Pyroclastics
 Pyroclastics or tephra is a general term for
all sizes of particles ejected into the air during volcanic eruptions.
Includes particles as tiny as volcanic ash and as large
as bombs and blocks.
The image at left shows a very close-up
view of volcanic ash. Each one of the ash particles in
this image is smaller than a single pixel on your computer screen! These
ash particles are pumice, volcanic glass that is full
of gas bubbles. The bubbles, called vesicles, form as
gas bubbled out from molten rock that spewed out during a huge eruption
of Brokeoff Mountain in Lassen Volcanic National Park.
The chart on the right shows the names we use to describe different
sizes of tephra. Bombs and blocks can be enormous! Some of the blocks
thrown out of the Woods Mountains volcanic center in Mojave National Preserve
are 15 meters across!
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