Section 6.1• Vocabulary to know: • Volcano

• Quiet eruptions• Explosive eruptions• Crater• Central vent• Dike• Lava• Pipe • Magma chamber• Magma• Aa• Pahoehoe• Pillow lava• Blocky lava• Pyroclastic• Volcanic bombs• Lapilli• Volcanic ash• Volcanic blocks

What is a Volcano?

• Volcano- – a

mountain that forms when magma (As well as volcanic gases) reaches the surface

How do volcanoes form?Magma reaches the surface through a vent

Explosive eruption. Boiling mud and ash are hurled into the air

Hot lava then flows out through the vent. The lava cools and hardens

The process keeps on repeating itself making the volcano grow larger

Types of Eruptions• Quiet (Non explosive)

eruptions- – Have very hot, low

silica, low viscosity magma

• Explosive eruptions- – High amounts of water– High silica, and high

viscosity magma• Clogs a volcanic pipe…• Enormous pressure

builds up…• Steam gets trapped…• Volcano explodes!!!

Non explosive volcanic eruptions• 4 different types of lava:

Aa- forms brittle crust…crust gets torn into little pieces as lava flows underneath

Pahoehoe- flows very slowly…like wax dripping from a candle

Pillow lava- forms when eruptions occur underwater

Blocky lava- cool and stiff. Doesn’t travel far from the erupting vent of the volcano

Volcano Structure1. Crater-

• bowl shaped pit at top of central vent

2. Central vent- • magma escapes to the

surface3. Dike-

• leads to side vent

4. Lava- • magma that has reached the

surface

5. Pipe- • narrow vertical channel

6. Magma chamber- • pocket where magma

collects

Explosive volcanic eruptions• Produce pyroclastic material-

– Forms when magma explodes from a volcano and solidifies in the air

– 4 types:

Volcanic bombs-

•Large blobs of magma that harden in the air

Lapilli-

•Pebble-like bits of magma that harden before they hit the ground

Volcanic ash-

•Majority of pyroclastic material

Volcanic blocks-

•Solid pieces of rock erupted from volcano

What are pyroclastic flows?• Pyroclastic flow-

– Very dangerous– produced when

enormous amounts of hot ash, dust, and gases are ejected from volcano

– can race downhill at speeds of more than 200 km/h

– temperature at the center can exceed 700°C

Section 6.2

• Vocabulary to know: • Shield volcano• Cinder cone volcano• Composite volcano

Shapes of Volcanoes• Shield

volcano:– Broad– Gently

sloping

• Eruptions:– Hot, flowing

basaltic lava.– Travels a

long way before it solidifies

Mount Kilauea (Shield Volcano)

• Located in Hawaii• Presently the most active

volcano on the planet• Can be walked up to

because of its non-violent explosions

Shapes of Volcanoes• Cinder cone

volcano:– Small– Steep sides

• Form from:– Ash and

cinders that are ejected into the air and fall back onto the volcano

Shapes of Volcanoes• Composite

volcano:– Tall– Steep sides

• Built up from viscous lava, ash, and volcanic bombs

• Eruptions:– High silica– High viscosity

Mount St. Helens

• Composite volcano• Erupted on May 18,

1980• Killed over 55 people• Blast removed 1000 ft off

the top of the volcano• The explosion could be

heard as far away as Canada

• Notice the trees…

Krakatau

• Composite volcano• Erupted on August 26, 1883

in Indonesia• Explosions were heard 2200

miles away in Australia• Ash was propelled 50 miles

into the air– This ash blocked the sunlight

for 2 ½ days

• Created a tsunami 120 feet tall

• Killed 36,000 people

Mount Vesuvius

• Composite volcano• Erupted in Pompeii in 79

AD• 10 feet of ash piled on

top of the buildings after the explosion

• Considered to be one of the most dangerous volcanoes in the world– 3,000,000 people live

close to it

Mount Pinatubo• Erupted in 1991• A 7.7 Richter scale

earthquake caused the volcanic eruption

• Scientists predicted the eruption, and the residents were evacuated

• Caused the entire world’s temperatures to drop by 1 degree

Section 6.3

• Vocabulary to know • Plate boundary• Ring of fire• Divergent boundary• Convergent boundary• Hot spot

Most Volcanoes Occur at Plate Boundaries

Ring of Fire• Mostly

found along the edge of the Pacific plate

• Contains nearly 75% of the worlds active volcanoes found on land

Divergent Boundary• Magma

escapes to the surface as the plates move apart– Magma rises

to fill the gap between the two separating plates

– Mid ocean Ridge

Convergent Boundary• Oceanic plate is

subducted into the mantle…

• This causes melting…

• Magma forms and rises to the surface…

• Volcano created!!!• Why does the

magma rise?– It’s less dense

than the rocks around it.

Hot Spot• Hot spot stays

in one place…• Plates move

over the top of it…

• Over time, a chain of volcanoes is formed!!!

• Is Kauai an active volcano?

Iceland• Above sea level

because there is a hot spot that works with the mid ocean ridge

• What rocks would be the oldest?

• What would happen to a house built on the mid ocean ridge?