spot
  
• Double dose of volcanism created the topographic
  high which is Iceland
  
• The only place on the mid-ocean ridge system that
  rises above sea-level

http//pubs.usgs.gov/publications/text/understandi
ng.htmlanchor5567033
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IcelandFissure Eruptions

• Fissure eruptions occur when stretched crust
  finally breaks and contracts back to an
  unstretched condition
  
• Similar to elastic rebound model for earthquakes
• Any single rifting event on 10s km long (a small
  fraction of entire rift system)
  
• Extensive ground cracking parallel to the rift
• Affects an area a few kms across
• At any one location, rift events are infrequent,
  occurring only every few hundred years

• Low Viscosity
• Low Volatiles
• Large Volume

Krafla Volcano, 1975-1984 (previous eruption 1724
-1728)
http//pubs.usgs.gov/publications/text/Krafla.html
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Icelandic Eruptions (1984 Krafla erution)

• Low Viscosity
• Low Volatiles
• Large Volume

Curtins of Fire
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Icelandic Eruptions

• Low Viscosity
• Low Volatiles
• Large Volume

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Hawaiian Eruptions

• Low Viscosity
• Low Volatiles
• Large Volume

Curtins of Fire
Spatter Cone
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Kilauea Volcano, Hawaii A Typical Rift Eruption

• Eventually, the rift eruption coalesces to a
  central vent
  
• A stage of lava fountaining ensues

• Low Viscosity
• Low Volatiles
• Large Volume

Puu O o Eruption 1983 to Present
http//volcanoes.usgs.gov/Imgs/Jpg/Tephra/
28
Kilauea Volcano, Hawaii A Typical Rift Eruption

• Low Viscosity
• Low Volatiles
• Large Volume

• Get alternating periods of lava fountaining and
  more gentle outpourings of lava
  
• Behavior depends on volatile (gas) content of
  magma
  
• Higher gas content leads to more explosive
  eruptions
  
• A cinder cone is formed at the central vent

Puu O o Eruption 1983 to Present
http//volcanoes.usgs.gov/Products/Pglossary/
29
Kilauea Volcano, Hawaii A Typical Rift Eruption

• As volatiles are expended, lava fountaining
  ceases and a lava lake is formed that fills the
  existing volcanic cone/crater
  
• Produces Shield Volcanoes

• Low Viscosity
• Low Volatiles
• Large Volume

Puu O o Eruption 1983 to Present
http//hvo.wr.usgs.gov/gallery/kilauea/erupt/1986t
o1991.html
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Types of VolcanoesShield Volcanoes

• Effusive eruptions of new volcanic material
• Average lifetime 100,000 1,000,000 years
• Both flank eruptions (eruptions from the side of
  the volcano) and summit eruptions are common
  
• Typically form above hot spots

• Low Viscosity
• Low Volatiles
• Large Volume

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Types of VolcanoesShield Volcanoes

• Broad, gentle slopes which are convex upward
  (like a warriors shield laid on the ground)
  
• Layered - built by the repeated eruption of
  fluid, low viscosity lavas
  
• Enormous volcanic edifices with huge footprint
  because
  
• Lava flows across the ground easily
• Lava can form tubes that enable lava to flow tens
  of kilometers from an erupting vent with very
  little cooling
  
• Largest volcanoes on Earth

http//volcanoes.usgs.gov/Products/Pglossary/
Mauna Loa, Hawaii
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Shield VolcanoesMauna Loa, Hawaii

• Fissure eruption on the flank of the volcano
  (a.k.a. curtain of fire)
  
• From a long vertical dike that has reached the
  surface

33
Types of VolcanoesFlood Basalts

• Thick flat lying effusive basalt flows that form
  immense plateaus
  
• Cover areas thousands of times larger than the
  largest volcano
  
• Formed when a hot spot (i.e., mantle plume)
  penetrates continental crust
  
• Associated with large emissions of potentially
  hazardous volcanic gas
  
• Eroded flood basalts generate characteristic
  topography (a.k.a. traps)

• Low Viscosity
• Low Volatiles
• Very Large Volume

34
Types of VolcanoesFlood Basalts

• Major flood basalt provinces
• India (Deccan Traps)
• 1-2 km thick (3000-6000 ft)
• Cover half-million square kilometers
• Siberia (Siberian Traps)
• Cover even larger area than the Deccan Traps
• United States (Columbia River Flood Basalts)
• Relatively small flood basalt province
• Iceland
• Ocean

http//vulcan.wr.usgs.gov/Volcanoes/ColumbiaPlatea
u/
35
Types of VolcanoesContinental Flood Basalts

• Major flood basalt provinces
• Siberia (Siberian Traps)
• Cover even larger area than the Deccan Traps
• United States (Columbia River Flood Basalts)
• Relatively small flood basalt province
• India (Deccan Traps)
• 1-2 km thick (3000-6000 ft)
• Cover half-million square kilometers
• Iceland

36
Types of VolcanoesFlood Basalt Plateaus
Great Basin

• Flood Basalts typically produce large volcanic
  plateaus with small shield volcanoes

