Volcanoes

“And the mountains shall be molten under Him, and the valleys shall be cleft, as wax before the fire, and as the waters that are poured down a steep place.”

Micah 1:4

Volcanoes

• Volcanoes are the most violent of commonly occurring natural cataclysms.

• They give us a glimpse of the interior of the earth.

Volcanic Structure

A volcano is an opening in the earth’s surface though which hot gases, ash, and molten rock are ejected from the earth’s interior.

Volcano Characteristics

1.Vent – the central channel which ejects ash, gases, and rock.

2.Magma – a reservoir of molten rock that may be three or four miles beneath the surface.

3.Cone – the ejected materials accumulate to produce a conical shaped mountain.

4.Crater – the cone is capped by a bowl shaped depression surrounding the vent.

Volcanology

Volcanology is the study of volcanoes.

Vulcanologists are scientists who study volcanoes.

Today vulcanologists in certain areas give warning to eruptions and they are better able to warn residents.

Types of Volcanoes

There are three common types of volcanoes:

1. Cinder-cone volcanoes 2. Shield volcanoes3. Composite volcanoes

Cinder-cone Volcanoes

• These are volcanoes that consist primarily of erupted volcanic ash and rock fragments.

• They are composed of loose materials• They do not grow large and are usually

formed by a single eruption.

Shield Volcanoes

• These volcanoes pour out lava in large quantities during gentle eruptions.

• They produce a broad, gentle sloping volcano.

Example: Mauna Kea in Hawaii

Composite Volcanoes

• These volcanoes produce both cinders and lava.

• They have a steeper dome.• These are highly explosive volcanoes.

Example: Mt. Rainer and Mt. Saint Helens

Active and Dormant VolcanoesGeologists classify volcanoes in three ways:

1. Active – a volcano that has erupted within the past 50 years.

2. Dormant – now inactive – appears “at rest” – Mammoth is an example and Lassen Peak

3. Extinct – will probably not erupt again – Mount Shasta is an example

Volcanoes are unpredictable and it is difficult to tell if a volcano is dormant or truly extinct.

http://dsc.discovery.com/convergence/supervolcano/interactive/interactive.html

Location of Volcanoes

• Almost all of the earth’s volcanoes occur in three main belts that correspond to the earth’s earthquake belts.

• The most important belt encircles the Pacific Ocean Basin

called the “Ring of Fire”

Volcanic Eruptions

• Volcanoes rarely erupt without warning.• They usually have some swelling or bulging -

the bulging is caused by the magma chamber filling with magma and gases.

• Mt. Saint Helens had a bulge and it enabled scientist to warn residents and save lives.

• Earthquakes may also precede an eruption.

Volcanic Eruptions

• The first explosion may produce a great cloud of volcanic gases, steam, and dust that moves into the atmosphere several miles.

• This cloud is often accompanied by heavier rock and lave hurled into the air.

• The eruption may last for weeks, months, or even years.

Volcanic Eruptions

Not all volcanoes erupt explosively…Volcanologists have discovered the violence of an eruption depends on two things:

1. Viscosity – the thickness of the magma – the thicker the more violent the eruption

2. The amount of dissolved gas in the magma – If the gases cannot escape easily (the magma is too thick) they build up to a greater explosion.

Volcanoes and Plate Tectonics

There are several types of plate boundaries…the places where the plates are up against each other.

1. Divergent2. Convergent3. Transform

Divergent Plate Boundary

Divergent Plate Boundary

• Plates are coming apart…• Example: Mid-Atlantic Ridge• Example: Kenya – East African Rift

Convergent Plate Boundary

Convergent Plate Boundary

• Plates crashing into plates…• Example: Andes Mountains

Transform Plate Boundary

Transform Plate Boundary

• Plates slide past plates…• San Andreas

Volcanic Ejecta

There are three types of ejections:

1. Gaseous ejecta2. Liquid ejecta3. Solid ejeta

Gaseous Ejecta

• 70 percent of gases consist of water vapor• Other gases include carbon dioxide,

nitrogen, sulfur dioxide, hydrogen, fluorine, and hydrochloric acid

• Many of these gases is poisonous and can cause sickness and death miles around.

• Sulfur dioxide makes acid rain.

Liquid Ejecta

• Includes Lava

Solid Ejecta

• Formed when molten lava is ejected into the air.

• Particles or blocks of solid volcanic ejecta are called pyroclasts.

• When pyroclasts are small, they are carried by the wind in the form of ash.

• Volcanic bombs are formed when lava is thrown high into the air in a liquid state and hardens before it hits the ground.

Fiery Blasts

• The most dangerous part of an eruption is the fierce blast of incandescent ash and superheated gases that accompanies some volcanic eruptions.

Volcanic Structures

• Calderas – the bowl shaped crater in the ground at least two miles across.

• Tunnels – lava tunnels remain after the lava cools – the largest known is in Hawaii – it winds 6 miles beneath the surface.