I. Perspective On Volcanism

• A. Volcanism has occurred throughout geologic time
  
  • 1. Presently concentrated in the Circum-Pacific Belt and across the Mediterranean and through Indonesian
    
  • 2. Miocene volcanism covered 700 sq miles of LA Basin
    
    • a. Ash left from that period causes many modern landslides
      
• B. Volcanism threatens to destroy numerous major cities
  
  • 1. 1. Examples
    
    • a. Popocatepetl - Mexico City
      
    • b. Mt. Vesuvius - Naples
      
    • c. Mt. Merapi - Jogjakarta
      
    • d. Mt. Rainier - Seattle area
      
    • e. Mt. Hood - Portland
      
• C. Huge Populations have grown in Volcanic Areas
  
• D. Volcanoes by state:
  
  • 1. Alaska - 42
    
  • 2. Arizona - 9
    
  • 3. California - 10
    
  • 4. Hawaii - 13
    
  • 5. Idaho - 3
    
  • 6. New Mexico - 10
    
  • 7. Oregon - 22
    
  • 8. South Dakota - 1
    
  • 9. Utah - 2
    
  • 10. Washington - 7
    
  • 11. Wyoming - 2
    

II. How Volcanoes Cause Damage

• A. Lava Flow Eruption
  
  • 1. Generally slow moving and not a threat to cities
    
  • 2. Basaltic lavas are much more fluid than andesitic lavas
    
    • a. Types of basaltic flows
      
  • 1) Pahoehoe lava (resembles a twisted or ropey texture)
    
  • 2) Aa lava (rough, jagged blocky texture)
    
  • 3. Kapoho, Hawaii example
    
    • a. The January 1960 flank eruption followed the December 1959 summit eruption
      
    • b. seismic swarms indicated the eruption was coming
      
    • c. Diversion walls were built but also destroyed by the lava
      
    • d. Kapoho, a farming village, was buried
      
    • e. http://hvo.wr.usgs.gov/kilauea/history/1960Jan13/
      
  • 4. Fissure eruptions and lava plateaus
    
    • a. Fluid basaltic lava extruded from crustal fractures called fissures
      
    • b. e.g., Columbia River Plateau
      
• B. Caldera Collapse
  
  • 1. Believed to be caused by magma evacuating its chamber
    
  • 2. Caldera eruptions in New Zealand could damage cities like Auckland
    
  • 3. Famous (or infamous) collapsed calderas:
    
    • a. Crater Lake, Oregon
      
    • b. Yellowstone, Wyoming
      
    • c. Long Valley Caldera, California
      
    • d. Krakatoa, Indonesia
      
  • 4. Crater Lake
    
    • a. About 6,850 years ago Mount Mazama erupted
      
    • b. Caldera collapsed and produced Crater Lake
      
    • c. Eruption released ~12 cubic miles (50 cubic km) of magma to the surface.
      
      • 1) One of the largest eruptions in the last 10,000 years.
        
  • 5. Yellowstone, Wyoming
    
    • a. A Hot Spot Volcano
      
    • b. Three very large eruptions in the last 2 million years
      
    • c. 2.0, 1.3, and 0.6 million years ago
      
    • d. Still active today
      
  • 6. Long Valley Caldera, California
    
    • a. Volcanic activity began in the area ~3.6 million years ago
      
    • b. Catastrophic eruption ~730,000 years ago
      
      • 1) Bishop Tuff
        
    • c. Mammoth Mountain formed along the southwest rim of Long Valley caldera from 200,000 to 50,000 years ago
      
  • 7. Krakatoa
    
    • a. Inactive for 200 years before 1883
      
    • b. Eruption began in May and climaxed on August 26 & 27
      
      • 1) Lava, ash, and gas erupted
        
      • 2) Ash covered neighboring islands
        
      • 3) Pumice choked the Sunda Strait
        
    • c. Suddenly 10 sq miles collapsed
      
      • 1) A strong Earthquake occurred
        
      • 2) Sound could be heard 3000 miles away
        
      • 3) Tsunami over 100 feet high killed 36,000 people in Java and Sumatra
        
• C. Explosions and Ashflows
  
  • 1. Ashflows are mixtures of hot gas and ash that move very quickly along the ground
    
