Embed Size (px)
Citation preview
1
Chapter 14…what’s the connection?
Volcanoes and Plate Tectonics…
- Subduction - Rifting - HotspotsVolcanoes are formed by:
S.2
Pacific Ring of Fire
Subduction Volcanoes
Volcanism is focused at
PLATE MARGINS.
(red dots)
S.3a
2
Pacific Ring of Fire
Hotspot Volcanoes
S.3b
• Hot mantle plumes breaching the surface in the middle of a tectonic plate
What are Hotspot Volcanoes?
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The Hawaiian island chain are examples of hotspot volcanoes.
S.4a
The tectonic plate moves over a fixed hotspot forming a chain of volcanoes.
The volcanoes get younger from one end to the other.
S.4b
The tectonic plate moves over a fixed hotspot forming a chain of volcanoes.
The volcanoes get younger from one end to the other.
3
• Iceland is an example of continental rifting.
• Iceland has a divergentplate boundary running through its middle.
• The ridge and volcanoes appear above the ocean surface.
The Mid-Atlantic Ridge: Iceland
S.5
Volcanoes and Types of Eruptions
Factors Affecting Eruptions
The Nature of Volcanic Eruptions
Factors that determine the violence of an eruption • Composition of the magma• Temperature of the magma• Dissolved gases in the magmaViscosity• Viscosity is the measure of a material's
resistance to flow.
Factors Affecting Eruptions
The Nature of Volcanic Eruptions
Viscosity• Factors affecting viscosity
- Temperature (hotter magmas are less viscous)- Composition (silica content)
1. FELSIC = High silica—high viscosity (e.g., rhyolitic lava)
2. MAFIC = Low silica—more fluid (e.g., basaltic lava)
S.6
4
Factors Affecting Eruptions
The Nature of Volcanic Eruptions
Dissolved gases • Mainly water vapor and carbon dioxide
• Gases provide the force to extrude lava
• Violence of an eruption is related to how easily gases escape from magma
- Gases escape easily from fluid magma.- Viscous magma produces a more violent
eruption.
S.7a
Magma Composition
Volcanic Material
The Nature of Volcanic Eruptions
Lava Flows• Basaltic lavas are more fluid.
- Pahoehoe lava (resembles braids in ropes) - Aa lava (rough, jagged blocks)
• Types of lava
Gases• One to 5 percent of magma by weight• Mainly water vapor and carbon dioxide
S.7b
Pahoehoe (Ropy) Lava Flow
5
Slow-Moving Aa Flow
Volcanic Material
The Nature of Volcanic Eruptions
Pyroclastic Materials• Pyroclastic materials is the name given to
material produced in volcanic eruptions.• Tephra - The fragments ejected during eruptions
range in size from very fine duct and volcanic ash (less than 2 millimeters) to pieces that weigh several tons.
Volcanic Material
The Nature of Volcanic Eruptions
Pyroclastic Materials (Tephra)• Types of pyroclastic material
- Ash and dust—fine, glassy fragments - Pumice—frothy, air-filled lava - Lapilli—walnut-sized particles- Cinders—pea-sized particles
• Particles larger than lapilli- Blocks—hardened lava- Bombs—ejected as hot lava
S.8
Anatomy of a “Typical” Volcano
• A volcano is a mountain formed of lava and/or pyroclastic material.
• A conduit, or pipe, carries gas-rich magma to the surface.
• A crater is the depression at the summit of a volcano or that which is produced by a meteorite impact.
6
Anatomy of a “Typical” Volcano Anatomy of a “Typical” Volcano
Fill in handout.
S.9
Types of Volcanoes
The Nature of Volcanic Eruptions
The three main volcanic types are
shield volcanoescinder conescomposite volcanoes
S.10
Types of Volcanoes
S.11
7
Types of Volcanoes
The Nature of Volcanic Eruptions
Shield VolcanoesShield volcanoes are broad, gently sloping volcanoes built from fluid basaltic or maficlavas.
Shield Volcanoes
Types of Volcanoes
The Nature of Volcanic Eruptions
Cinder ConesCinder cones are small volcanoes built primarily of pyroclastic material ejected from a single vent.
- Steep slope angle - Rather small in size
- Frequently occur in groups
Cinder Cones
8
Types of Volcanoes
The Nature of Volcanic Eruptions
Composite Cones• Composite cones are volcanoes composed of
both lava flows and pyroclastic material. - Large size - Most violent
Composite Cones
Mount St. Helens Before and After the May 18, 1980, Eruption Profiles of Volcanic Landforms
S.12
9
Other Volcanic Landforms
The Nature of Volcanic Eruptions
Calderas• Calderas are large depressions in volcanoes.
