a volcano is a mountain that forms when molten rock is forced to the earth’s surface. volcanoes...

A volcano is a mountain that forms when molten rock is forced to the Earth’s surface.

Volcanoes can by active, dormant, or extinct.

Active Volcano…

Kilauea Volcano is presently one of the most active volcanoes on Earth.

Dormant “Sleeping” Volcano

Dormant Volcano: A volcano which is presently inactive but which may erupt again. Most of the major Cascade volcanoes are believed

to be dormant rather than extinct.

Mt. Hood, Oregon

Extinct Volcano

Extinct Volcano: A volcano that is not presently erupting and is not likely to do so for a very long time in the future.

Kohala Volcano

Where do volcanoes form?

1. Volcanoes form when hot material from below rises and leaks into the crust.

2. Eventually, but not always, the magma erupts onto the surface. Strong earthquakes accompany rising magma.

Parícutin, Mexico, 1943

• In the winter of 1943, the countryside near Parícutin, Mexico was rocked by a series of earthquakes. The tremors lasted for nearly two weeks when a fissure open in a farmer's field and the birth of cinder cone was underway. Within 12 hours of the initial eruption, the fissure was ejecting pyroclastic material as well as huge clouds of gas and ash. Lava began to spill from the base of the cone building the volcano laterally.

Parícutin, Mexico, 1943

• Within 24 hours a 40 meter high cone hurling volcanic bombs several kilometers away had been built.

• After nine years of activity, two villages had been buried

Anatomy of a Volcano…

Vent - The opening through which the molten rock flows onto the surface.

Crater- A bowl-shaped depression at the mouth of a volcano

Magma chamber -A large underground pool of molten rock lying under the surface of the earth's crust

What is the difference between magma and lava??

Magma – molten rock deep inside the earth.

Lava – molten rock on the earth’s surface.

II. What erupts from a volcano?

• Gases:

Water Vapor, Carbon Dioxide, Sulfur Dioxide, Nitrogen, Hydrogen, Argon

• Rock Fragments:

Dust, ash, bombs, and blocks

• LAVA!!

IV. Types of Lava and Rock

Fragments

Pahoehoe - Smooth, wrinkled lava

aa – Sharp, jagged lava

Pillow Lava…

Pillow lava – forms on the ocean floor and cools into rounded blobs.

Pyroclastic material - avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano

In Greek:

Pyro – “fire” Clastic – “Broken”

Mt. St. Helens

Mt. Pinatubo

Volcanic ash – 2 mm in diameter

Volcanic dust - < 0.25 mm in diameter

Lapilli – less than 64 mm in diameter

Rock Fragments

Volcanic blocks – greater than 64 cm in diameter

Volcanic bombs – greater then 64 mm in diameter

III. Types of Volcanoes

Shield Volcanoes

a. Nonexplosive

b. Thin, runny lava

c. Gently sloping

d. Dome-shaped mountains

Stratovolcano or Composite

a. Alternating layers of rock particles and thick lava.

b. Violent eruptions

c. Large cone-shaped mountain

d. Most common type.

Cinder Cone

a. Different sizes of volcanic material

b. Explosive eruptions

c. Large bowl-shaped craters

d. Steep sides with loose rock particles

Mafic Lava Felsic Lava

What type of volcano am I?

Stromboli Volcano in Italy

Mt. St. Helens, WA

Kanaga Volcano in Alaska

Sunset Crater, Arizona

Mauna Loa Volcano, Hawaii

• Water (steam) 77.0%• Carbon dioxide 11.7%• Nitrogen 3.0%• Carbon monoxide 0.5%• Hydrogen 0.5%• Sulfur dioxide 6.5%• Sulfur 0.3%• Chlorine 0.05%• Argon 0.05%