    • a. Pompeii was destroyed by Ashflows
      
  • 2. Mt St. Helens
    
    • a. Eruption began in late March and climaxed May 18, 1980
      
    • 1) 5.1 magnitude earthquake on nearby fault
      
    • 2) A landslide followed and caused a huge explosion
      
      • a) 0.5 cubic miles of rock fell into Spirit Lake causing mudflows
        
      • b) Ashflow traveling 150 miles/hr traveled 18 miles devastating 215 sq miles (Temperature = 300°C)
        
• D. Ashfall
  
  • 1. Huge areas may be covered by volcanic ash
    
    • a. Crater Lake ash covers the entire Northwest
      
  • 2. Damage to urban areas can be enormous
    
    • a. Crops are destroyed threatening the food supply
      
    • b. Public water contaminated
      
    • c. Buildings collapse under weight of ash
      
    • d. Air travel disrupted
      
• E. Mudflows
  
  • 1. Ways that volcanoes make mudflows
    
    • a. Burn vegetation
      
    • b. Erupt ash
      
    • c. Produce rain
      
    • d. Melt glaciers or displace lakes
      
  • 2. St. Helens example
    
    • a. Mudflow was caused by the displaced Spirit Lake
      
    • b. Mudflow went 60 miles to the Columbia River
      
      • 1) 45 million cubic yards sediment entered Columbia River
        
  • 3. Nevada del Ruiz, Columbia
    
    • a. 2 eruptions on Nov 13, 1985 melted the summit glaciers
      
      • 1) Mudflows travelled in all directions from the summit
        
    • b. Mud traveling 30 mph and 50 feet deep buries Amero 30 miles away
      
      • 1) 25,000 killed
        
  • 4. Mt. Rainier
    
  • a. Mudflows threaten the towns and villages blow this dangerous volcano
    
  • b. Evacuation plans and drills are the key to survival
    
• F. Gas
  
  • 1. Cameroon
    
    • a. August of 1986 Lake Nyos
      
      • 1) 1 km of CO₂ released
        
      • 2) ~1700 people killed up to 26 km away from the lake
        
    • b. August of 1984
      
      • 1) smaller gas burst from Lake Monoun
        
      • 2) 37 people killed
        

I. Perspective On Volcanism | II. How Volcanoes Cause Damage | III. Benefits of Volcanoes | IV. Methods Of Forecasting Volcanic Eruptions | V. Evaluation Of Volcanic Risk In California | VI. The Eruption Of Thera - An Entire Civilization Destroyed | Links | top | Geol 150 Lecture Home

III. Benefits of Volcanoes

• A. Produce great amounts of new land
  
• B. Frequently produce very fertile soils
  
• C. Provide Geothermal Power
  
• D. Recreation
  

I. Perspective On Volcanism | II. How Volcanoes Cause Damage | III. Benefits of Volcanoes | IV. Methods Of Forecasting Volcanic Eruptions | V. Evaluation Of Volcanic Risk In California | VI. The Eruption Of Thera - An Entire Civilization Destroyed | Links | top | Geol 150 Lecture Home

IV. Methods Of Forecasting Volcanic Eruptions

• A. Geophysical methods
  
  • 1. Seismology
    
    • a. Structure of the volcano can be determined
      
    • b. Movement of the magma can be traced
      
  • 2. Gravity Surveys
    
    • a. Can recognize inflation and deflation
      
  • 3. Precise surveying - either conventional or by laser
    
    • a. Reveals changes in shape
      
  • 4. Tiltmeter measurements reveal inflation and deflation
    
  • 5. Heat flow studies
    
• B. Geochemical methods
  
  • 1. The Cl, F, and S composition of hot springs may change before eruptions
    
    • a. Has worked in Japan
      
• C. Geochronology
  • 1. Precise dating may reveal regular repeat intervals
    

I. Perspective On Volcanism | II. How Volcanoes Cause Damage | III. Benefits of Volcanoes | IV. Methods Of Forecasting Volcanic Eruptions | V. Evaluation Of Volcanic Risk In California | VI. The Eruption Of Thera - An Entire Civilization Destroyed | Links | top | Geol 150 Lecture Home

