•VOLCANOLOGY:

•The study of Volcanoes.

•Volcanolegist is one who studies volcanoes.

•VOLCANISM:

•Any activity dealing with magma moving toward or

on the surface of the earth.

•MAGMA:

•Is liquid rock that is less dense then the surrounding

rock.

•It comes to the surface because there is less pressure

being applied to then the surrounding rock.

Although temperature deep within the

Earth is very high, most of the rock is

solid due to the intense pressure.

When the pressure changes in an area,

and the rock is allowed to melt, magma

(or liquid rock) forms.

How Magma Forms

How Magma Forms

• Magma is a mixture of molten rock, suspended

mineral grains, and dissolved gases that fuels all

volcanoes.

• Magma forms when temperatures are high enough to melt the rocks involved, usually between 800°C and 1200°C.

• Such temperatures exist at the base of the lithosphere and in the asthenosphere.

Types of Magma• The 3 major types of magma are:

– Basaltic magma has the same composition as basalt and fuels the volcanoes that make up the Hawaiian Islands and Surtsey, which is south of Iceland.

– Andesitic magma has the same composition as andesiteand fuels Mount St. Helens in Washington State and Tambora in Indonesia.

– Rhyolitic magma has the same composition as granite and fueled the dormant volcanoes in Yellowstone National Park.

Types of Magma

Magma Composition

– Viscosity is the internal resistance to flow; the higher the viscosity, the thicker the magma.

Types of Magma

• The viscosity of magma and lava depends on both

temperature and composition.

– The hotter the magma or lava, the lower the viscosity.

– Magmas and lavas high in silica have higher viscosities than magmas and lavas low in silica.

Volcano Locations

Section Assessment

1. Match the magma types with their

characteristics.

___ Basaltic

___ Andesitic

___ Rhyolitic

A. intermediate viscosity content, forms from oceanic crust and oceanic sediments

B. low viscosity and gas content, forms from rocks in the upper mantle

C. high viscosity, forms from continental crust materials

B

A

C

Anatomy of a Volcano

• Magma that reaches Earth’s surface it is called Lava.

• A Vent is where lava erupts through an opening in the crust.

• As lava flows out onto the surface, it cools and solidifies around the vent, eventually accumulating to form a mountain known as a volcano.

• A Crater is a bowl-shaped depression at the top of a volcano that is connected to the magma chamber by a vent.

Anatomy of a Volcano• Volcanic craters are usually less than 1 km in diameter.

• Calderas, However, are large depressions up to 50 km in diameter that can form when the summit or the side of a volcano collapses into the magma chamber that once fueled the volcano.

Anatomy of a Volcano

Main Vent

Crater

Secondary

Vent

Magma Chamber

Lava Flow

Types of Volcanoes The appearance of a volcano depends on two factors:

Based on these two criteria, 3 major types of volcanoes have been identified:

– The type of material that forms the volcano

– The type of eruptions that occur

1. Shield volcanoes

2. Cinder-cone volcanoes

3. Composite volcanoes

Types of VolcanoesShield Volcanoes

– A Shield volcano is a mountain with broad, gently sloping sides and a nearly circular base that forms when layer upon layer of basaltic lava accumulates during nonexplosive eruptions.

Types of VolcanoesCinder-Cone Volcanoes

– A Cinder-Cone volcano is a generally small, steep-sided volcano that forms when material ejected high into the air falls back to Earth and piles up around the vent.

– The magma that fuels these volcanoes contains more water and silica than shield volcanoes, which makes them more explosive in nature.

Located just north of Flagstaff AZ,

Sunset Crater National Monument is

one of the best preserved volcanic

cinder cones in the United States. Of

the 800 volcanoes in the San Francisco

Peaks area, Sunset Crater is the most

recent location of volcanic activity in

this volcanic field of north central

Arizona. The primary eruptive event

that formed this cone was likely

observed by the “sinagua” or anasazi

native Americans in the year 1064.

These people are believed to have

moved to the nearby areas of Wupatki

and Walnut Canyon.

