Lava flows don't typically cause loss of life, but lava can
              pose a threat to human structures and agricultural fields
              that lie in their paths.

              Flows can sometimes be diverted from populated areas. 
  

         2.  ASH FALLS

              The largest sized tephra (blocks and bombs) fall closest
              to a volcano, but ash is blasted high into the sky and can
              travel long distances before settling to the ground.  Ash is
              dangerous to breathe and can cause damage to engines or
              machines, including aircraft.
 

              Large eruption clouds send ash high into the stratosphere,
              the upper atmosphere where particles remain suspended
              for long time periods.  Ash in the stratosphere reduces the
              solar radiation that reaches the  earth's surface, which then
              results in lower temperatures.

              The 1815 eruption of Mount Tambora in Indonesia resulted
              in three years of abnormally low temperatures in northern
              Europe and the eastern United States, causing the so-called
              "year without a summer" in 1816. 

         3.  ASH FLOWS

              Ash flows (also known as pyroclastic flows or the French
              term nuees ardentes) are fast-moving clouds of volcanic
              gas and pyroclastic debris.  These intensely hot and very
              poisonous clouds destroy everything in their paths. 

              The most famous ash flow occurred in 1902, when Mount
              Pelee in Martinique erupted, killing 30,000 people.

        4.  DEBRIS FLOWS 

              Debris flows (also known as lahars, an Indonesian word)
              are fast-moving flows composed of water and pyroclastic
              debris.  These flows are initiated when rain or snowmelt
              saturates pyroclastic debris ejected during an eruption. 

              Example:  1985 eruption of Nevado del Ruiz in Colombia.

 

         5.  TSUNAMIS

               Volcanic eruptions, like earthquakes, can generate giant
               sea waves ("tidal waves") if they occur in the ocean. One
               of the more destructive tsunamis was caused by the 1883
               eruption of Krakatoa in Indonesia (36,000 died).

         6.  VOLCANIC GASES

              Volcanic gases have various harmful effects, including the
              formation of sulfuric acid (called "VOG"), the destruction of
              atmospheric ozone, and the death of surface vegetation.