Download Types of Volcanoes

TYPES OF VOLCANOES
Volcanologists have classified volcanoes into groups based on the shape of the volcano, the materials
they are built of, and the way the volcano erupts.
The groups are:
Composite Volcanoes (also called strato volcanoes),
Shield Volcanoes (also called shields),
Cinder Cones,
Spatter Cones, and
Complex Volcanoes (also called compound volcanoes).
COMPOSITE VOLCANOES
(Fig. 2.4) Composite Volcano.
Composite volcanoes, also called strato volcanoes, 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.
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 craterpipe, and gas in the craterpipe
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 (like Agua), pyramidal (like Stromboli), convex-concave (like Vesuvius), helmet-shaped (like
Mount Rainier), collapse caldera (like Graciosa), nested (like El Piton in Teide), multiple summits (like
Shasta), elongated along a fissure (like Hekla).
(Fig. 2.5) Different Shapes of Composite Volcanoes.
Strato-volcanoes are constructed along subduction zones. Examples of composite volcanoes include
Mount Hood, Mount Rainier, Mount Shasta, Mount Fugi, Mount Mayon, and Vesuvius.
SHIELD VOLCANO
(Fig.2.6) Shield Volcano.
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.
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 (e.g.
Mauna Loa and Kilauea).
CINDER CONE VOLCANO
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.
(Fig.2.7) Cinder Cone.
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.
A great example of a cinder cone is Paricutín in Mexico. It was born in February 20, 1943 in a corn field
and grew to 300 feet in 5 days.
SPATTER CONE VOLCANO
(Fig.2.8) Spatter Cone.
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.
COMPLEX 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.