Volcanoes and Volcanic Landforms

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THE ROCK CYCLE
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VOLCANISM
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I. Introduction

• From Roman god of fire, Vulcan

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I. Introduction

• From Roman god of fire, Vulcan
• What is a volcano?
• A conical mountain formed around a vent where
  lava, pyroclastic materials, and gases are
  erupted.

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I. Introduction

• B. Volcanic activity
• Active
• Dormant
• Extinct

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B. Volcanic Activity

• 1. Active volcanoes
• activity in the last few centuries
• Ex Vesuvius, 79 A.D.
• (50 times in 2000 yr)
• Ex Mt. St. Helens (1980)

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B. Volcanic Activity

• 2. Dormant volcanoes
• quiet for the last hundred to thousands of
  years, but still have potential to erupt.
• Mt. Rainier

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B. Volcanic Activity

• 3. Extinct volcanoes
• No eruption in historical times
• No signs of erupting again

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Introduction C. Volcano Distribution

• Most volcanoes occur in one of three areas
• Circum-Pacific (i.e. The Ring of Fire)
• 60
• Mediterranean
• 20
• Spreading centers
• 10 15

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Volcano Distribution
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II. Volcanic materials

• Three types of material expelled from volcanoes

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Volcanic materials

• A. Lava (the liquid)
• Molten rock

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Volcanic materials

• A. Lava
• Molten rock
• Si affects viscosity

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II. Volcanic materials

• A. Lava
• 1) Pahoehoe lava
• Basaltic lava
• Low viscosity

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II. Volcanic materials

• A. Lava
• 1) Pahoehoe lava
• Basaltic lava
• Low viscosity
• Cools moderately slowly
• Ropelike appearance

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II. Volcanic materials

• A. Lava
• 2) Aa lava (pronounced aa-aa)
• Basaltic lava
• Higher viscosity
• Solidifies while flowing
• Angular pieces

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II. Volcanic materials

• A. Lava
• 3) Pillow lavas
• Lava extruded underwater
• Cools and contracts
• Spherical masses
• Ocean floor

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II. Volcanic materials

• A. Lava (the liquid)
• B. Ash and pyroclastic material (the solid)
• Airborne material ejected by a volcano
• Classified based on size

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B. Ash and pyroclastic material (the solid)

• Volcanic ash
• Fine ash - lt0.06mm
• Coarse ash 0.06mm to 2mm
• Composition rock, mineral, and volcanic glass

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B. Ash and pyroclastic material (the solid)

• Cinders
• 2 mm and 64 mm
• Composition - same as ash
• Hazardous when falling

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B. Ash and pyroclastic material (the solid)

• C) Bombs
• Larger than 64mm
• Molten rock solidifies in the air
• Shapes vary

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II. Volcanic materials

• C. Volcanic gases (the gases)
• Volatiles
• H2S Hydrogen sulfide
• H2O Water vapor
• SO2 Sulfides
• CO2 Carbon dioxide
• N2 Nitrogen
• HCl Hydrochloric Acid
• Significance?

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II. Volcanic materials

• A) Determines violence of an eruption
• High gas violent eruptions
• Violent eruptions felsic magmas
• High viscosity magma traps gas
• Expansion is prevented, pressure builds

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II. Volcanic materials

• B) Effects on global climate
• CO2 Greenhouse gas
• SO2 Blocks sunlight

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II. Volcanic materials

• Hazards to humans
• Clouds of CO2 get released
• Travels across the ground

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III. Volcanic Landforms
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III. Volcanic Landforms

• An erupting volcano will produce a number of
  distinct landforms including
• A. Volcanic cones
• B. Flood basalts
• C. Calderas

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A. Volcanic cones

• Three types of volcanic cones

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A. Volcanic cones

• 1) Shield volcanoes
• Multiple layers of basaltic lava
• Shallow sides due to magmas low viscosity
• Gentle eruptions

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A. Volcanic cones

• 1) Shield volcanoes
• Tall volcanoes 3 or 4 miles tall
• Wide base Diameter of ten of miles