• Formed by collapse
• Nearly circular
• Size exceeds one kilometerin diameter
Origin of MagmaGeologists conclude that magma originates when solid rock, located in the crust and upper mantle, partially melts.
Intrusive Igneous Activity
The water trapped in a subducting plate is heated and released to melt the rock above the subducting plate to form volcanic chains within mountain ranges or volcanic island arcs in the ocean.
Types of Igneous Plutons Types of Igneous Landforms
Lava Plateaus - Fluid basaltic lava extruded from crustal fractures called fissures. Volcanic NecksPlutons are intrusive igneous structuresthat result from the cooling and hardening of magma beneath the surface of Earth.
DikesSillsLaccoliths and LopolithsColumnar Basalt
S.13
10
Types of Igneous Plutons
S.14
Batholith
Sill Radiating Dike
11
Volcanic Neck
Shiprock
Caldera
Crater Lake, Oregon(Mt. Mazama 7200 ya)
Lava or Basalt Plateau
Columbia Plateau
Columnar Basalt
Devils Post Pile
Giants Causeway
12
Volcanic HazardsEffusive Eruptions
• Effusive eruptions are characterized by outpourings of lava on to the ground.
Hawaii
S.15a
Fissure Eruption
Heimaey, Iceland
S.15b
Lava Flow - Heimaey, Iceland
• Iceland, January 23,1973.
• Large fissure eruption threatened the town of Vestmannaeyjar.
13
Lava Flow - Heimaey, Iceland• The lava flows caught
the inhabitants by surprise
• Before the eruptionwas over, approximately one-third of the town of Vestmannaeyjer had been destroyed
Lava Flow - Heimaey, Iceland• However, the potential damage was reduced by
spraying seawater onto the advancing lava flows. • This caused them to slow and/or stop, or diverted
them away from the undamaged part of the town.
• Three products from an explosive eruption– Ash Load– Pyroclastic flow– Pyroclastic surge
Explosive Eruptions
Pyroclastic flows on Montserrat, buried the capital city.S.16
• 92,000 Tambora, Indonesia 1815
• 36,000 Krakatau, Indonesia 1883
• 29,000 Mt Pelee, Martinique 1902
• 15,000 Mt Unzen, Japan 1792
Volcanic Fatalities
But, volcanoes cause fewer fatalities than earthquakes, hurricanes and famine.
Courtesy of www.swisseduc.ch
14
Volcanic Hazards• Pyroclastic Flow or Nuee Ardente• Mudflows or Lahars• Pyroclastic Ash fall• Lava flow• Earthquakes• Noxious Gas
Some significant eruptions:• 92,000 Tambora, Indonesia 1815• 36,000 Krakatau, Indonesia 1883• 29,000 Mt Pelee, Martinique 1902• 15,000 Mt Unzen, Japan 1792• 800 killed, 100,000 homeless Mt. Pinatubo, Philippines 1991• 2000+ Vesuvius, destroyed city of Pompeii 79 AD • successful evacuation Montserrat, 1995-6 (near Martinique)• 1,700 Lake Nyos, Cameroon 1986
Volcanic Hazards
S.17
Direct measurements of pyroclastic
flows are extremely
dangerous!!!
Mt. Pinatubo
Pyroclastic Flowor Nuée Ardente
Pyroclastic Flow
• For example, eruption of Vesuvius in 79 AD destroyed the city of Pompeii
15
Pompeii (79AD)
On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.
Pompeii (79AD)Pyroclastic flows of poisonous gas and hot volcanic debris engulfed the cities of Pompeii, Herculaneum and Stabiae suffocating the inhabitants and burying the buildings.
Vesuvius Today
• around 1.5 millionpeople live in the city of Naples alone
• Naples is situated approx. 30 km from Vesuvius
• Pyroclastic flows can flow up to 100 km from source!
Bay of Naples
Vesuvius
Naples
Courtesy of www.swisseduc.ch
Vesuvius remains a hazardous volcano with heavily populated flanks.
An eruption of Mt Peleé produced a pyroclastic flow that destroyed the city of St. Pierre.
before after
Mt Peleé, Martinique (1902)
16
29,000 people died…. Only 1 survived!
Why?
25-year-old Louis-Auguste Cyparis
How do pyroclastic flows cause devastation?
