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VOLCANOESCLIL: lesson 2
5D 2016/17
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Recap and Warmer
Try to remember at least 5 words you looked
for during the last lesson.
What did your classmates assert about Earth
science?
Do you realise how much in your life depends
on raw materials? Try to use the handouts to
give an example.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
CLIL: learning objectives
Describe the structure of a generic volcano
Describe the types of volcanoes
Describe the different types of volcanic
eruptions
Describe how volcanoes form
Describe where volcanoes occur and why
Describe the main active volcanoes in the
world
Describe the main active Italian volcanoes
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Volcano: what’s exactly?
Volcano
A vent (we’d call it a rupture) in Earth's surface through which molten rock and gases escape. The term also refers to deposits of ash and lava that accumulate around this vent.
http://geology.com/dictionary/glo
ssary-v.shtml
http://www.universetoday.com/29
125/parts-of-a-volcano/
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6
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5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Students at work!
Match the numbers with the correct name and definition (you could also draw the volcano).
There’re more definitions than numbers on the picture, try to collocate them.
Make a list of the verbs describing the actions.
You have fiftteen minutes.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Scaffolding
Social – constructivist learning in
essence focuses on interactive,
mediated and student-led
learning. This kind of scenario
requires social interaction
between learners and teachers
and scaffolded (supported)
learning by someone or
something more expert –
teacher, other learners or
resources
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
There are many types of volcanic structures
And they are a consequence of the magma and lava composition.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
1. Fissure vent: few meters
wide, many kilometers long.
2. Fluid basaltic lava or, it’s the
same, mafic lava (even if
not always).
3. Absence of esplosive
activity.
4. Basaltic plateaux. (there’s
no mountain).
1. Central vent
2. Fluid basaltic lava
3. Gentle lava eruptions with
little explosive activity and
spectacular fire fountains
4. Broad, low-angled cone
SHIELD VOLCANO
FISSURE VOLCANO
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
1. Central vent
2. Lava composition is highly
variable; alternating mafic
to felsic lavas.
3. Eruptions change widely because it is related to
magma composition
(viscosity and gases) and to
the amount of water. They
can be from slightly to
highly explosive.
4. Gentle lower slopes, but
steep upper slopes;
concave upward; small
summit crater.
STRATOVULCANO or
COMPOSITE CONE
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Students at work! 2
Find out the parameters that define magma types.
Make a list of the unknown words.
Solve the crosswords (homework).
You have fifteen minutes.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
MAGMA TYPES
They are defined by composition, viscosity, temperature and gas content.
COMPOSITION: silica content (SiO2), or better the sulfate ion
content, define magma types: from mafic magmas (relatively low
silica and high Fe and Mg contents) to felsic magmas, (relatively
high silica and low Fe and Mg contents).
VISCOSITY: the ability of a substance to resist flow. It depends on
temperature and silica content: decreases when temperature
grows, increases when silica content grows.
GAS CONTENT: size and distribution of the bubbles influence the viscosity and highly cause the explosiveness of the eruption.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
SiO2
MAGMA
TYPE
TEMPERATU
RE
(centigrade)
VISCOSITYGAS
CONTENT
ERUPTION
STYLE
~50% mafic ~1100 low low nonexplosive
~60% intermediate ~1000 intermediate intermediate intermediate
~70% felsic ~800 high high explosive
From MAGMA TYPES to ERUPTION STYLES
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
ERUPTION STYLES
Eruption styles from nonexplosive to explosive
Fissure eruptions or Icelandic eruptions
Hawaiian eruptions
Strombolian eruptions
Vulcanian eruptions
Plinian eruptions
Hydrovulcanic eruptions
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Fissure eruptions or Icelandic eruptions
They are generated from sites along a linear fracture.Regional fracture systems can appear where the Earth'scrust is broken and pulled apart by tensional forces(divergent plate margins). Because Iceland is the subaerialextension of the Mid-Atlantic Ridge, it is one of the world'smost active sites for basaltic fissure eruptions.
As fluid, gas-poor basaltic magma rises up through a fissure,it is extruded at the surface as a wall of incandescent, liquid-to-plastic fragments known as a curtain of fire.
It generates a basaltic plateaux.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Hawaiian eruptionsHawaiian eruptions are the calmest of the eruption types.They are characterized by the effusive emission of highlyfluid basalt lavas with low gas contents. The relative volumeof ejected pyroclastic material is less than that of all othereruption types. The hallmark of Hawaiian eruptions is steadylava fountaining and the production of thin lava flows thateventually build up into large, broad shield volcanoes.Eruptions are common in central vents near the summit ofshield volcanoes, and along fissures radiating outward fromthe summit area. Lava advances downslope away fromtheir source vents in lava channels and lava tubes.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Explosive eruptionsExplosive eruptions occur where cooler, more viscous magmas try to
reach the surface. Magma surface can harden, making a cap so
dissolved gases cannot escape easily, so pressure may build up until
gas explosions blast rock and lava fragments into the air.
The greater the explosivity the greater the amount of fragmentation.
Individual eruptive fragments are called pyroclasts ("fire fragments")
while Tephra (Greek, for ash) is a generic term for any airborne
pyroclastic accumulation. Whereas tephra is unconsolidated,
a pyroclastic rock is produced from the consolidation of pyroclastic
accumulations into a coherent rock type.
Lava flows are much more thick and sticky so do not flow downhill as
easily.
