What do you think about when you think
about volcanoes? Do you think about
explosive eruptions or slow lava flows?
There is a lot more to know about
volcanoes and volcanic eruptions. First,
let's talk about what a volcano is. A
volcano is defined as a fissure that
develops in the Earth's crust as magma
moves forcefully towards the Earth's
surface. Volcanoes are constructed as
magma accumulates around the fissure
opening. Volcanoes are normally
classified into Shields, Cinder Cones and
Stratovolcanoes. Shield volcanoes are
large, broad, domed structures formed by
layers of lava that quietly flow out of
the vent and accumulate over time. Mauna
Loa in Hawaii is a good example. A second
type is smaller and called a Cinder Cone.
These are made of a volcanic rock called
scoria which are small bits of lava
ejected by volcanic gases that hardened
in midair.
Because scoria is never thrown very far
from the vent, cinder cones are steep. The
most beautiful volcanoes are large, steep
stratovolcanoes. These are composite
volcanoes that are formed out of
alternating layers of scoria, like
pyroclastic material and lava. These
constructions are steep and strong and
reach great heights.
Fujiyama in Japan is a famous example.
These are the three types of volcanoes
that you may be familiar with, but did
you know that most volcanoes erupt
deep under the sea? These deep-sea
volcanoes can't easily be classified as
Shield, Cinder Cones, or Stratovolcanoes.
So what are they? This is a map of the
world's ocean ridge system that spans
more than 70,000 kilometers in total.
These spreading ridges are located at
divergent margins and are defined as a
nearly continuous range of underwater
volcanic mountains. The mid-atlantic
ridge is arguably the most famous
example of a spreading ocean ridge. These
ridges are essentially one long volcano
that is neither Shield, Composite, or
Cinder Cone. Because volcanic eruptions
underwater are not explosive they
generally create a different kind of
lava known as pillow lava. Pillow lavas
are distinctly tube shaped and are
indicative of a submarine volcanic
eruption. The volcanic processes found at
mid-ocean ridges
and the way that these volcanoes form
are different than any of the three
traditional types of volcanoes. What do
you think we should call these submarine
volcanoes? As you can see there is so
much to learn about them especially
those hidden deep in the ocean.
 
