VolcanoesPart 1

Volcano History

The word volcano comes from

Vulcan, the Roman god of fire and

metalworking who “lived” under Mt.

Etna.

The Study of Volcanoes is

referred to as volcanology.

Volcano: A landform that

develops where lava, ash, and

gas erupt.

How do volcanoes Form?

There are two major ways volcanoes

form:

Convergence of Tectonic Plates

Hot Spots

ConvergenceWhen two tectonic plates collide:

1. There is subduction of a plate into the

asthenosphere.

2. The plate begins to melt rock, forming magma.

3. The hot, low density magma rises toward Earth’s

surface.

Convergence

When two tectonic plates collide:

4. Pressure pushing up on Earth’s crust gets higher and higher.

5. Eventually, magma pushing up forms a crack called a fissure.

6. Magma erupts through the fissure and onto Earth’s surface.

7. Magma that is above Earth’s surface is called lava.

After several eruptions, lava builds up and a rocky hill, a volcano is formed.

Hot Spot A hot spot can also form a volcano:

1. A hot spot is an area in the lower mantle that is really hot.

2. Since it is so hot, parts of the mantle melt and form magma.

3. Hot magma rises because it is less dense.

4. Pressure is put onto the surface of the Earth, forming a fissure.

5. A volcano is formed over many eruptions.

Examples: Hawaii, Yellowstone

Hot spots are normally found inside of plates, not at boundaries.

Hot Spot Example: Hawaii

1. Hawaii sits on the Pacific Plate, which is moving Northwest.

2. There is a hot spot under Hawaii causing magma to rise.

3. The hot spot is located in the mantle, and is not moving.

4. The plate moves over the hot spot, forming a line of volcanoes.

Which islands are the oldest, the northern or the southern islands?

The type of volcano and how it erupts

depends on magma’s viscosity:

Thick / Viscous Magma

Honey or Molasses

Does not flow very easily.

Why is Magma Viscous?

Low temperatures

High Silica content

• Thin/ Non-Viscous

Magma

– Water

– Flows very easily.

• Why is Magma Non-

Viscous?

– High temperatures

– Low Silica content

VISCOSITY: How easily a liquid will flow

Why Silica?The more Silica in magma, the thicker and more

viscous it is.

Silica tetrahedrons link together in long chains that

stop magma from flowing easily.

Lava Flow

What about the Magma? Magma with Silica content that is…

HIGH

Granitic Magma

Medium

Andesitic Magma

Low

Basaltic Magma

VISCOUS MAGMA

• Low Temperature

• High Silica

• Called Granitic Magma

Medium Viscous Magma

• Medium Temperature

• Medium Silica

• Called Andesitic Magma

Non-Viscous Magma

• High Temperature

• Low Silica

• Called Basaltic Magma

Why is Viscosity so important

anyway?

Thick and Viscous Magma

1. There are gasses in magma, such as Water Vapor and

CO2.

2. Gasses rise up toward Earth’s surface with the magma.

3. If the magma is thick, it does not flow up easily and

GETS STUCK!

4. Rising gasses also get stuck and can not escape.

5. The gasses build up pressure until they explosively erupt.

Why is Viscosity so important

anyway?

Thin and Non-Viscous Magma

1. If the magma is thin, it flows up easily and

DOES NOT GET STUCK.

2. Rising gasses also flow up and can easily

escape.

3. Pressure does not build up and magma

gently erupts.

GENTLE

ERUPTION

MODERATELY

EXPLOSIVE ERUPTION

EXPLOSIVE

ERUPTION

Volcanoes The type of volcano and how it erupts depends on…MAGMA’s

VISCOSITY.

VISCOUS MAGMA

• Low Temperature

• High Silica

• Called Granitic Magma

Medium Viscous Magma

• Medium Temperature

• Medium Silica

• Called Andesitic Magma

Non-Viscous Magma

• High Temperature

• Low Silica

• Called Basaltic Magma

Volcanoes

You must know the following:

Type of Volcano

Temperature

Silica Content

Eruption Style