Holy Smokes!

A Volcano Primer

What we will learn

1. Plates move and cause major events.2. The effects of volcanic eruptions on

earth.3. Location of volcanic regions and why

they are found at those places.4. What hot spots are and

where they are formed.

What is a volcano?A volcano is a weak spot in the crust where magma comes out.Magma is molten mixture of rock-forming substances, gases, and water from the mantle.When magma reaches earth’s surface, it is called lava.When lava cools, it forms rock.

Volcanoes and plate boundaries

Ring of Fire- A major volcanic belt that is formed by many volcanoes that rim the Pacific Ocean.Volcanic belts form along the boundaries of Earth’s plates.

Most volcanoes form along diverging plate boundaries such as mid-ocean ridges and along converging plate boundaries where subduction takes place.Ex: Mount Etna formed near Eurasian and African plate boundaries.

The Ring of Fire

Diverging BoundariesVolcanoes form along mid-ocean ridges where plates diverge.Ridges are long underwater mtn. ranges that have a rift valley down the center.Lava pours out of cracks in ocean floor,

building new mtns.Volcanoes also form along

diverging plate boundaries on land.

Ex: There are several large volcanoes along the Great Rift Valley in East Africa.

Converging BoundariesMany volcanoes form near converging plate boundaries where oceanic plates return to the mantle.Volcanoes may form where 2 oceanic plates collide or where an oceanic plate collides with a continental plate.

Where 2 oceanic plates collide, subduction takes place and the older, denser plate sinks beneath a deep ocean trench into the mantle.

Converging boundaries (cont)Some of the rock above the subducting plate melts and forms magma. The magma is less dense than the rock around it, so it rises toward the surface, & eventually breaks through the ocean floor, and creates a volcano.

Quick Check- Do NOT look at your notes or book.

1. What’s the difference in magma and lava?

2. Why does magma rise when it is inside earth?

3. What is the ring of fire?4. Why do volcanoes form at

divergent plate boundaries?

Island Arc

An island arc is a string of volcanic islands.The curve of an island arc is the same curve as the trench beneath it. Ex; Japan, New Zealand, Indonesia, Philippines, Aleutians, and Caribbean islands.

Volcanoes also occur where an oceanic plate is subducted beneath a continental plate.This type of collision produced volcanoes of the Andes Mtns in South America and the volcanoes of the Pacific NW in the USA.

Hot SpotsA Hot Spot is an area where material from deep within the mantle rises and then melts, forming magma.A volcano forms above a hot spot when magma erupts through the crust and

reaches the surface.Some hot spots lie in the middle of plates far from any plate boundaries.A hot spot in the ocean floor can gradually form a series of volcaic mtns.

Examples of hot spots

Hawaiian islands formed one by one over millions of years as the Pacific plate drifted over a hot spot. Hot spots can also form under the

continents. Ex: Yellowstone National Park in Wyoming marks a hot spot under the North American plate.

Compare Hot Spot to Island Arc-What’s the difference?

Hot Spots

SummarizerWrite a ½ page summary answering these

questions.1. What is a volcano?2. Where are volcanoes formed?3. How did the volcanoes in the Andes Mtns

form?4. What is a hot spot and how does it

form?5. Why are volcanoes are

located in the ring of fire?

3 Basic Volcano shapes

Shape tells us something about how the volcano was formed.

1.Cinder Cone2.Shield3.Composite

Cone

1. Cinder Cone Volcano

Formed by Tephra (volcanic cinders, bit of solidified lava, and bits of rocks) thrown into the air during an eruption & then fall back down around the vent (volcanic opening) forming a steep-sided loosely packed volcano.

ExampleCinder Cone Volcano

Parícutin Volcano in Mexico is a great example of a cinder cone volcano.

Paracútin

On February 20, 1943, a Mexican farmer noticed that a hole in his cornfield that had been there for as long as he could remember was giving off smoke.Throughout the night, hot glowing cinders were thrown high into the air.In just a few days, a cinder cone several hundred meters high covered his cornfield.

2. Shield Volcano

Quiet eruptions of basaltic lava spread out in flat layers.

The buildup of these layers forms a broad volcano with gently sloping sides.

Shield Volcano

The shapes of these volcanoes reflect the fact that they are constructed of lava flows that erupted non-explosively. It is usually many times larger than a composite cone or cinder cone volcano.Mauna Kea volcano

picture from www.usgs.gov

Example of Shield Volcano

Mauna Loa

Mt. Kilauea Probably one of the world’s most active volcanoes.The eruption of Kilauea Volcano that began in 1983 continues at the cinder-and-spatter cone of Pu`u `O`o

Mt. KilaueaPicture from http://www.britannica.com/eb/art-89176/Hawaiis-Kilauea-is-an-active-volcano

3. Composite Volcano

This type of volcano is composed of explosively erupted pyroclastic materials layered with lava flows and volcanic debris.

An explosive period can release gas and ash, forming a tephra layer.Then, the eruption can switch to a quieter period, erupting lava over the top of the tephra layer.