Frequently steep sided, cinder cones

are formed when volcanic tephra

builds up around an active vent. The

cinders also known as scoria are

typically basaltic lava with trapped

bubbles of volcanic gasses. Volcanic

cinders are usually black in color due

to high iron content. The cinders near

the top of Sunset Crater were exposed

to corrosive volcanic gasses that

accelerated the oxidation of the iron.

While exploring the southwest, Maj.

John Wesley Powell, observed that the

red and orange oxidized cinders

resembled the colors of a western

sunset and gave the mountain its name.

Types of VolcanoesComposite Volcanoes

– Composite volcanoes are large volcanoes that form when layers of volcanic fragments alternate with lava.

– The magma that forms composite volcanoes commonly contains large amounts of silica, water, and gases, making these volcanoes violently explosive.

Volcán Misti stands (19,101 ft) above sea level in southern Peru. The

extinct volcano is part of the Cordillera Occidental, an arm of the

Andes Mountains.

Volcanic Material• Tephra are rock fragments thrown into the air

during a volcanic eruption.

• Tephra are classified by size, the smallest being dust (less than 0.25 mm) and ash (0.25–2 mm).

• Somewhat larger fragments are called lapilli, or “little stones” (2–64 mm in diameter).

• The largest tephra thrown from a volcano include angular volcanic blocks and rounded or streamlined volcanic bombs, both of which can be the size of a house or larger.

Volcanic MaterialPyroclastic Flows

– A Pyroclastic Flow is a cloud of volcanic gas, dust, and other tephra traveling at speeds of nearly 200 km/h.

– The temperature at the center of a pyroclastic flow can exceed 700°C.

Pyroclastic Flow

Pahoehoe: Pronounced “pa-ho-ho”, this type of lava is

much thinner and less viscous than a’a. It can flow down

the slopes of a volcano in vast rivers. The surface of the

lava congeals into a thin crust that looks very smooth.

Pahoehoe erupts at temperatures of 1100 to 1200 C.

Volcanic MaterialTypes of Lava

A’a: Pronounced “ah-ah”, this is a basaltic lava that doesn’t

flow very quickly. It looks like a slowly moving mass of hot

jello, with cooler, rough surface. Once it hardens, the sharp

spiny surface of a’a lava is extremely difficult to walk across.

These types of lava erupt at temperatures above 1000 to 1100

degrees C.

Volcanic MaterialTypes of Lava

Mt. St. Helens

Mt. Pinatubo

Where do volcanoes occur?• Most volcanoes form at plate boundaries.

– About 80 percent of all volcanoes are found along convergent boundaries.

– About 15 percent are found along divergent boundaries.

– Only about 5 percent of extrusive igneous activity occurs far from plate boundaries.

Where do volcanoes occur?

Where do volcanoes occur?Hot Spots

– Some volcanoes are located far from plate boundaries and form as the result of hot spots.

– Hot spots are unusually hot regions of Earth’s mantle where high-temperature plumes of mantle material rise toward the surface.

– A plume does not move laterally, which results in a trail of progressively older volcanoes that formed as a plate moved over a hot spot.

Most volcanoes are associated with plate boundaries. Hotspots

are the exception.

You find hotspots in the middle of plates, weather that is in the

middle of a continental plate like Yellowstone or in the middle of

a oceanic plate like Hawaii

Where do volcanoes occur?Hot Spots

Where do volcanoes occur?Hot Spots

– The Hawaiian Islands continue to rise above the ocean floor as the Pacific Plate moves slowly over a hot spot.

– The rate and direction of plate motion can be calculated from the positions of volcanoes in a chain that has formed over a hot spot.

Mount Rainier the highest peak in the Cascade Range, which runs

through southwestern Canada and the northwestern United States.

The dormant, glacier-capped volcano rises to a height of (14,410 ft)

in western Washington. The mountain’s slopes support 25 named

glaciers, the thickest of which is the Carbon Glacier, at (705 ft).

Mount Fuji Japan- Highest Mountain in Japan

12,387 ft.

MT. Etna, Italy

Kilauea Volcano

Hollywood cannot compete

with the real thing - lava pouring

to the sea, an image that conjures

scenes from Dante's "Inferno".

