Table of Contents

Volcanoes and Plate Tectonics

Volcanic Eruptions

Volcanic Landforms

Volcanoes

What is a volcano?

• A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth’s crust to the Earth's surface.

• The volcano includes the surrounding cone of erupted material.

• Magma vs Lava

vent

cone

Magma chamber

Conduit

Or

Pipe

Central vent Crater

Side vent

The Ring of Fire

The Ring of Fire is a belt of

volcanoes that circles the

Pacific Ocean. As with

most of Earth’s volcanoes,

these volcanoes form

along boundaries

of tectonic plates.

Volcanoes and Plate Tectonics

Volcanoes and Plate Tectonics

Volcanoes and Diverging Boundaries

Volcanoes will form along mid-ocean ridges. Along the rift valley lava pours out

of the cracks in the ocean floor. On land you can find them forming along the

Great Rift Valley in East Africa.

Volcanoes and Converging Boundaries

Volcanoes often form where two plates collide. At a deep ocean trench

(oceanic crusts) Water causes the magma to cool down which will then rise up

making a volcano. This forms an Island Arc, which follows the curve of the

trench. This also occurs where oceanic plates subduct under continental, like

South America and the Andes Mountains and Pacific Northwest/Mount Rainier

Volcanoes and Plate Tectonics

Volcanoes and Plate Tectonics

Hot Spot

The Hawaiian Islands have formed one by one as the Pacific plate drifts

slowly over a hot spot. This process has taken millions of years.

Due to the motion of the Pacific plate which of the Hawaiian Islands

Is the oldest and which is the youngest? Why?

Volcanic Eruptions

Inside a Volcano

A volcano is made up of many different parts.

What happens when a volcano erupts?

• Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface.

-Same principle as hot air rising, e.g. how a hot air balloon works

• When magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it as to how it erupts.

• Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption!

-Think about shaking a carbonated drink and then releasing the cap.

• Small amounts of gas and (or) low viscosity (runny) magma will form an effusive (QUIET) eruption

-Where the magma just trickles out of the volcano (lava flow).

Volcanic Eruptions

Magma Composition

Magma varies in composition. It is classified according to the amount of

silica it contains. The less silica that the magma contains, the more

easily it flows.

Effusive (Quiet) Eruptions

Effusive eruptions are

characterized by outpourings

of lava on to the ground.

Explosive Eruptions

Explosive volcanic eruptions can be catastrophic

Erupt 10’s-1000’s km3 of magma

Send ash clouds >25 km into the stratosphere

Have severe environmental and climatic effects

Hazardous!!! Above: Large eruption column and

ash cloud from an explosive

eruption at Mt Redoubt, Alaska

Explosive Eruptions cont.

Three products from an

explosive eruption

Ash fall

Pyroclastic flow

Pyroclastic surge

Pyroclastic flows on

Montserrat, buried

the capital city.

Pyroclastic flow

Lahars/Mud flows

Pyroclastic fall

Lava flow

Noxious Gas

Earthquakes

Volcanic Hazards

Pyroclastic Flow

For example, eruption of

Vesuvius in 79 AD

destroyed the city of

Pompeii

On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.

Pyroclastic Flow - direct impact

Volcanic Eruptions

Cascade Volcanoes

The Cascade volcanoes have formed as the Juan de Fuca plate sinks

beneath the North American plate.

Stages of Volcanic Activity

Active volcano; has had

at least one eruption

during the past 1,000 to

10,000 years and in the

future.

Dormant Volcano; an active

volcano that is not erupting but

should erupt again. It erupted

more than 10,000 years ago.

Stages of Volcanic Activity

Extinct volcanoes; a volcano that has not erupted nor will it erupt

because there is no lava flow, i.e.; Hawaiian Islands

Extinct volcano, Mount Bosavi,

On the New Guinea mainland

Volcanic Eruptions

Mt. Rainier

Mount Rainier is part of the Cascade volcanoes. All past eruptions of

Mount Rainier have included ash and lava.

How a Caldera Forms

A caldera is a hole left when a volcano

collapses.

What is happening in the sequence of

diagrams?

Volcanic Landforms

Volcanic Landforms

Volcanic Mountains

Lava from volcanoes cools and hardens to form lava plateaus and three types of

mountains.

Cinder cone volcanoes

• Steep cone shaped hill or small mountain.

• Magma has high silica content (thick and sticky)

• Produces ash, cinders and bombs.

• Hundreds of meters high.

Composite (Stratovolcano) volcanoes

• Silica content of magma can vary

• Lava flows and explosive eruptions can alternate.

• Tall, cone shaped mountains layers of lava and ash

• Thousands of meters tall…Mount Fuji and Mount St. Helens

Shield volcanoes

• Spots on Earth’s surface where lava has steadily flowed up

making a volcano of many hardened layers of lava

• Gently sloping mountain formed over a hot spot rising

thousands of meters up.

• Example; islands of Hawaii.

Lava plateaus

• Forms after millions of years

• Lava that flows from several long cracks

in an area

• Can travel far before cooling and

solidifying

Volcanic Landforms

Use the graphic organizer to compare and contrast two types of volcanoes.

Volcanic Landforms

Volcanic Necks, Dikes, and Sills

Magma that cools and hardens into rock before reaching the surface forms

volcanic necks, dikes, and sills.

Volcanic Landforms

Batholiths

Batholiths are common in the

western United States.