What are the three types of volcanoes and what type of

eruptions does each volcano have?

What do you know about volcanoes?

And…Do you know of

any famous volcanoes?

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.

Where do volcanoes erupt?There are three places…

• Convergent plate boundaries – where two of Earth’s plates join together

• Divergent plate boundaries – where two of Earth’s plates move apart RING OF FIRE!!

• Hot spots – active areas below the earths crust

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

• 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

Stages of a Volcano• Magma chamber- the chamber below the volcano

that stores the magma.

• Without a magma chamber attached to the volcano it will be come extinct. With it, it is still considered active.

• If the volcano is still attached to its magma chamber but hasn’t erupted recently (100 years) it is considered to be dormant. It can still erupt at anytime!!

Types of VolcanoesThere are three major types of

volcanoes:

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

volcanoeLava 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 and

magnesium and is very fluid (low viscosity).

Shield Volcanoes• They have mild Eruptions that can

occur several times.• Mauna Loa and Kilaeua in Hawaii are

examples of a shield volcanoes.

Mauna Loa (Shield Volcano)

Kilauea Caldera

Kilauea Crater

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 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 Thermal Imaging

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).

• The magma inside a cinder cone volcano has large amounts of silica (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.

Cinder Cone Volcanoes

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

• 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.

Mount Vesuvius

What do you notice in this picture?

Mount Vesuvius Thermal Imaging

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!

Pyroclastic Flows can even travel across

water!

Ash and Pumice distribution

People of Pompeii

Animals of Pompeii

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

Lava• Lava is molten rock expelled by a

volcano during an eruption. • Lava is a liquid at temperatures

ranging from 1,300 °F to 2,200 °F. • Although lava is about 100,000 times

the viscosity of water, it can flow great distances before cooling and solidifying.

• Dangerous because…• Lava can kill people, animals, and

destroy property and even bury entire towns!

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

Kona Lava Fields

Lava Tubes

Thurston’s Lava Tube