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Social sciences: geography

Grade 7

Natural hazards

Module 5

Volcanoes

1. The occurrence and causes of volcanoes

Molten rock below the earth’s crust is called magma. When it flows to the surface it is called lava. Why lava flows to the surface is not clear enough for people to agree on the reasons for eruptions and no one has been able to investigate the heart of the earth to find out what happens there.

We do know, however, that the weight of the solid crust of the earth is so great that the fluid rock is forced upwards at weak places in the earth’s crust. This molten rock is extremely hot, with temperatures of between 800 and 1 500 C.

If you shake a can of cooldrink, the gas will propel the cooldrink out of the can with great force when you open the can. This is what happens in the case of volcanoes – the molten rock erupts through weak places in the earth’s crust and lava, rocks and ash are propelled into the air.

Then the lava cools down and solidifies to form new rocks known as igneous rock.

Some volcanoes produce very fluid lava that flows over a large area before solidifying. Thin plates of igneous rock are formed in this case. Other volcanoes build up domes because the lava is less fluid and does not flow far from the core.

A very forceful explosion can force out the whole of the dome and cause a large open hole called a caldera, or crater. There are roughly 450 active volcanoes worldwide. Fortunately, they do not erupt continuously and are therefore referred to as dormant volcanoes.

Where do most volcanoes occur?

Study figure 4.

There are about 5 000 volcanoes. They only occur in particular places. These places are situated above the margins of the large plates of the earth’s crust. The movement of these plates lead to volcanic eruptions and earthquakes.

Quake areasVolcanic areas

Figure 4

The distribution of the main volcanic and earthquake areas of the earth

Which volcanoes have caused the greatest destruction?

The most destructive volcano of all time was Krakatoa, in Indonesia. When it erupted in 1883, more than 36 000 people died. The bang of the explosion was heard 5 000 km away and the pollution that resulted from the eruption was visible in copper-coloured sunsets across the earth for years.

Another well-known example of the destructive force of a volcano comes from the eruption of Mount Vesuvius, which buried the city of Pompeii in the Bay of Naples under volcanic rocks and ashes in 79 AD.

2. The effect (consequences) of volcanoes on people’s lives and their socio-economic activities

Thousands of lights glitter in the dark dome of the night. From a distance the explosions that hurtle glowing rocks and streams of fire into the night look like an expansive display of fireworks. Rocks and ashes flung up high pollute the air.

A river of red, smoking lava slithers over the edge of the crater – the warm blood of the living earth, as someone has strikingly described it.

It may flow through fertile valleys for kilometres, devouring every blade of grass, even trees, along its way. Houses crumble and cities are buried under the glowing, driven mass. People who have survived, scramble down the mountainside; warm ash raining down on them. Suffocating sulphurous gases and a rain of ashes smother other people to death.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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Source:  OpenStax, Geography grade 7. OpenStax CNX. Sep 09, 2009 Download for free at http://cnx.org/content/col11021/1.1
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