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Earthquakes IntroductionIzmit earthquakeFloods Thessaloniki (Greece)Hurricanes Storm surgesHurricane KatrinaVolcanoes Introduction Andean Volcanic BeltEtnaNyiragongo and Nyamuragira
| | | | | | | Introduction
Volcanoes and how they work
A volcano usually resembles a mountain in the shape of a cone. It is an opening of the surface of the Earth downward to a pool of extremely hot, molten rock (magma).
Volcanoes are locations where new Earth is born. They represent a superlative of geological processes. On the one hand, processes can be very slow, and on the other, very fast and dramatic, in the form of eruptions and earthquakes.
When pressure builds up, eruptions occur. Eruption products consist of lava (magma that reaches the surface of the Earth) and gases that come up and spill over the sides of the volcano or fill the air with volcanic material. As a result of a volcanic eruption, one can find lava flows, mudflows, falling ash and much more.
How many volcanoes are active and dangerous?
- 1500 volcanoes are potentially active on Earth
- 70 volcanoes are currently in eruption
- 10% of the human population is directly exposed to volcanic risk
Several large cities are located close to an active or dormant volcano.
Volcanic damage from 1900 to 2006
| | Number of events | People killed | Homeless | Total Affected | Damage (Million$) | | Africa | 15 | 2213 | 180 710 | 500 353 | 9 | | Americas | 69 | 67 841 | 35 680 | 1 123 587 | 2808 | | Asia | 80 | 21 456 | 97 900 | 2 668 287 | 697 | | Europe | 11 | 783 | 14 000 | 26 224 | 44 | | Oceania | 20 | 3665 | 46 000 | 248 422 | 400 |
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Are all volcanoes the same? What are their characteristics?
There are several types of volcanoes. They basically differ in shape, composition, and type of eruption. Volcanic scenery may look like any of the following:
Different classifications of volcanoes can be found in the various sources below:
http://pubs.usgs.gov/gip/volc/types.html
http://www.geology.sdsu.edu/how_volcanoes_work/Volcano_types
http://library.thinkquest.org/17457/volcanoes/types.php
http://en.wikipedia.org/wiki/Volcano
The volcano types we will be studying in the exercises are:
Strato volcano (Composite volcano): explosive eruptions, pyrocalstics, symmetrical, steep slopes;
Shield volcano: non-explosive eruptions, fluid basaltic lava, gentle broad slopes
The eruptive behaviour of a volcano depends on the magma’s viscosity (a quantity that is related to a fluid's resistance to flow). High viscosity (high resistance to flow) causes an explosive activity, and low viscosity an effusive activity.
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| | Volcanoes More on volcanoes Volcanoes on EarthVolcanic hazardsVolcano monitoring
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