Geography Reference
In-Depth Information
The big blast
Avolcaniceruptionisperhapsnature'smostspectacularshow.Insomecasesitconsistsoflava“foun-
tains” and flows. More commonly, however, the event is a big blast accompanied by massive emis-
sions of steam and hot rock particles of all sizes, rather than rivers of lava.
The power of eruptions is sometimes equated to many atomic bombs. Obviously, nobody wants to
be around a volcano when it goes BOOM! But few people tend to live in immediate blast areas, so
BOOM!
per se
is not the big thing you may think, at least in terms of immediate human casualties. In
that regard, two other side effects are of greater importance: ash and lahar.
Making an ash of itself
When explosive volcanic eruptions occur, gazillions of tons of ash (tiny rock particles) are thrown
into the air as a humongous, dense, and potentially suffocating cloud. This is shown in Figure 6-9.
Having weight, these particles eventually fall to earth over a wide area, coating crops, covering roads
and houses, and potentially causing severe (and sometimes fatal) breathing problems for people and
animals. The eruption of Mt. St. Helens provides an excellent case study of the possibilities (see the
“A mountain blows its top” sidebar later in the chapter).
Figure 6-9:
A
photo-graph of a
volcano in erup-
tion.
Lahars
