VOLCANOES

CHAPTER 12

SECTION 1: VOLCANOES AND EARTH’S MOVING PLATES

HOW DO VOLCANOES AFFECT PEOPLE?

WHAT CONDITIONS CAUSE VOLCANOES TO FORM?

WHAT IS THE RELATIONSHIP BETWEEN VOLCANOES AND PLATES?

MOST ACTIVE VOLCANOES• Hawaii

• Kilauea (kee low AY ah) is the world’s most active volcano• May 1990 eruption destroyed the town of Kalapana

Gardens• Eruptions on and off since January 1983

• Iceland

• Hekla eruption February 2000• Iceland sits on an area where Earth’s plates more apart• Known as the island of fire and ice

EFFECTS OF ERUPTIONS

HUMAN

Evacuations occur with enough warning – people must leave their homes.

At times, everyone in the path is completely destroyed, homes, cars; towns are buried in ash.

ENVIRONMENTAL

Sulfurous gases from an eruption mix with water vapor to form acid rain.

Vegetation, lakes and streams are devastated by acid rain.

HOW DO VOLCANOES FORM?• Deep inside Earth, heat and pressure changes cause rock

to melt

• This magma is slowly forced upward toward the Earth’s surface

• After many, many years of this process, magma reaches the surface and flows out through an opening called a vent

• As the lava flows out and cools, it forms igneous rock around the vent. The steep walled depression around the volcano’s vent is the crater.

WHERE DO VOLCANOES OCCUR?

DIVERGENT BOUNDARIES• Plates moving apart

• Iceland is part of the Mid-Atlantic Ridge and located in the Artic Circle

• Plate separate forming rifts• Lava flows from the rifts and as it cools, builds layers of

rock• Sometimes, the eruptions rise above sea level, forming

new islands (like Iceland)• Island of Surtsey was formed in 1963

CONVERGENT BOUNDARIES• Plates move together

• Oceanic plates slide underneath continental plates

• Andes Mountains in South America• Volcanoes at convergent boundaries tend to erupt more

violently than others• Island of Monteserrat Volcano

• July 1995 • Destroyed towns, vegetation and killed people

HOT SPOTS• Hot rock at areas between Earth’s mantle and core is

forced toward the crust where it melts partially (this is NOT a plate boundary)

• Hawaiian Islands (p. 333 Figure 5)• Formed from volcanic activity over a period of 5 million

years• Five of the islands are volcanoes• Hot spot is stationary while the pacific plate moves

(causing the islands to actually change locations)

Formed through a series of violent volcanic eruptions, it is now a flooded crater.

HANAUMA BAY, HAWAII

A nature preserve popular among tourists for the beautiful coral reefs and wildlife

HANAUMA BAY, HAWAII

FOR TOMORROW

• Define “tephra” in your notes

• Read Section 2 pg. 336 – 343

• Bring a few colored pencils to diagram volcanoes!

SECTION 2TYPES OF VOLCANOES

HOW IS THE EXPLOSIVENESS OF A VOLCANIC ERUPTION RELATED TO THE SILICA AND WATER VAPOR CONTENT OF ITS MAGMA?

WHAT ARE THE THREE TYPES OF VOLCANOES?

ERUPTIONS

When you think about a volcanic eruption, what do you see in your head?

• Two major factors influence how an volcano erupts:

• Water Vapor & Trapped Gases Present in the Magma• Silica content in the magma

ERUPTIONS

TRAPPED GASES

Example: What happens when you shake a can of coke and then open it?

Gases can escape quietly or explode all at once, like a shaken Coke.

WATER VAPOR

At convergent plate boundaries, oceanic plates are involved.

The more water vapor present in the magma, the more explosive the eruption.

SILICA POOR MAGMAQUIET ERUPTIONS

• Basaltic Magma

• Fluid & quiet; lava pours from the vents and runs down the sides of the volcano

• Types of lava (pg. 338)

• Pahoehoe- rope like, smooth

• Aa- chunks of rocdk, shapr

• Pillow- pillow shape chunks, most common type.

SILICA RICH MAGMAEXPLOSIVE ERUPTIONS

• When plates slide underneath each other and the rock melts, the magma is forced upward

• Thick magma with lots of trapped gases

• Andesitic magma

• Granitic magma

TYPES OF VOLCANOES

SHIELD VOLCANO

• Broad volcano with sloping sides

• Example – Hawaiian Islands

• Basaltic Lava

• What type of eruption? • Can flow onto Earth’s surface through cracks

called fissures• Creates flood basalts, which is where most of the

material inside the volcano comes out at

SHIELD VOLCANO

CINDER CONE VOLCANO

• Steep sided, loosely packed

• Forms from tephra falling to the group from explosive volcanic eruptions

• Paricutin

• February 1943• Farmed noticed a large hole in his cornfield

suddenly had hot, glowing cinders in it. Over the next few days, cinders were thrown into the air from the opening, creating a cinder cone volcano

CINDER CONE VOLCANO

COMPOSITE VOLCANO

• Some volcanoes alternate between quiet and explosive eruptions

• Formed from a cycle of explosive and quiet eruptions, causing lava and tephra to layer on top of each other

• Found mostly where Earth’s plates come together

• Example – Mount Rainer in Washington

COMPOSITE VOLCANO

THREE TYPES OF VOLCANOES

UPCOMING

Section 1 & 2 Review Worksheet

Bill Nye “Volcanoes”

PROJECT RESEARCH DAY FRIDAY. You need to have chosen your volcano by Friday.

Section 3 –Monday

Test – Wednesday

PROJECTS DUE THURSDAY, 1/16 AND FRIDAY, 1/17.

SECTION 3IGNEOUS ROCK FEATURES

WHAT ARE IGNEOUS ROCK FEATURES AND HOW DO THEY FORM?

HOW DOES A VOLCANIC NECK AND A CALDERA FORM?