Composite volcanoes, also called stratovolcanoes, are formed from layers of lava and rock fragments ejected from a central vent. They often form tall, steep conical peaks over 1000 meters high and can erupt explosively when viscous magma builds up pressure in the vent. Stratovolcanoes display a variety of shapes including concave, pyramidal, and those with multiple summits. Shield volcanoes are broad, gently sloping cones produced by fluid basaltic lava flows over a large area from a central vent. Cinder cones are small, steep hills formed from accumulation of ejected volcanic cinder around a vent.

3. Composite volcanoes, also called Strato volcanoes, they are
formed by alternating layers of lava and rock fragments. This
is the reason they are called composite.
Strato-volcanoes often form impressive, snow-capped peaks
which are often exceeding 2500m in height, 1000sq.km in
surface, and 400km3 in volume.
Between eruptions they are often so quiet they seem
extinct. To witness the start of a great eruption requires luck
or very careful surveillance.
Composite volcanoes usually erupt in an explosive way. This
is usually caused by viscous magma. When very viscous magma
rises to the surface, it usually clogs the crater pipe, and gas in
the crater pipe gets locked up. Therefore, the pressure will
increase resulting in an explosive eruption.
Although Strato-volcanoes are usually large and conical, we
can distinguish different shapes of them: concave , pyramidal,
convex-concave, helmet-shaped , collapse caldera, nested ,
multiple summits, elongated along a fissure .

4. Different Shapes of Composite Volcanoes.

6. Shield volcanoes are huge in
size. They are built by many layers
of runny lava flows. Lava spills out of
a central vent or group of vents. A
broad shaped, gently sloping cone is
formed. This is caused by the very
fluid, basaltic lava which can't be
piled up into steep mounds.

7. Shield volcanoes may be produced by hot spots
which lay far away from the edges of tectonic
plates. Shields also occur along the mid-oceanic
ridge, where sea-floor spreading is in progress
and along subduction related volcanic arcs.
The eruptions of shield volcanoes are
characterized by low-explosivity lava-fountaining
that forms cinder cones and spatter cones at the
vent. Famous shield volcanoes can be found for
example in Hawaii.

9. A Cinder cone is a steep conical hill formed above a
vent. Cinder cones are among the most common volcanic
landforms found in the world. They aren't famous as their
eruptions usually don't cause any loss of life. Cinder cones
are chiefly formed by Strombolian eruptions. The cones
usually grow up in groups and they often occur on the flanks
of Strato volcanoes and shield volcanoes.
Cinder cones are built from lava fragments called
cinders. The lava fragments are ejected from a single vent
and accumulate around the vent when they fall back to
earth.
Cinder cones grow rapidly and soon approach their
maximum size. They rarely exceed 250m in height and
500m in diameter.

10. The shape of a cinder cone can be
modified during its (short)
life. When the position of the vent
alters, aligned, twin or secant cones
develop. Nested, buried or
breached cones are formed when
the power of the eruption varies.

12. When hot erupting lava contains just
enough explosive gas to prevent the
formation of a lava flow, but not enough
to shatter it into small fragments the
lava is torn by expanding gases into fluid
hot clots, ranging in size from 1cm to
50cm across, called spatter.
When the spatter falls back to Earth
the clots weld themselves together and
solidify forming steep-sided
accumulations. These accumulations
focused on an individual vent are called
spatter cones.

14. Different shapes of Spatter Cones

15. Complex Volcanoes can also be called as
compound volcanoes
In fact all volcanoes could be complex
volcanoes since all of them are made up
of multiple flows, ash
layers, domes, cones, etc. in varying
amounts.
However, when we call a volcano a
complex volcano it is because we mean
the "system" of those volcanoes is not
"simple". Caldera complexes for instance
have often got a large caldera with many
subsidiary vents and deposits, some of
which could be considered "volcanoes" in
their own right.
Frankly speaking, a volcano that
consists of a complex of two or more
vents is reckoned as a compound or
complex volcano.

17. These are all different types of Complex Volcanoes

18. How does Volcanoes erupt ???????
An eruption begins when pressure on a
magma chamber forces magma up
through the conduit and out the
volcano's vents. When the magma
chamber has been completely filled, the
type of eruption partly depends on the
amount of gases and silica in the
magma. The amount of silica determines
how sticky (level of viscosity) the magma
is and water provides the explosive
potential of steam.

19. 1. low water, low silica - runny lava flows
(not viscous)

20. 2. low water, high silica (very viscous) - pasty lava - often
building domes.

21. 3. high water, low silica(not viscous) - fountain of runny
lava

22. 4. high water, high silica (very viscous) - explosion