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A. Volcanic cones

• Mauna Loa volcano, Hawaii

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A. Volcanic cones

• 2) Cinder cones
• Smallest volcanic cone
• Layered ash and cinders
• Ex El Paricutin

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A. Volcanic cones

• 2) Cinder cones
• Short, narrow cone,
• Steep sides
• Violent eruptions

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A. Volcanic cones

• Lassen National
• Monument, CA

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A. Volcanic cones

• 3) Composite or stratovolcanoes
• Layered ash, lava, and mud
• Intermediate to felsic lava
• Steep sides, due to lavas high viscosity

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A. Volcanic cones

• 3) Composite or stratovolcanoes
• Tall volcanoes 1 to 2 miles high
• Violent eruptions

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A. Volcanic cones

• Mt. St. Helens,
• WA

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III. Volcanic Landforms B) Flood basalts

• Large outpourings of basaltic lava
• Multiple, quiet eruptions
• Lava plateau

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B) Flood basalts

• A portion of the Columbia Flood Basalts in WA

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III. Volcanic Landforms

• C) Calderas
• Large depressions (gt 1km) from violent eruptions
• Ugashik Caldera, AK

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C) CalderasTwo methods of formation

• Method 1
• Volcano rapidly empties its magma chamber, and
  support is lost

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C) Calderas

• Method 1 (cont.)
• Overlying material collapses into magma chamber
• Caldera forms

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C) Calderas

• Ex Crater Lake,
• OR

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C) CalderasTwo methods of formation

• Method 2
• Volcano blows its top,
• leaving behind a void
• Inside the cone.

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C) CalderasTwo methods of formation

• Method 2
• Volcano blows its top,
• leaving behind a void
• Inside the cone.

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IV. Volcanic hazards
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IV. Volcanic hazards

• Lahars (hot mud flows)

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IV. Volcanic hazards

• Lahars
• Sources of water
• Melting ice caps
• Excess rainfall

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IV. Volcanic hazards

• B) Nuee Ardentes (Glowing Ash flows)
• Clouds of dense gas and debris
• French for glowing cloud
• High speeds and high temperatures

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IV. Volcanic hazards

• How does a Nuee Ardente form?
• Volcano erupts
• Hot debris rises
• Gravity takes over

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IV. Volcanic hazards

• How does a Nuee Ardente form?(contd)
• Debris descends rapidly (200 mph)
• Flows down mountain slopes
• Travel up to 80 miles

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IV. Volcanic hazards

• C) Tsunamis
• Wave generated by volcanic explosion
• Japanese for harbor wave

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IV. Volcanic hazards

• Tsunamis are extremely hazardous
• Travel vast distances
• Strike with short notice
• Krakatoa (1883) - 36,000 people died

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IV. Volcanic hazards

• D) Lava flows
• Least dangerous
• Lava flows slowly (lt10 mph)
• Dangerous to property

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V. Predicting Eruptions

• Why try to predict eruptions?
• Minimize damage
• Minimize loss of life
• Four ways to predict an eruption

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V. Predicting Eruptions

• 1) Harmonic tremors
• Small earthquakes
• From moving magma
• Last for hours

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V. Predicting Eruptions

• 2) Increased gas emissions
• CO2
• SO2
• H2S
• Large tracts of healthy forests die off

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V. Predicting Eruptions

• 3) Changes in mountain shape
• Pressure from the magma deforms the mountain
• Detected by tiltmeters

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V. Predicting Eruptions

• Tiltmeter
• Tiltmeter measures ground tilt
• Stable ground zero tilt
• Change from zero indicates shape change

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V. Predicting Eruptions

• Mt. St. Helens and the orange line

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V. Predicting Eruptions

• 4) Observe material from past eruptions
• Geologists map out past
• Lahars
• Lava flows
• Count number of past eruptions
• Date each eruption
• Calculate periodicity

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VI. Benefits of Volcanoes

• Benefits of volcanoes
• Soils
• Energy from heat
• Rock (Pumice)
• Gases for industry