• Low Viscosity
• Low Volatiles
• Very Large Volume

Yellowstone
37
Types of VolcanoesStombolian Eruptions

• May be relatively long-lived (yrs) with frequent
  eruptions
  
• Built-up with pyroclastic material that eroded
  quickly leaving the resistant central conduit to
  form a spectacular volcanic necks
  
• Produce cinder cones

• Low/Medium Viscosity
• Medium/High Volatiles
• Small Volume

38
Pyroclastics(a.k.a. Tephra)
Ash and Pumice

• Pyroclastic material fragments of volcanic rock
  and lava (regardless of size) blasted into air by
  explosions or carried upward by hot gases in
  eruption columns or lava fountains
• Larger fragments usually fall near volcano
• Smaller fragments may be transported far from the
  source

Blocks
Bombs
All from http//volcanoes.usgs.gov/Products/Pgloss
ary/
39
Types of VolcanoesCinder Cones

• Moderately explosive eruptions of new volcanic
  material
  
• Average lifetime 1-100 years
• Frequently form on flanks and summits of larger
  shield and stratovolcanoes
  
• Can also form independent of larger volcanic
  edifices
  
• Generally produce stombolian-type eruptions

• Low/Medium Viscosity
• Medium/High Volatiles
• Small Volume

40
Types of VolcanoesCinder Cones

• Steep conical hills of volcanic fragments that
  accumulate around and downwind of the vent
  
• Sides straight with slopes of 30 (angle of
  repose)
  
• Pyroclastic material (a.k.a. tephra) ejected
  material of all sizes (a.k.a. ash, bombs,
  blocks, etc.)
  
• Solid by the time it hits ground
• Most numerous type of volcano
• Small 10s to 100s of meters tall
• Rarely reactivated (i.e., rarely erupt a 2cnd
  time)

Red Cones, Long Valley Caldera, California
Downwind Side
http//volcanoes.usgs.gov/Products/Pglossary/
41
Types of VolcanoesCinder Cones
Kilauea Iki, Hawaii
Stromboli, Italy
Downwind Side
http//volcanoes.usgs.gov/Products/Pglossary/strom
bolian.html

• Low/Medium Viscosity
• Medium/High Volatiles
• Small Volume

Sunset crater, AZ
42
Types of VolcanoesVulcanian Eruptions

• Begins with steam explosions that remove old lava
  from the central vent
  
• Main eruptions characterized by eruption of
  viscous gas-rich magma. A cauliflower or
  mushroom shaped ash cloud develops. Lightning is
  common.
• Pyroclastic material more widespread than in
  Hawaiian or Strombolian eruptions.
  

• End of eruption characterized by viscous lava
  flows.
  
• Can produce cinder cones or stratovocanoes

• Medium/High Viscosity
• Medium/High Volatiles
• Small/Large Volume

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Volcanic EruptionsPlinian Eruptions

• Large, explosive eruptions
• Form enormous dark columns of tephra and gas that
  extend high into the stratosphere (11 km)
  
• Driven upward by buoyancy of hot gasses
• Associated hazards
• Pyroclastic flows and surges as eruptive column
  collapses
  
• Extensive ash falls
• Ash Clouds

• High viscosity
• High volatiles
• Large volume

Mt. St. Helens, Washington
http//volcanoes.usgs.gov/Hazards/What/PF/PFMSH.ht
ml
44
Types of Volcanoes Plinian Eruptions
Mt. Pinatubo, Philippines, 1991

• High viscosity
• High volatiles
• Large volume

• Produced at Stratovalcanoes
• Carries pyroclastic debris up to 50 km (30 miles)
  into the atmosphere.
  
• Can affect climate
• Generally the final phase in a major eruptive
  sequence
  
• About 1-2 occur each century
• e.g.Vesuvius and Pompeii

Abbot, Fig 6.25 in your text
45
Mount Vesuvius, ItalyPliny the Younger A.D. 79
- I

• The cloud could best be described as more like
  an umbrella pine than any other tree, because it
  rose high up in a kind of trunk and then divided
  into braches. I imagined that this was because
  it was thrust up by the initial blast until its
  power weakened as it was left unsupported and
  spread out under its own weight. Sometimes it
  looked light-colored, sometimes it looked mottled
  and dirty with the earth and ash it had carried
  up. Like a true scholar, my uncle saw at once
  that it deserved closer study and ordered a boat
  to be prepared. He said that I could go with
  him, but I chose to continue my studies.

