G 208 Lecture Notes 05/28/2005

 

  • Principle methods of volcano monitoring

1)      Gas pressure

2)      Movement of magma (formed from depth that works its way up in the fractures)

 

  • For better, process-based forces we need to forecast gas

 

  • Gas leaks: lava domes

 

·        Viscous magma + slow ascent to surface

-         Pre-eruption gas leakage

-         Low explosive potential

 

·        Effusive Eruptions

-         Low viscosity magma

-         Gas not very mobile and can’t escape easily

-         IF ALSO rapid ascent,

-         High gas content persists to near surface

-         Large potential expansion

 

  • Two modes of conduit

1)      Closed tight

            -     Dangerous

            -     No convection in the conduit; incoming gas is stored

            -     Infrequent large explosive eruptions

            -     Strong eruption precursor

            -     Ample warning

2)      Open, leaky

               -     Difficult to give warnings

 

  • Two ways earthquakes associated with volcanoes

1)      Volcanic earthquakes

            -     Due to breaking of rocks as magma moves

2)      Harmonic tremors (aka volcanic tremor)

               -     Are uniquely associated with volcanoes

               -     Consist of more or less continuous ground vibration

               -     There can be swarms of volcanic quakes associated with movements of magma

               -     Are nearly always present during a volcano eruption

 

  • Swarms of earthquakes

-         Are not a reliable prediction of volcanic eruption

 

  • Biggest uncertainty

   -     The degrees to which magma is trapping gas

   -     Ex: how tight and leaky volcano           

 

  • Big eruptions are generally easier to forecast with lend times of days to months
  • Small eruptions are tougher to forecast

 

  • Long Valley caldera

-         Has been explosive in prehistoric past

-         Due to hotspots not plate tectonics

-         Volcanologists predicted the possibility of an eruption due to ground uplift

-         No eruption occurred and lots of lawsuits

 

·        Mount St. Helens

-         April 2, 1980: EQs swarms and harmonic tremor indicating magma is moving around

-         May 18, 1980: Catastrophic and huge eruption

-         May 25, 1980: large EQs

-         Trees died from the released of carbon dioxide (CO2)

 

  • Tiltmeters and EQs swarms

-         Tools used but not very reliable

 

  • Origin of Earth’s atmosphere

-         Putting together from gas and cloud

-         H, He, C, N, O, Ne, Mg, Si, S, Fe

 

  • Depends on two things

1)      Gravity of planet          

2)      Surface temperature

 

  • When build planet volcanisms; melt rocks
  • Earth came in with comets that made with lots of water and got a lot of sulfur

 

  • Coming out from volcano

-         H2O: water vapor

-         CO2

-         N2: nitrogen and sulfur

-         H2

 

  • The atmosphere of Venus and Mars

-         Approximately 95% of carbon dioxide and 3% of nitrogen

1)      Venus

            -     Close enough to sun; water vapors

2)      Mars

               -     Probably chemical reaction frozen under ground

 

  • Earth

-         Mostly carbonate rocks

-         Nitrogen from plants that is about 70%

 

  • Subduction volcanoes

-         Recycle the CO2

-         Weathering remove CO2; volcanoes put it back

 

  •  CO2

-     Can poison things

-     Green house gas (water vapors)

-     Raises to comfortable temperature

-     Heat + sun = electromagnetic waves

      (Short, visible light heat)

 

  • Volcanoes

-         Help to regulate CO2

-         We don’t want too little or too much but just right

-         Tend to make short term effect on climate

-         Ex: Krakatau

-         Dust blocks sunlight which cools the earth and bends sunlight

-         Gas emitted: CO2 combine with water vapor to make carbonic acid

-         Trees sometimes are killed by sulfuric and carbonic acid

-         Other gases in volcanic eruptions are toxic that can kill vegetations