These eruptions build up more steeply-sloping.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
1. Magma is an basaltic-intermediate type.
2. The «cap» isn’t thick so strombolianactivity is characterized by short-lived, explosive outbursts of pasty lava ejected a few tens or hundreds of meters into the air
3. The eruptions are quite frequent, evensteady, and not excessivelydangeruos.
Vulcanian eruption
1. Magma is felsic-intermediate type.
2. The cap is more thick ; the high viscosity of these magmas makes it difficult for the vesiculating gases to escape. This leads to the build up of high gas pressure and explosive eruptions.
3. Lava flows are quite absent, whiletephra and pyroclasts are present.
Strombolian eruption
1. Magma is felsic type.
2. Plinian eruptions generate large eruptive columns that are powered upward by the thrust of expanding gases, with exit velocities of several hundred meters per second. Some reach heights of ~45 km.
3. Lahar and pyroclastic flows
Plinian or vesuvian
eruption
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
These lethal mixtures of water
and tephra have the
consistency of wet concrete,
yet they can flow down the
slopes of volcanoes or down
river valleys at rapid speeds,
similar to fast-moving streams
of water. Lahars can vary from
hot to cold, they are
generated by the basal
melting of glacial ice or of
large quantities of snow and
ice, eventually by pouring rain.
They are the most deadly of all volcanic phenomena.
It is a mixture of solid to semi-solid fragments and hot, expanding gases that flows down the flank of a volcanic edifice. It moves like a snow avalanche, except that they are fiercely hot, contain toxic gases, and moving at hurricane-force speeds, often over 100 km/hour.
Pyroclastic flows
Lahars or volcanic mudflow
https://www.youtube.com/w
atch?v=kznwnpNTB6k
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Students at work 3!
Prepare at least three questions for your classmates. Be ready to answer them.
Write a short test (200 words) about one of the following eruption:Vesuvio, 79 d.c.Nevado del Ruiz, 1985Mont st. Helens, 1980Pinatubo, 1991Krakatoa, 1883Pelée, 1902
You have fifteen minutes! A wee joke!
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Hydrovolcanic eruption
are generated by the interaction of magma with either groundwater or surface water.
The high explosivity is a hallmark of hydrovolcanic activity: as the water is heated, it flashes to steam and expands explosively, thus fragmenting the magma into exceptionally fine-grained ash.
Note the radial cloud emanating from the base of the eruptive column. This phenomenon is a base surge, a characteristic of these eruptions, derived from the gravitational collapse of the "wet" eruptive column, which is denser than those associated with "dry" eruptions. Base surge deposits are wedge-shaped, with their thickest end near the vent.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Distribution of volcanoes
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Distribution of volcanoes
Volcanoes are not randomly distributed on the surface of the earth, rather
they are found in certain well-defined belts.
Ring of fire
or Circum -
Pacific belt
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
1. The Circum-Pacific belt:This is the most important belt of volcanoes. Itextends through the Andes of South America,Central America, Mexico, to the Mountains ofWestern United States, up to the AleutianIslands, then to Japan, the Philippines, NewGuinea, the Solomon Islands, New Caledonia
and New Zealand.This belt has 80 active volcanoes and meetsthe mid-continental belt in the East Indies. InAlaska there is a Valley of Ten ThousandSmokes.
2. The Mid-Continental Belt:This belt has various volcanoes ofthe Alpine mountain chain(exinct), Mediterranean Sea,
Volcanoes of the Aegean Sea. Mt.Ararat, Elburz and Hindukush arealso included in this belt.It is interesting that there areseveral volcanic free zones foundalong the Alps and the Himalayas.The Rift Valleys of Africa havevolcanoes such as Kilimanjaro,Elgon.
3. The Mid- Atlantic belt:As the name indicates, this belt includes thevolcanoes of the Mid-Atlantic Ridge. Thevolcanoes associated with the Atlantic Oceanare located either on swells or ridges rising fromthe sea floor, or on or near the edge of thecontinent where it slopes abruptly into thedeep oceanic basins. Volcanoes in this belt aregenerally of fissure-eruption type.
4. Hot spots: these are volcanoes that are not found on plate boundaries. they normally create a chain of volcanoes e.g. the islands of Hawaii.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017
Italian volcanoes
Extinct volcanoes. Volcanoes which last
erupted over 10,000 years ago are
defined as extinct. These include the
Amiata, Vulsini, Cimini, Vico, Sabatini,
Pontine Islands, Roccamonfina and
Vulture volcanoes
Dormant volcanoes.Whereas dormant volcanoes have
erupted during the last 10,000 years but are currently in a
period of dormancy. According to a more precise
definition, volcanoes having a current period of
dormancy shorter than the longest period of dormancy
registered previously are considered dormant. Here we
have: Colli Albani, Phlegraen Fields, Ischia, Vesuvius,
Salina, Lipari, Vulcano, Ferdinandea Island and
Pantelleria. Amongst these, Vesuvius, Vulcano and
Phlegraen Fields, have a very low eruptive frequency
and their conduits are now obstructed. Not all the
dormant volcanoes present the same risk level, both for
the hazard of expected phenomena as well as for the
differing extent of population under exposure.
Furthermore some have a secondary vulcanism
phenomena (degassing from the ground, fumaroles,
etc.) which may well cause situations of risk.
5D - Prof.ssa Silvana Berti - A.S. 2016/2017