Volcanoes

The cause of it all…• What do you think causes volcanoes to

erupt?

• The shift in the Earth’s plates are what causes volcanoes to form and erupt.

• As the plates join or separate some of the molten rock is exposed.

Volcanoes of the World

Structure of a Volcano

• Magma – the molten, or liquid-like, rock within the Earth

• Lava – magma that reaches Earth’s surface and is exposed to O2 (two types of lava are Pahoehoe and Aa)

• Viscosity~ Low viscosity = water high viscosity = maple syrup

• Vent – an opening through which molten (liquid-like) rock flows onto Earth’s surface. Volcanoes will have many side vents through which lava will flow out of!

• Crater- the central opening at the top or summit of volcano.

• Volcanoes always have one central vent, but can also have several smaller side vents.

•(thickness), resistance of a liquid to flow.

Structure of a Volcano

magma

central vent

side vent

lava

old layers of lava

ash cloud

Earth’s crust

Types of VolcanoesThere are three major types of

volcanoes:

Shield volcanoesComposite volcanoesCinder cone volcanoes But there is also a fourth major volcanoLava domes

Shield Volcanoes• The flowing lava gives the volcano

gently sloping sides.• They have mild Eruptions that can

occur several times. • The lava tends to flow great

distances. • The magma rich in iron (Fe) and

magnesium (Mg) and is very fluid (low viscosity).

Shield Volcanoes• Mauna Loa and Kilauea in Hawaii are

examples of a shield volcanoes.

Composite Volcanoes

• They have much steeper slopes than shield volcanoes.

• They have alternating layers of lava and cinders.

• Eruptions can be flowing lava or explosions. Explosive eruptions come from the trapped gases and produce cinders and ash.

Composite Volcanoes

• The magma is rich in silica (Si) and much thicker than magma from a shield volcano.

• Gases get trapped inside this thicker magma.

• Mount Fuji in Japan and Mount St. Helens in Washington State in the US are examples of composite volcanoes.

Mt. Fuji (Composite Volcano)

• Stands over 13,000 ft. tall

• Surrounded by 5 lakes• Last erupted in 1707-

08.

Mount St. Helen’s Composite Volcano

Mount St. Helen’s before and after eruption

1979 1980

Cinder Cone Volcanoes

• Cinder Cones have very steep sides!• Usually only active for a short time and then

become dormant (inactive).• ***Most Dangerous type of Volcano!***

• Violent and explosive eruptions because of all the gas trapped in the magma.

Cinder Cone Volcanoes• The magma inside a cinder cone

volcano has large amounts of silica (Si) (63%) and gas trapped in it.

• The large amounts of hot ash and lava thrown out of the vent fall to the ground forming the cone shape that these volcanoes have.

• Paricutin in Mexico and Mount Vesuvius in Italy are examples of a cinder cone volcanoes.

Paricutin Volcano (Cinder Cone)

• Grew over 5 stories in the first week• Continued to erupt for 8 years

reaching a height of over 1,300 ft.

Volcanic Dangers• Pyroclastic flows• Lahars• Lava• Volcanic ash• Volcanic gas

Which volcanic danger kills most people?Volcanic

Ash

Pyroclastic flows• Pyroclastic flows

mixtures of hot gases, ash and rocks that travel about 450mi/hr down the sides of volcanoes. 

• Dangerous because… • The poisonous gases can

be as hot as 1,000 degrees.

• They destroy anything in its path!

• They are rare and don’t happen in every eruption!

Lahars• Lahars are

mudflows formed by the mixing of volcanic particles and water.

• Dangerous because…

• Carry large boulders and logs down the side of a volcanoes.

• Can easily crush or shear off anything in its path!

Damage caused from Lahars

Types of Lava• Pahoehoe lava is

runny and fast moving (up to 50 km/h).

• Has high iron content.

Pahoehoe Lava

Types of Lava

• Aa flows are chunky and slow moving lava flows

• Has a high silica content

Aa Lava

Lava CompositionWhich element is found most in lava? • Lava is about 50%

Silicon. • Silicon makes lava thick

(high viscosity).• The more silicon you

have in lava the more explosive the eruptions will be in a volcano.

• What is building up?• Gas and pressure build

up under the thick magma.

Silicon!

Then Dangers of Lava!

Lava at Night!

Technology in Science• Using infrared, scientists

were able to identify specific warning signs before the eruption of the nearby Bezymianny volcano (Russia) in December 2006.

• Flowing lava shows up as bright yellow in an infrared image (top) of Russia's Klyuchevskoy volcano.

Volcanic ash• Volcanic ash- small

sharp glass-particles that damage anything they come across.

• Volcanic ash exploded from a vent in fragments less than 2mm in size. 

• Dangerous because… • Can cause houses and

buildings to collapse.• People and animals may

die from lack of oxygen.• *kills most people

Volcanic gas• Volcanic gas is gases

contained within magma.

• * Water Vapor is the gas that is released the most

• Other gases include carbon dioxide (CO2), *sulfur dioxide (SO2), and hydrogen sulfide (H2S).

• Dangerous because…• These gases can kill

people and animals and cause acid rain and contribute to greenhouse effects.

Volcanoes are the largest natural polluters!

Global Impact• When a volcano erupts

it throws out a lot of ash.  At short notice this ash can be very harmful to the environment by killing plants and animals.

• However, over a long period of time, the ash layer contains many useful minerals, that are converted into fertile soil.

• Volcanoes provide resources for energy extraction, also called geothermal energy. 

• Heat from the earth's crust is being converted to energy.  Advantages to geothermal energy are that it is very clean and the resources are nearly inexhaustible.

Positives and Negatives of Volcanoes

Positives• Lava flows create

extremely fertile soil for crops and plants.

• Creates new beautiful land (over long periods of time)

• Emits water vapor into atmosphere

• Create Geothermal energy

• Help us understand past civilizations (Pompeii) and cultures and even the Earth itself!

Negatives• Getting caught in volcanic

dangers (blasts, lava flows, pyroclastic flows, lahars, and

ash clouds) is deadly.• Destroys anything in their

path.• Puts out large amounts of carbon dioxide (greenhouse

gas) and sulfur dioxide. • SO2 is a cooling gas that can

drop global temperatures after a large eruption.

• SO2 also causes acid rain