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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.
Types:
1.Composite Volcanoes (also called strato
volcanoes),
2. Shield Volcanoes (also called shields),
3. Cinder Cones,
4. Spatter Cones, and
5. Complex Volcanoes (also called
compound volcanoes).
Lets take a look at each type and describe them.
1.
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, 1000km2 in surface
area, and 400km3 in volume.
- Between eruptions they are often so quiet they seem extinct.
- 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.
Composite Volcanoes (also called strato volcanoes)
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).
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 volcanoes
Shield volcanoes
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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.
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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.
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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.
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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).
Mauna Loa This volcano is the largest one on earth. It began to form
millions of years ago. The summit crater, called Mokuaweoweo, has
walls that rise to 180 meters!
Mauna Loa emits lava around very 4 years.
- It is an active shield Volcano, 4170 meters tall
Cinder cone
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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.
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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.
Strombolian - when the magma is viscous, the
locked up gas will escape intermittently when
rising to the surface. Often this results in
blocks and bombs which will fall on the
surrounding environment
Cinder cone
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The cones usually grow up in groups and they often
occur on the flanks of strato volcanoes and shield
volcanoes.
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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.
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Cinder cones grow rapidly and soon approach
their maximum size. They rarely exceed 250m in
height and 500m in diameter.
A Few Volcanic Definitions to get you started:
aa (pronounced "ah-ah") Hawaiian word used to describe a
lava flow whose surface is broken into rough angular
fragments composed of broken lava blocks called clinkers.
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A caldera is a volcanic feature formed by the collapse of a
volcano into itself, making it a large, special form of volcanic
crater. The word 'caldera' comes from a Spanish word
meaning "cauldron".
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In volcanology, a lava dome is mound-shaped growth
resulting from the eruption of high-silica lava (usually
rhyolite and/or dacite) from a volcano.
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A lahar is a type of mudflow composed of pyroclastic
material and water that flows down from a volcano,
typically along a river valley. The term 'lahar' originated in
Indonesia.
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Pāhoehoe (Hawaiian English, from Hawaiian, meaning
"smooth, unbroken lava") is basaltic lava that has a
smooth, billowy, or ropy surface. A pāhoehoe flow
typically advances as a series of small lobes and toes
that continually break out from a cooled crust.
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Pillow lava is the rock type typically formed when lava emerges
from an underwater volcanic vent or a lava flow enters the
ocean.
The viscous lava gains a solid crust immediately upon
contact with the water, and this crust cracks and oozes
additional large blobs or "pillows" as more lava emerges from
the advancing flow.
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Pyroclastic rocks or tephra are deposits comprising the entire
range of fragmental products deposited directly by explosive or
effusive (formed by a nonexplosive outpouring of lava)
volcanic eruptions
Three modes of transport can be distinguished: pyroclastic
flow, pyroclastic surge, and pyroclastic fall
A spatter cone is formed of molten lava ejected from a vent
somewhat like taffy.
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Basalt Plateau extensive continental deposits of basaltic
volcanic rock.
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Complex volcano means 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.
A volcano that consists of a complex of two or more vents is
reckoned as a compound or complex volcano.