Kilauea, the most active volcano

on Hawaii, has been erupting

constantly since 1983, drizzling

over 2 cubic kilometers of lava

across its flanks in a continual

island building process covering

over 100 square kilometers and

adding over 200 hectares to

Kilauea's southern shore. The

current flow started on Mother's

Day, May 12, when a new vent

opened near the southwest base of

Pu`u `O`o and has been inching

steadily toward the coast. In the

third week of July, the flow finally

reached the sea, and began

pouring into the ocean at a point

known as West Highcastle and

later at Wilipe`a. This view to the

west shows photographers on the

other side of the flow watching in

awe as the 1000+ degree C

magma pours into the ocean,

forming new land as a bench of

rock.

The Pu`u `O`o-Kupaianaha eruption of Kilauea, still continuing since it began in 1983, ranks as the most voluminous

outpouring of lava on the volcano's east rift zone in the past five centuries. By January 2000, 1.9 km3 of lava had

covered 102 km2 and added 205 hectares to Kilauea's southern shore. In the process, lava flows destroyed 181 houses

and resurfaced 13 km of highway with as much as 25 m of lava. Lava flows from Pu`u `O`o to the sea, sometimes

through lava tubes beneath the surface. When a portion of the ceiling of a lava tube collapses, a "skylight" is formed,

giving volcanologists a glimpse into the interior of the lava tube. The walls of the tube are so hot that they are nearly

indistinguishable from flowing lava in the bottom of the tube, raching temperatures of nearly 1200 degrees C.

The tallest mountain in Africa, Kilimanjaro, lies near the

border of Kenya. The mountain has two volcanic peaks,

spaced (7 miles) apart, with the higher of the two rising

(19,341 ft).

Mount Meru is an

active volcano

located just 70

kilometers(44

miles) west of

Mount

Kilimanjaro in

Tanzania. It

reaches 4,566

meters (14,978

feet) in height but

has lost much of

its bulk due to an

eastward volcanic

blast sometime in

its distant past,

perhaps similar to

the eruption of

Mount Saint

Helens in

Washington State

in 1980. Mount

Meru most

recently had a

minor eruption

about a century

ago.

The several small

cones and craters

seen in the vicinity

probably reflect

numerous episodes

of volcanic

activity.

Mount Meru is the

topographic

centerpiece of

Arusha National

Park, but

Ngurdoto Crater

to the east (image

top) is also

prominent. The

fertile slopes of

both volcanoes rise

above the

surrounding

savanna and

support a forest

that hosts diverse

wildlife, including

nearly 400 species

of birds, and also

monkeys and

leopards, while the

floor of Ngurdoto

Crater hosts herds

of elephants and

buffaloes.

The Deadliest Volcanic Eruption of the

century and perhaps the deadliest disaster in

the Western Hemisphere since 1900 occurred

on the Caribbean island of Martinique - the

northern most Windward Island of the Lesser

Antilles. Martinique is part of a volcanic arc of

islands, formed by the subduction of the North

American Plate beneath the Caribbean Plate.

When Pelee erupted on May 8, 1902, the coastal

town of St. Pierre, about 5 miles (8 km) to the

south of the Pelee, was virtually obliterated, as

shown on the above photo.

The approximately 29,000 inhabitants of St.

Pierre were killed by an incandescent, high-

velocity ash flow, sometimes referred to as a

nuees ardente (glowing cloud). Superheated gas

and steaming volcanic ash poured out of the

cone of Pelee and sped down its flanks. Within

minutes, a poisonous red cloud enveloped and

incinerated St. Pierre. The cloud was so dense

that very little sunlight was transmitted

through it - at noon it looked like midnight.

This is the same kind of eruption that buried

Pompeii after Vesuvius erupted in 79 A.D.

As a footnote to the eruption of Pelee 100 years

ago, it's reported that only one person survived

Pelee's fury; a prisoner in an underground cell.

