The diagram shows the several stages in the formation of a volcanic island and how it eventually becomes an underwater reef.
In the first two stages (‘pillow/preshield’ and ‘Hyaloclastic/protoshield’ stages) a mountain begins to form under the surface of the sea. Once the mountain starts peeking over the surface comes the ‘explosive’ phase hydro-explosions occur, layering the mountain with a cone of ash. Over time, this ash cone is covered by what appears to be sediment(Shield Stage), which is once again, over time covered by cinder cones(Postshield Stage).
This shield of cinder cones and sediment erodes over time, giving an opportunity for coral reefs to from. If the volcanic activity is rejuvenated, lava flows out into the sea, allowing for the formation of more coral reefs. If a volcanic eruption takes place, the top of the mountain becomes table-land which completely taken over by corals. This is the ‘coral atoll’ stage. Over time, the weight of the reef compresses the surface further down into the sea forming a fully underwater coral reef. This is called the Guyot stage.
The diagram
shows
the several
stages
in the formation of a volcanic island and how it
eventually
becomes an underwater reef.
In the
first
two
stages
(‘pillow/
preshield
’ and ‘
Hyaloclastic
/
protoshield
’
stages)
a
mountain
begins
to form under the surface of the sea. Once the
mountain
starts
peeking
over
the surface
comes
the ‘explosive’ phase hydro-explosions occur, layering the
mountain
with a cone of ash.
Over
time
, this ash cone
is covered
by what appears to be sediment(Shield
Stage)
, which is once again,
over
time
covered by cinder cones(
Postshield
Stage).
This shield of cinder cones and sediment erodes
over
time
, giving an opportunity for
coral
reefs
to from. If the volcanic activity
is rejuvenated
, lava flows out into the sea, allowing for the formation of more
coral
reefs
. If a volcanic eruption takes place, the top of the
mountain
becomes table-land which completely taken
over
by corals. This is the
‘coral
atoll’
stage
.
Over
time
, the weight of the
reef
compresses the surface
further
down into the sea forming a
fully
underwater
coral
reef
. This
is called
the
Guyot
stage
.