Historical eruptions.

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HISTORICAL ERUPTIONS:

   No. Of Recorded Eruptions:  45 since 1616

   Latest Eruption:  02 February 1993 (Strombolian & Vulcanian types)

   Most Destructive Eruption:  01 February 1814; 1,200 people perished due to lahars

   Eruption Types:

      Strombolian - quiet emission of lava (e.g. 1978, 1st phase of 1984 eruption)

      Vulcanian - violent explosions and eruptions of pyroclastic flows 

                  (E.g. 1st phase of 1968 eruption, 2nd phase of 1984 eruption)

      Plinian - extremely violent explosions with continuous sustained 

             Ejection of pyroclasts (e.g. 1814 eruption)

   Precursors to Eruptions:  

      a) Increase in seismicity level (Background: 0-10 volcanic quakes per day)

      b) Ground tilt due to magma intrusion 

      c) Change in colour of steam emission from white to grey due to entrained ash 

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      c) Increase in the volume of steam emission 

      d) Crater glow due to presence of magma at or near the crater

      e) Rumbling sounds because of gas explosion

      f) Rock falls and landslides caused by the rising magma and unstable 

         Rocks at or near the summit

      g) Fissuring due to pressure exerted by the rising magma (rarely observed)

   Phenomena Associated with Eruptions:

       Air fall tephra (ballistic fragments, ashfalls)

       Pyroclastic flows

       Lava flows

       Lahars

MONITORING TECHNIQUES:

        Monitoring Methods:

                A.  Geophysical Method 

                    Seismic monitoring - telemetered ...

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