Geology 309 - Lecture 5

Volcanic Activity - types & particles

I. Classification

A. Effusive vs. explosive
B. Conventional vs. hydrovolcanic

Hydrovolcanic eruptions: Water and volcanism together. Very explosive!

1. Phreatic - interaction with groundwater
2. Surtseyan
Classic example: Surtsey, Iceland

3. Phreatoplinian - silicic
4. Sub-glacial eruptions - includes jokulhlaups

C. Central vent vs. fissure
D. Polygenetic vs. monogenetic

II. Size

• Magnitude
• Dispersive power
• Intensity

III. Volcanic particles - volcaniclastic

A. Pyroclastic
B. Hydroclastic

Tephra with no size implied, only gas content and form:
• Pumice
  
• Reticulite
  
• Scoria
  
• Pele's tears
  
• Pele's hair
  
• Spatter
Size-dependent tephra terminology:

• Ash - <2mm in diameter (Tuff)
  
  
• Lapilli - 2-64 mm in diameter (Lapillistone, Lapilli Tuff if mixed with ash)
  
  
• Bombs or blocks - >64 mm in diameter (Breccia)
  • ribbon bombs
  • spindle bombs
  • cow-dung bombs
  • spheroidal bombs
  • bread-crust bombs
  
  

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