Characteristics and Spatial Distribution of Volcanes of Group D - John, Na Li and Bettina

Volcanoes are mountains or hills, that have a crater or vent through which lava, rock fragments, hot vapour, and gas are being or have been erupted from the earth's crust.

The Characteristics of a Volcano:
Duration: The duration of a volcanic eruption can last from less than a day to thousands of years. Shown in the table below, the biggest percentage of volcanic eruption duration is one to six months, with about 28% of the earth's eruptions, and 99% of the eruptions are within 20 years.

Length of Eruption	% of Eruptions	Cumulative Total %
< 1 day	10	10
1 day to 1 week	14	24
1 week to 1 month	20	44
1 to 6 months	28	72
6 months to 1 year	12	84
1 to 2 years	7	91
2 to 5 years	5	96
5 to 10 years	2	98
10 to 20 years	1	99
> 20 years	1	100

http://www.volcanolive.com/predictions.html

Magnitude: It is said that there is no single feature in measuring how big a volcano is, however, there is a scale that determines the magnitude of the eruption. The scale to measure the magnitude of the eruption is called the Volcanic Explosivity Index, or the VEI. 

VEI	Description	Plume Height	Volume	Classification	How often	Example
0	non-explosive	< 100 m	1000s m3	Hawaiian	daily	Kilauea
1	gentle	100-1000 m	10,000s m3	Haw/Strombolian	daily	Stromboli
2	explosive	1-5 km	1,000,000s m3	Strom/Vulcanian	weekly	Galeras, 1992
3	severe	3-15 km	10,000,000s m3	Vulcanian	yearly	Ruiz, 1985
4	cataclysmic	10-25 km	100,000,000s m3	Vulc/Plinian	10's of years	Galunggung, 1982
5	paroxysmal	>25 km	1 km3	Plinian	100's of years	St. Helens, 1980
6	colossal	>25 km	10s km3	Plin/Ultra-Plinian	100's of years	Krakatau, 1883
7	super-colossal	>25 km	100s km3	Ultra-Plinian	1000's of years	Tambora, 1815
8	mega-colossal	>25 km	1,000s km3	Ultra-Plinian	10,000's of years	Yellowstone, 2 Ma

http://volcano.oregonstate.edu/education/eruption_scale.html

Predictability: Volcanic eruptions are very difficult to predict, however, it is said that the beginning of a volcanic eruption is easier to predict than to predict the end of a volcanic eruption.
Volcanologists can try and predict the eruptions of volcanoes by looking for certain characteristics:

• Changes in the shape of a volcano 
• Changes in the amount of gas being released
• Changes in the temperature
• Tectonic Activity (earthquakes)
• Animal behaviour
• Changes in local hydrology
• Mass movements

Regularity and Frequency: Shown in the Volcanic Explosivity Index table, non-explosive to gentle explosions occur frequently, and daily, compared to very big volcanic eruptions with a plume height of >25 km, which happen about once every 10,000 years. 

Volcanic Features: There are many different features or types of volcanoes:
Volcanic Fissure Vents: which is a linear crack where lava emerges
Shield Volcanoes: have a broad, shield-like profile, and are formed by the eruption of low-viscosity lava. Shield Volcanoes are usually found in the oceanic setting rather than the continental setting
Lava Domes: are built through slow eruptions with highly viscous lava. Lava domes can potentially produce violent, and explosive eruptions, however, the lava generally does not flow far from the vent
Cryptodomes: these are formed when viscous lava forces its way up and produces a bulge such as the 1980 eruption of Mt. St. Helens
Volcanic Cones: these are results of eruptions of small pieces of scoria and pyroclastics that build around the vents
Stratovolcanoes: are composite volcanoes that are composed of lava flows
Supervolcanoes: a large volcano that can potentially produce devastation on an enormous scale
Submarine volcanoes: these are volcanoes that can be found in the ocean, and are sometimes active in shallow water
Subglacial volcanoes: these are volcanoes that are developed under icecaps
Mud volcanoes: these are formed through geo-excreted liquids and gases

Spatial Distribution of a Volcano:
Volcanoes can be found in continental settings or oceanic settings. This means that volcanoes can be found in either land or underwater.  
Volcanoes can be located in specific areas:

• Around the edge of the Pacific Ocean
• Down the centre of the Atlantic Ocean
• In Southern Europe
• Down the East Coast of Africa

Volcanoes are located on or near tectonic plate boundaries, specifically destructive and constructive boundaries. Their spatial concentration is limited, and their areal extent is also normally limited to the areas immediately around the volcanoes.

Examples
Mt. Pinatubo:

• Second largest eruption in the 20th century
• Located in the Philippines
• Ashes were about 5cm thick covering 4,000 square kilometers
• Affected weather around the globe - aerosol droplets reflecting sunlight causing cooling of the Earth (1.5 celsius) and reducing density of the ozone layer
• Has caused a total of 722 deaths and 200,000 individuals homeless

Mountain St. Helens:

• A volcano located in Washington in the United States
• Created a major eruption in the United States and is considered to be the most destructive in U.S. history
• Its type of volcano is a cryptodome, as the lava forced its way up
• On May 18, ash erupted from the volcano for about nine hours
• About fifty-seven people were known to be dead
• Two-hundred homes were destroyed
• 185 miles of road and 15 miles of railways were destroyed

Villarica Volcano in Chile:

• One of Chile's most active volcanoes
• Lava of basaltic-andesitic composition --> of only five volcanoes worldwide known to have an active lava lake within its crater
• Generates strombolian eruptions with ejection of incandescent pyroclasts and lava flows
• The upper part of the volcano is permanently covered by snow and has some 40km^2 of glaciers
• It is a stratovolcano
• Last eruption was in 2013
• Villaricca emerged as a volcano during the Middle Pleistocone and grew forming a large stratocone of similar dimensions to the current edifice. 100,000 years ago during the Valdivia Interglacial the ancestral Villarrica collapsed following an eruption and formed a large elliptical calder of 6.5 and 4.2 km in diameter
• Currently the volcano covers up an area of 400km squared and has volcume of 250km (cubed) according to estimates
• Spatial Distribution:
• Located in Chile
• Symmetrical edifice stands in the Chilean Central Valley as the westernmost of an alignment of three large stratovolcanoes
• Alignment is attributed to the existence of an old fracture in the crust, the North-West-West trending sinistral Gastre Fault Zone, the other volcanoes in the chain Quetrupillan and Lanin are far less active. This alignment is unusual as it crosses the N-S running Liquine-Ofqui Fault, around which most currently active volcanoes are aligned.