V. Evaluation Of Volcanic Risk In California

• A. Population changes since 1915
  
  • 1. Last violent eruption was Mt Lassen in 1915
    
    • a. California population was 2,800,000
      
  • 2. 1999 population was >34,000,000
    
  • 3. Some of this population has extended into volcanically hazardous areas
    
• B. The 3 Most Dangerous Areas in California
  
  • 1. Mt Shasta especially around Weed on west side - ashflows
    
  • 2. Mt Lassen - mudflows and rock avalanches
    
  • 3. Long Valley - Mammoth Mtn area
    

I. Perspective On Volcanism | II. How Volcanoes Cause Damage | III. Benefits of Volcanoes | IV. Methods Of Forecasting Volcanic Eruptions | V. Evaluation Of Volcanic Risk In California | VI. The Eruption Of Thera - An Entire Civilization Destroyed | Links | top | Geol 150 Lecture Home

VI. The Eruption Of Thera - An Entire Civilization Destroyed

• A. Located in the eastern Mediterranean
  
  • 1. Southern most of Cycladic Islands
    
• B. The Minoan Civilization
  
  • 1. Minoans developed an advanced, maritime-based civilization in the eastern Mediterranean between 2000 and 1450 B.C.
    
  • 2. Minoans were wealthy traders who lived in peace
    
  • 3. Civilization was most developed on Crete
    
    • a. Palaces built at Knossos, Phaestos, and Zakros
      
    • b. Aqueducts and sewage systems
      
    • c. Good ports
      
    • d. Advanced art in painting and ceramics
      
  • 4. Thera or the Minoans are probably Plato's lost Atlantis
    
    • a. From Plato's Timaeus - "But afterwards there occurred violent earthquakes and floods and in a single day and night of misfortune the island of Atlantis disappeared in the depth of the sea. For which reason the sea in those parts is impassable because there is a shoal of mud in the way."
      
• C. The Eruptions
  
  • 1. The first historic eruption occurred in 1500 B.C.
    
    • a. Thera was evacuated permanently
      
  • 2. Caldera collapse occurred on 1450 B. C.
    
    • a. 32 sq miles collapsed into the Mediterranean
      
    • b. A tsunami spread through the Mediterranean hitting Crete perhaps 300 feet high
      
    • c. Earthquakes preceded and followed the eruption
      
    • d. Ash over 1 foot deep destroyed crops on Crete - starvation followed
      
    • e. All Minoan population centers were destroyed simultaneously
      
  • 3. The Egyptians described the eruption - "For 9 days there was no exit from the palace and no one could see the face of his fellow. It is inconceivable what has happened in the land - to its whole extent confusion and terrible noise of tumult. Oh that the Earth would cease from noise. The towns are destroyed. Upper Egypt suffered devastation. Blood everywhere. Pestilence throughout the whole country. Men no longer sail to Byblos. What shall we do for cedar for our mummies and for the oils with which the chiefs are embalmed as far as the country of the Cretans? They come no more. The sun is covered and does not shine to the sight of men. Life is no longer possible when the sun is concealed behind the clouds. Ra has turned his face from mankind. If only it would shine, even for one hour! No one knows when it is midday; One's shadow is not discernible. The sun in the heavens resembles the moon."
    
• D. The Mycenaeans rose to rule the Mediterranean
  
  • 1. Trade collapsed as piracy took over
    
  • 2. Agamemnon led a prolonged war against Troy around 1250 B.C.
    
    • a. Mycennaean resources were greatly depleted.
      
    • b. Agememnon was murdered by his wife upon return to Mycenae
      
• E. Dorian Barbarians conquered the Mycenaeans around 1100 B.C.
  
  • 1. Greece retreated to Stone Age conditions similar to the year 3000 B.C.
    
    • a. The Archean period began
      

I. Perspective On Volcanism | II. How Volcanoes Cause Damage | III. Benefits of Volcanoes | IV. Methods Of Forecasting Volcanic Eruptions | V. Evaluation Of Volcanic Risk In California | VI. The Eruption Of Thera - An Entire Civilization Destroyed | Links | top | Geol 150 Lecture Home