Volcanoes

1. Use this PowerPoint to help fill in your guided notes

2. We will paste these notes into our notebooks next week. Get a stamp and turn them in when you finish.

3. Return class copy of notes.

What is a Volcano?• Volcano is a term that refers

to:1. An opening in Earth’s crust

through which molten rock, ashes and gas erupt.

2. The structure that develops around the opening in Earth’s crust

Something to consider….what

would happen to the Earth if

there were NO VOLCANOES?

Three Types of Volcanoes• Shield volcano – LARGE• Composite-Strato volcano – MEDIUM• Cinder cones – SMALL

Shield Volcanoes• Have broad bases and gently sloping sides• Release lava slowly and can form huge

landmasses• Lava flows smoothly (is NOT viscous)– Ex. Mt. Loa, Hawaii

Composite-Strato Volcanoes (stratovolcanoes)

• Have steep sides and a narrower base.

• Erupt violently with hardened lava flow and pyroclastic material.

• Ex: Mt. Shasta• Lava is very viscous

(doesn’t flow well)

After a violent eruption, composite volcanoes may remain fairly quiet for a long time. Beneath the surface, magma and gases are building up for the next explosive

eruption

JUST FYI-read and rest your writing hand for a bit.

• A pyroclastic flow is a fluidized mixture of solid to semi-solid fragments and hot, expanding gases that flows down the flank of a volcanic edifice.

• They move much like a snow avalanche, except that they are fiercely hot, contain toxic gases, and move at phenomenal, hurricane-force speeds, often over 100 km/hour!!!

• They are the most deadly of all volcanic phenomena.

Cinder Cones• Smaller than other

types of volcanoes• Typically form in

groups on the sides of larger volcanoes

• Made of loose volcanic material, called cinders

• Ex: Sunset Crater

Classifying Volcanoes

• An active volcano is currently erupting or has erupted recently (in geological terms)

• A dormant volcano has not erupted lately but is considered likely to do so in the future.

• An extinct volcano has not erupted for a very long time and is considered unlikely to do so in the future.

Distribution of Volcanoes

• HOT SPOTS: Caused by a narrow stream of hot magma convecting up from the Earth‘s core-mantle boundary.

Tectonic plates move slowly across a fixed hot spot deep below the surface.

Volcanoes are found at• Convergent-Subduction boundaries• Divergent boundaries

Hot Spots

Volcanic chains like the Hawaiian Islands result from a hot spot under Oceanic plate.

Volcanic activity like Yellowstone park occurs from a hotspot under continental plate.

Calderas

Caldera- A bowl shaped depression formed when a volcano erupts, empties a magma chamber and then collapses on itself. (see diagram)

Great job!

• Please return your class copy and get a stamp from the teacher.

• Review the movie notes that you will answer on the back so that you know what to look for as you watch.

• Please be quiet and respectful of your classmates as they finish their own notes.

Local Volcanoes

Magma• Viscosity is resistance to flow.

• Rhyolitic Magma = High Viscosity =Slow Flowing Lava

• Basaltic Magma = Low Viscosity = Fast Flowing Lava

Types of Magma• Basaltic magmas form at rifts and at oceanic hot spots.• Andesitic magmas form at subduction boundaries.• Rhyolitic magmas form where hot spots underlie continental

plates.

PEP TALK!