VOLCANOES - copernico.edu.itcopernico.edu.it/wordpress/wp-content/uploads/2017/CLIL/clil2.pdf · eventually build up into large, broad shield volcanoes. Eruptions are common in central

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.


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


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/

3

6

5

8

9

7

4

2

1


http://geology.com/volcanoes/

http://geology.com/dictionary/glossary-v.shtml

http://www.universetoday.com/29125/parts-of-a-volcano/

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.


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


There are many types of volcanic structures

And they are a consequence of the magma and lava composition.


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


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


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.


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.


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


ERUPTION STYLES

Eruption styles from nonexplosive to explosive

Fissure eruptions or Icelandic eruptions

Hawaiian eruptions

Strombolian eruptions

Vulcanian eruptions

Plinian eruptions

Hydrovulcanic eruptions


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.


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.


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.


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


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


https://www.youtube.com/watch?v=kznwnpNTB6k

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!


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.


Distribution of volcanoes


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


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.


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.


Documents

VOLCANOES - copernico.edu.itcopernico.edu.it/wordpress/wp-content/uploads/2017/CLIL/clil2.pdf · eventually build up into large, broad shield volcanoes. Eruptions are common in central