World’s Deadliest Volcano Eruption

Mt. Pelee - May, 8, 1902

Popocatépetl, whose name is the Aztec

word for smoking mountain, towers 55

km to the east of Mexico City, Mexico

and is North America's 2nd highest

volcano rising 5,465 meters above sea

level. The steep-sided volcanic cone

came back to life six years ago after

nearly 70 years of dormancy and has

been erupting intermittently since then.

More than 30 million people live within

view of the volcano. On Monday,

December 18, the largest eruption of

Popocatépetl in 1,200 years occurred

and convinced people to leave

immediately. Over 56,000 evacuees of

the 40 villages within 12 km of the

volcano crowded the roads heading

away from the eruption. Besides

volcanic ash, a hazard at Popo is the

possibility of the eruptive material

melting glacial ice on the volcano and

causing a large mudflow or lahar. The

volcano has quieted since the 18th, but

scientists are keeping a close watch on

this waking giant. Popocatépetl, locally

called "Popo," is one of more than 400

active volcanoes surrounding the

Pacific Basin.

Popocatépetl, Volcano

Tambora is a stratovolcano, forming

the Sanggar peninsula of Sumbawa

Island. The diameter of the volcano at

sea-level is about 38 miles (60 km).

Prior to the 1815 eruption, the

volcano may have been as tall as

13,000 feet (4,000 m). The 1815

eruption formed a caldera about 4

miles (6 km) in diameter. The caldera

is 3,640 feet (1,110 m) deep.

The 1815 eruption of Tambora was

the largest eruption in historic time.

About 150 cubic kilometers of ash

were erupted (about 150 times more

than the 1980 eruption of Mount St.

Helens). Ash fell as far as 800 miles

(1,300 km) from the volcano. In

central Java and Kalimantan, 550

miles (900 km) from the eruption, one

centimeter of ash fell. The eruption

was 7. The eruption column reached a

height of about 28 miles (44 km). The

collapse of the eruption column

produced numerous pyroclastic flows.

As these hot pyroclastic flows reached

the ocean where they caused

additional explosions. During these

explosions, most of the fine-fraction of

the ash was removed. The eruption

formed a caldera. An estimated

92,000 people were killed by the

eruption. About 10,000 direct deaths

were caused by bomb impacts, tephra

fall, and pyroclastic flows. An

estimated 82,000 were killed

indirectly by the eruption by

starvation, disease, and hunger.

Worlds Largest Volcanic Eruption

Mt. Tambora, Sumbawa Island

The explosion equaled 3 million atomic bombs

Tambora contains the deepest caldera in the world

The World’s Highest Volcano

Mt. Ojos del Salado, Nevodos Chile

22,595 ft.

Mole Hill in Rockingham county

near Harrisonburg, Virginia is all

that remains of what may have

been the last active volcano in

Virginia. The igneous rocks that

form the core of the hill have been

age dated as 47 million years old,

considerably younger than the

other igneous rocks in the area,

and are the remnants of a conduit

of molten rock that fed a volcano

long since eroded away in the

heart of the Appalachians. Mole

Hill rock contains the mineral

olivine, typically formed at great

depth, and fragments of sandstone

torn from country rock far

beneath as the hot magma rose to

the surface. This modest bump

rising from the Shenandoah Valley

between the Allegheny Mountains

and Massanutten Mountain still

has a story to tell for those willing

to look at the rocks.

Mole Hill Volcano, Virginia

Jupiter’s Moon IoThe Voyager 1 spacecraft launched by the United States National Aeronautics and

Space Administration (NASA) photographed both hemispheres of Io, the innermost

moon of Jupiter, in 1979. The moon’s colors depict its many volcanoes and the large

lava flows and sulphur-dioxide snow resulting from Io’s tremendous volcanic activity.

During the three months between the photos of Io taken by Voyager 1 and Voyager 2,

the surface of the moon changed dramatically—some volcanos stopped erupting while

previously dormant volcanos became active.

Olympus MonsOlympus Mons, is the highest known mountain in the solar

system, rising 26 km or (16 miles) above the surrounding plain

and measuring 600 km (375 miles) across at the base. It is a

shield volcano, now extinct, that built up over millions of years is

due to successive eruptions.