Volcano:

an opening in the earth’s surface through which lava, hot gases, and rock fragments erupt

Introduction to volcanoes

1. Magma 50-100 miles below the earth’s surface slowly begins to rise to the surface

2. As the magma rises it melts gaps in the surrounding rock

3. As more magma rises a large reservoir forms as close as 2 miles below the surface (magma chamber)

Origin of Volcanoes

4. Pressure from the surrounding rock causes the magma to blast or melt a conduit (channel) to the surface where magma erupts onto the surface through a vent (opening)

Origin of Volcanoes

5. The magma, now called lava, builds up at the vent forming a volcano

Origin of Volcanoes

6. Often the volcano sides will be higher than the vent forming a depression called a crater

Origin of Volcanoes

Crater:

Caldera: an unusually large crater or the remains when the cone collapses into its own magma chamber

Anatomy of a VolcanoCone:

the above ground structure built from lava and/or tephra

Conduit: the path that magma takes from the magma chamber to the vent

Magma Chamber: the reservoir located under the volcano where magma collects and becomes the supply of magma/lava to build the volcano

Parasitic Cone: a smaller secondary volcano

built on the side of or near the main volcano, but sharing the same conduit to the magma chamber

Fumarole: a secondary vent that emits only gases

Fissure: a long fissure (crack) from which lava flows

Vent: opening of the volcano, through which lava, ash and gases flow

Take a minute to label the parts on the diagram (not all parts are shown)

Magma chamber

conduitmantle

Parasitic Cone

Ash Cloud/Gases Vent

Lava Flow

Crater

Lava— There are 3 kinds:

Pahoehoe lava:

Hot, thin, fast flowing

harden with a relatively smooth surface

Often has a ropy or wrinkled appearance

Pahoehoe lava:

Aa lava: • Cooler,

thicker, slow moving

• Hardens with a rough, jagged, sharp edge surface

Pillow Lava: Lava suddenly cooled

by water shows sack-like

segments (stuffed pillows)

Can you identify the kinds of lava from the pictures? Circle

your choice.

Tephra (pyroclastic, rock fragments)

Volcanic Dust: Smallest particles and carried by atmosphere circulation

Volcanic Ash: 0.25-0.5 cm diameter Generally settles out within miles

of the cone but can be carried greater distances by stronger winds.

Forms a mudflow when mixed with water

Bomb: Smaller bombs (gravel, pea size) are

called cinders. Walnut size bombs are called lapilli. Larger fragments up to 4+ feet in

diameter are called bombs.

Lahar (mudflow): mixture of ash, eroded land,

and water flowing down river valleys

Lahar (mudflow):

Gases: water vapor, carbon dioxide, nitrogen, sulfur dioxide, hydrogen sulfide, chlorine

Divergent Boundaries: As the plate move long

cracks (rifts) form and lava builds up forming volcanoes.

Locations of Volcanoes

If the boundary is on the ocean floor, volcanoes can grow tall enough to break the surface of the ocean and become islands (Iceland)

Convergent Boundaries: Places where plates are

moving toward each other forming a subduction zone.

One plate melts under the other and the magma moves upward to form volcanoes.

Example: Pacific Ring of Fire

Example: Cascade Volcanoes

Magma that may originate in the mantle or outer core will move upward, breaking the surface and forming a volcano, they are independent of plate boundaries and a chain of volcanoes may form as the plate moves across a hot spot.

Hot Spots

(Examples: Hawaiian Islands and Yellowstone National Park)

Hot Spots

Two factors determine the type of eruption:

Amount of water vapor & other gases in the magma

The chemical composition of the magma

Types of Volcanic Eruptions

Trapped gases under high pressure will violently explode when the magma reaches the lower pressure of the surface.

Has granitic magma is very thick and plugs the vent causing the pressure to build until it blows violently out the vent

The high water content of the magma produces more water vapor which when mixed in granitic magma produces explosive eruptions

Explosive Eruptions

Explosive Eruptions

Mt. St. HelensMont serrat

Mt. Pinatubo

Low pressure gas Has basaltic magma (is

more fluid and will flow instead of explode)

And has low water content

Quiet Eruptions

Cinder Cones: Small base, steep-sided, loosely

consolidated Up to 1000 feet tall Life span of a few years Commonly built from gravel size

lava rock fragments call cinders Has violent eruptions, dangerous

when close.

Types of Volcano Mountains

Cinder Cones:

Types of Volcano Mountains

High pressure gas bubbles cause thick lava to explode into the air; lava begins to cool as it rises and falls, becoming very sticky

When lava hits the ground it sticks rather than flows

This builds a steep cone with a small base

Sketch a Cinder Cone Volcano:

Types of Volcano Mountains

Shield Volcanoes: Large base, gentle slope, lava

rock layers A few miles wide Life span of a million years or

more The lava is hot, thin, very fluid,

often basaltic. Example: Hawaiian Islands

Shield volcano on Mars; Taken from space

Take a look at these examples:http://www.volcano.si.edu/world/tpgallery.cfm?category=Shield%20Volcanoes

The Mauna Loa volcano in Hawaii—the largest volcano on Earth—has the broad expanse characteristic of shield volcanoes. It spreads across half the island of Hawaii.

Shield Volcanoes

Mauna Kea

Sketch a sheild Volcano:

Composite (strato) Volcanoes: Large mountain volcano often snow

capped, a few miles high Life span of million years or more Have alternating eruptions of tephra (air-

borne) and lava. The tephra adds height to the volcano and the lava cements the tephra together and adds to the base.

Found mostly in subduction zones and have violent eruptions.

Examples: Mt Rainier, Mt Fuji, Mt Kilimanjaro

Types of Volcano Mountains

Composite (strato) Volcanoes: (Make a Flip-Book)

Mt. Rainier

Mt. Fuji

Mt. Kilimanjaro

Sketch a composite Volcano:

Active (awake): Has erupted within recent time

and can erupt again at any time. Pre-eruption activities:

Increase in earthquake activity under the cone

increase in temperature of cone, melting of ice/snow in the

crater swelling of the cone steam eruptions minor ash eruptions

Volcano Activity Levels (Stages)

Mt St. Helens

Dormant (sleeping):

No eruption within recent times, but there is record of past eruptions

Can become active and erupt again after a “wake up” period

Example: Mt. Rainier

Extinct: No eruption within recorded

history Not expected to ever erupt

againExample: Mount Mazama (Crater

Lake)

Crater Lake

Mount Rainier• The most dangerous volcano in the US• The danger is mostly from lahars traveling

down river valleys at a speed of 25mph and destroying everything in its path

• 100,000 people live on the solidified mudflows of previous eruptions

Mount Rainier• The mountain is dangerously unstable, a tall,

steep heap of loose rock held together by the force of gravity and a cubic mile of glacier ice that could be melted or shaken loose

• Lahar flows average every 500 years and have gone as far as the Puget Sound lowlands (1 in 7 chance of it happening during your lifetime)

• Mount Rainier has erupted 4 times in the last 4000 years with the last eruption 200 years ago

VolcanoVideos

• http://video.nationalgeographic.com/video/player/environment/environment-natural-disasters/volcanoes/volcano-eruptions.html

• http://video.nationalgeographic.com/video/player/environment/environment-natural-disasters/volcanoes/volcano-lava.html

• http://video.nationalgeographic.com/video/player/environment/environment-natural-disasters/volcanoes/volcano-eruptions.html