Pyroclastic Flow - Direct Impact
Courtesy of www.swisseduc.chS.18a
Pyroclastic Flow - Burial
S.18b
17
Pyroclastic Flow - Burns
S.18c
Pyroclastic Flow - Lahars• Hot volcanic activity can melt
snow and ice• Melt water picks up rock and
debris• Forms fast flowing, high
energy torrents• Destroys all in its path
S.18d
Pyroclastic Fall - Ash Load• Collapses roofs• Brings down power lines• Kills plants• Contaminates water
supplies• Respiratory hazard for
humans and animals
S.18e
Lava Flow
• It is not just explosive volcanic activity that can be hazardous. Effusive (lava flow) activity is also dangerous.
S.18f
18
Lava Flow
Under Sea Pillow Lava
Exercise 3
Assessing Volcanic Hazards…
on the Caribbean Island of Montserrat
Where is it safe to live?
S.19a
Where is it safe to live?
S.19b
19
So….How do we minimize the risk of
active volcanoes?
1. Volcano Monitoring
Volcano Observatories are set up on all active volcanoes that threaten the human population.
These are designed to monitor and potentially to predict the eruptive behaviour of the volcano in question.
S.20a
1. Volcano Monitoring• Seismicity• Deformation• Gas Output
These three things are the
most important precursors to an
eruption.
S.20a
2. Seismic Activity• Earthquake activity commonly precedes an eruption
– Result of magma pushing up towards the surface– Increase volume of material in the volcano shatters rock– This causes earthquakes (harmonic tremors)
S.20b
20
2. Seismic Activity• Earthquake activity is measured by Seismographs
– Seismographs are stationed on the flanks of the volcano– These record the frequency, duration and intensity of the
earthquakes and report it back to the volcano observatory.
S.20b
3. Deformation Monitoring• “Tiltmeters” are used to measure the deformation
of the volcano– The tiltmeters measure changes in slope as small as one part per
million. A slope change of one part per million is equivalent toraising the end of a board one kilometer long only one millimeter!
S.20c
3. Deformation Monitoring• Tilltmeters tell you when new material enters the magma chamber.
Note the presence of earthquakes in relation to the deformation.
Often it is a combination of events that fore-warns of an eruption.
A
B
S.20c
4. Gas MonitoringCommonly gas output from a volcano increases or changes composition before an eruption.• As magma rises it releases much of its gas content.• This can be measured
S.20d
21
4. Gas Monitoring• Gas samples are collected from fumaroles
and active vents. • Gas levels may also be monitored by remote
sensing techniques
S.20d
Are there other related hazards?
5. Earthquakes
• Large volumes of magma moving through the shallow crust can cause large earthquakes.
• This can lead to building collapse, slope failure and avalanches.
S.20e
5. Earthquakes
Destruction after a volcanic induced earthquake in Japan
S.20e
22
6. Noxious Gas• 1,700 people living in the
valley below Lake Nyos in northwestern Cameroon mysteriously died on the evening of August 26, 1986.
S.20f
6. Noxious Gas• Lake Nyos is a crater lake inside a dormant
volcano.• The lake had become laden with carbon
dioxide gas. • This gas had suddenly bubbled out of the lake
and asphyxiated nearly every living being in the surrounding valley.
S.20f
6. Noxious Gas• A management plan has been
developed to remove gas from the lake to prevent a further tragedy.
• An artificial vent to the lake surface was created with pipe.
• Water is pumped from the bottom of the lake to the surface through the pipe, where it can degas.
S.20f
6. Noxious Gas
S.20f
23
6. Noxious Gas
S.20f
6. Noxious Gas• The Lake Nyos incident was not unique. • Two years earlier, Lake Monoun, 60 miles to
the southeast, released a heavy cloud of toxic gas, killing 37 people.
• A third lake, Lake Kivu, on the Congo-Rwanda border in Central Africa, is also known to act as a reservoir of carbon dioxide and methane, which is a valuable natural gas that is gathered from the lake and used locally.
S.20f
Exercise 4The Ring of Fire !
• Use the list to label the Volcanoes.(use names NOT numbers!)
• Use arrows to show the relative motion along the boundaries of the Ring of Fire.
S.21
Exercise 5
Terminology Review!Complete the worksheet package.
S.22
24
UNIT TEST - Chapters 13-16
S.23
Assignments:Chapter 13 – Plate Tectonics Notes & Vocab √Chapter 14 – Plate Tectonics & Volcanoes Notes & Vocab √Chapter 15 – Plate Tectonics & Earthquakes Notes & VocabChapter 16 – Plate Tectonics & Mountain Building Notes & Vocab
For Review and Test Prep:Go to esc11.weebly.com
• Flashcard Library (home page)• volcano photo review• link to practice quizzes and review PowerPoints• Quizlab – Chapters 13-16 Practice Test