46
Types of VolcanoesStratovolcanoes (a.k.a.
composite volcanoes)

• Explosive eruptions of new volcanic material
  extremely hazardous
  
• Average lifetime 100,000 1,000,000 years
• Both flank eruptions (eruptions from the side of
  the volcano) and summit eruptions are common
  
• Form at subduction zones

• High viscosity
• High volatiles
• Large volume

Mount Fuji, Japan
47
Types of VolcanoesStratovolcanoes (a.k.a.
composite volcanoes)

• Steep, conical volcanoes
• Slopes have a concave upward profile
• Produce both highly explosive and effusive
  eruptions
  
• Composed of alternating layers of pyroclastic
  material and viscous lava (i.e., they are
  stratified)
  
• May have secondary vents with cinder cones and
  lava domes on flanks
  
• Typically occur on the landward side of
  subduction zones

Mount Mageik, Alaska
http//volcanoes.usgs.gov/Products/Pglossary/
48
Types of VolcanoesStratovolcanoes (a.k.a.
composite volcanoes)

• Stratovolcanoes often more complex then
  introductory schematics indicate
  
• Ash layers extend further from vent than lava
  layers (lava is viscous)
  
• Many secondary (a.k.a. parasitic) cones form on
  slopes of main edifice

• High viscosity
• High volatiles
• Large volume

49
Types of VolcanoesStratovolcanoes
Mt. St. Helens, Washington
Masaya Volcano, Nicaragua

• High viscosity
• High volatiles
• Large volume

http//volcanoes.usgs.gov/Hazards/What/PF/PFMSH.ht
ml
Mt. Rainier, Washington
50
Types of VolcanoesStratovolcanoes vs. Shield
Volcanoes

• Shield volcanoes are significantly more
  voluminous than stratovolcanoes
  
• Especially true when considering the size of the
  volcano at its base
  
• Note the differing profiles (concave up vs.
  concave down) for the two types of volcanoes

http//vulcan.wr.usgs.gov/Imgs/Gif/VolcanoTypes/sh
ield_vs_composite.gif, See Fig 6.17 in your text
51
Types of VolcanoesLava Domes

• Effusive eruption of new volcanic materials
• Average lifetime 1-100 years
• Usually form after the explosive eruption of
  gas-rich magma at stratovolcanoes (thus common at
  subduction zones)

• High viscosity
• Low volatiles
• Small volume

52
Types of VolcanoesLava Domes

• Rounded, steep-sided mounds of lava formed near
  the volcanic vent by very viscous magma
  
• Magmas are typically too viscous (resistant to
  flow) to move far from the vent before cooling
  and crystallizing.
  
• Consist of one or more individual lava flows
• May plug the volcanic vent, allowing pressure to
  build up
  
• Steep sided domes may collapse, generating
  pyroclastic flows

Mount St. Helens, Washington
http//vulcan.wr.usgs.gov/Volcanoes/MSH/Images/lav
a_dome.html

• High viscosity
• Low volatiles
• Small volume

53
Lava Dome FormationMt. St. Helens, Washington

• Grow by continuously adding new layers and lobes
  surrounded by slopes of talus (broken-up, loose
  pieces of rock)

http//vulcan.wr.usgs.gov/Imgs/Gif/MSH/Graphics/Do
mes/dome_growth_schematic_80-83.gif
http//vulcan.wr.usgs.gov/Imgs/Gif/MSH/Graphics/Do
mes/msh_lobes_80-81.gif
54
Types of VolcanoesLava Domes
http//vulcan.wr.usgs.gov/Glossary/Domes/images.ht
ml
Katmai Volcano, Alaska
High viscosity Low volatiles Small volume
Near Mono Lake, California
Mt. Lassen, California
55
Volcanic EruptionsPhreatic Eruptions
Mt. St. Helens, Washington, April 4, 1980

• Produced when groundwater comes in contact with
  hot rock or magma and flashes to steam
  
• No new magma is expelled
• Only preexisting rock is erupted

http//volcanoes.usgs.gov/Products/Pglossary/Hydro
VolcEruption.html
56
Types of VolcanoesCalderas

• Large, circular, steep-walled depression at the
  summit of a volcano
  
• Up to 10s km in diameter
• Walls up to 100s m high
• Formed in hours to days
• Average lifetime 100,000-1,000,000 years
• Differ from craters which are smaller (circular depressions formed by the explosive
  evacuation of rock during eruptions

Aniakchak Caldera, Alaska
http//volcanoes.usgs.gov/Products/Pglossary/

• High viscosity
• High volatiles
• Very large volume

57
Types of VolcanoesCalderas
High viscosity High volatiles Very large volume

• Formed by
• Explosive disintegration of the top of a volcano
  (typically a stratovolcano)
  
• Collapse of the top of a volcano into an
  underground magma reservoir due to a loss of
  structural support after magma has withdrawn or
  been erupted
• Volcano collapses or subsides into emptied space
• Caldera collapse associated with great eruptions

58
Types of VolcanoesOverview

• Volcanoes come in a variety of sizes and shapes
• Their shapes are a result of the
• types of magma erupted
• processes and types of eruptions that formed them

mid-ocean ridge volcanism continental flood b
asalts
59
Types of VolcanoesOverview

• Flood Basalts

http//vulcan.wr.usgs.gov/Photo/Pictograms/volcano
_types.html
60
Types of Volcanoes
http//vulcan.wr.usgs.gov/Glossary/VolcanoTypes/vo
lcano_types.html