Volcanoes

Chap 15

Lesson 2: Volcanoes

Open Ended

Write everything you know about volcanoes

Open Ended

What would you like to learn about volcanoes today?

Lesson Objective:

I can explain how volcanoes change the Earth's Surface

What is a Volcano?

• A vent in the Earth's crust where molten rock flows

• Magma= underground liquid/ molten rock

• Lava = above ground liquid/ molten rock

Multiple Choice

Molten rock above the ground is called

• Magma

• Lava

How do Volcanoes form?

• Movement of tectonic plates causes eruptions and volcanoes

• Shape the Earth's surface

• Make mountains, new crust, destroy forests / land

Convergent Plate Boundary Volcanoes

• The denser plate subducts and becomes molten rock/ magma

• The magma rises through the cracks in the crust

• a volcano is formed

Multiple Choice

Which type of crust is the densest and will subduct in a convergent boundary?

• Continental Crust

• Oceanic

Divergent Plate Boundary Volcanoes

• When plates separate, magma flows up

• Happens the most at Mid Ocean Ridges

HOT SPOTS

• Not all volcanoes occur at plate boundaries

• Tectonic plates move over magma plumes

• Plumes are convective currents of magma

• Hawaii is an example of this

Multiple Choice

Where do volcanoes NOT occur?

• Convergent plate boundaries

• Divergent plate boundaries

• Transform plate boundaries

• Hot Spots

Ring Of Fire

• An area in the Pacific that has a lot of volcanic and seismic activity

Multiple Choice

The United States is part of the Ring of fire

• True

• False

Volcanoes in the USA

• 60 potentially active Volcanoes in the USA!

• Mount Ranier, Mt. St. Helens, Hawaii, etc

• USGS monitors these

Volcano Types

• Shield: large, gentle slopes, basaltic lava

• Composite: large and steep sided, explosive eruptions

• Cinder Cones: small steep sided, erupt gas rich basaltic lava

Volcanic Eruptions

• Can be a gentle lava flow (think Hawaii)

• Can be explosive (Mount St. Helens 1980)

• Depends on the chemistry of the magma

Magma Chemistry

• Silica affects viscosity (how it flows)

• Low silica means it flows easier, fluid lava and makes basaltic rock, found at Mid ocean ridges and ocean hot spots (Hawaii)

• High viscosity flows like sticky toothpaste, makes rocks like rhyolite and andesite, found at subduction zones and continental hot spots (Mount. St. Helens)

Multiple Choice

What kind of magma SILICA content causes big, explosive volcanic eruptions?

• Low

• High

Magma Chemistry (Dissolved gases)

• Contributes to how explosive an eruption can be

• Water Vapor, Carbon Dioxide, Sulfur Dioxide

• As magma approaches the surface of the Earth, less pressure holding the gas in the magma

• Eruptions caused by the gas bubbles building and escaping.

• Explosions happen bc gas doesn't easily escape from high silica magma

Multiple Select

What 2 things determine how explosive a volcanic eruption is?

• Silica Content

• Sulfur Content

• Dissolved Gases

• Plate boundary

Effects of Volcanic eruptions

• Lava Flows: rarely deadly, but damaging

• Ash falls: particles of rock/glass, dangerous, heavy, affects air quality and climate

• Mudflows: heat can melt snow and ice on the summit mix with ash and cause a flowing river of mud called lahars

• Pyroclastic flows: fast moving avalanches of gas, ash and rock

Poll

Which of the volcanic effects do you think is most dangerous?

• Ash Fall

• Mudflow

• Pyroclastic flow

• Lava Flow

Poll

Which of the volcanic effects do you think are most damaging

• Ash Fall

• Mud flow

• Pyroclastic flow

• Lava Flow

Open Ended

Write 3 things you learned about volcanoes from this presentation

Open Ended

Do you have any questions left?