Example of Composite Volcano

Mount St. Helen’sErupted in 198057 fatalitiesOver 7000 big game animals perished4 billion board feet of timber (enough to build about 300,000 two-bedroom homes) destroyedDestroyed 27 bridges, nearly 200 homes. Blast and lahars destroyed more than 185 miles of highways and roads and 15 miles of railways.

Example of Composite Volcano

Mount PinatuboErupted in 1991Killed 847 people 184 people injured10, 000 home destroyed and another 5,000 were damaged.The ash cloud took one year to spread around the globe, reducing global temperatures. This resulted in

Floods in 1993 along the Mississippi RiverDrought in Africa in 1993The US had its 3rd wettest & coldest winter on record.

Example of Composite Volcano

KrakatauOne of the most violent eruptions in recent times occurred on an island in the Sunda Straits near Indonesia in August of 1883.Krakatau, a volcano on the island, erupted with such force that the island disappeared.

Example of Composite Volcano Krakatau

Killed 36,000 people most were killed by a giant tsunamiDestroyed 160 villagesFine ashes from the eruption were carried by upper level winds as far away as New York City Volcanic dust lowered global temperatures for five years, this caused

Example of Composite Volcano Krakatau

Unusual sunsets and weather patterns for three years Evidence:

William Ashcroft’s paintings The Scream

What determines how explosive an eruption is?

Amount of trapped

gases

Amount of Water Vapor

Composition of Magma

1. Trapped Gases

Gases such as water vapor and carbon dioxide are trapped in magma by the pressure of the surrounding magma and rock.

Gas escapes easily from some magma during quiet eruptions.However, gas that builds up to high pressures eventually causes explosive eruptions.

2. Amount of Water Vapor

The magma at some convergent plate boundaries contains a lot of water vapor.This is because oceanic plate material and some of its water slide under other plate material at some convergent plate boundaries.The trapped water vapor in the magma can cause explosive eruptions.

3. Magma Composition

The composition (what it is made of) determines how explosive a volcano will be.

Magma CompositionBasaltic

Magma made of basalt is very fluid, allowing trapped gases to escape easily. Volcanoes with basaltic lava have quiet, non-explosive eruptions.

Magma Composition Basaltic

Volcanoes with basaltic lava produce:

underwater pillow lava formations

rock structures shaped like tubes, balloons, or pillows.

As pahoehoe (pa-HOY-hoy) lava cools, it forms a ropelike structure.

• If the same lava flows at a lower temperature, a stiff, slowly moving aa (AH-ah) lava forms.

Magma Composition Basaltic

ExamplesYou can find volcanoes with basaltic lava

Hawaiian Volcanoes, including

KilaueaMona Loa

IcelandHeimaeyHekla

Magma Composition Granitic Lava

Silica-rich, or granitic (also called rhyolite) magma produces explosive eruptions.

Silica-rich granitic magma is thick, and gas gets trapped inside, causing pressure to build up.

Magma Composition Granitic Lava

Some examples of granitic volcanoes are

Yellowstone Caldera It is a super voclano!

Katmai, AlaskaLast eruted in 1912.

“If it had erupted in a populated area…"The magnitude of the eruption can perhaps be best realized if one could imagine a similar outburst centered in New York City. All of Greater New York would be buried under from ten to fifteen feet of ash; Philadelphia would be covered by a foot of gray ash and would be in total darkness for sixty hours; Washington and Buffalo would receive a quarter of an inch of ash, with a shorter period of darkness. The sound of the explosion would be heard in Atlanta and St. Louis, and the fumes noticed as far away as Denver, San Antonio, and Jamaica."

Magma Composition Andesitic Lava

Volcanoes with andesitic magmas have violent, explosive eruptions.It often forms at convergent plate boundaries where one plate slides under the other.

Magma Composition Andesitic Lava

The word andesitic comes from the Andes, which are mountains located along the western edge of South America, where andesite rock is common.Many of the volcanoes encircling the Pacific Ocean also are made of andesite.

Magma Composition Andesitic Lava

Mount Pelee, MartiniqueFamous for the May 8, 1902 eruption which killed 29,000 people and destroyed the city of St. Pierre. This is the largest number of causalities for a volcanic eruption this century.

Mayon, PhillipinesIt is the most active volcano in the Philippines. Since 1616, Mayon has erupted 47 times. It’s 1814 eruption killed 1,600.

Volcanoes in a nutshell

Three volcano typesShape

Cinder Violent eruptions

CompositeViolent & quiet eruptions

ShieldQuiet Eruptions

Volcanoes in a nutshell

Three factors affect how violent an eruption will be

Water VaporMore water vapor = bigger explosion

Trapped GassesHow easily the gas escapes determines how violent the explosionEasy escape = quiet eruptionDifficult to escape = explosive eruption

Magma TypeBasaltic Magma = quiet explosion Granitic/Andesitic = violent eruptions

Resources used

Volcano Worldhttp://volcano.und.edu/

US Geologic Surveyhttp://www.usgs.gov/

Glencoe Earth Materials & Processes