Post on 13-Jan-2016
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