Introduction to Volcanoes Our Objectives Today I Can

Introduction to Volcanoes

Our Objectives Today I Can… • Describe the Anatomy of a Volcanoes • Explain the formation of a Volcanoes – Relates to Location • Identify the Possible Locations of Volcanoes – Relates to plate Boundaries • Identify Types of Volcanoes

Origin of the word: Volcano • The word 'volcano' comes from the little island of Vulcano in the Mediterranean Sea off Sicily. Centuries ago, the people living in this area believed that Vulcano was the chimney of the forge of Vulcan - the blacksmith of the Roman gods. They thought that the hot lava fragments and clouds of dust erupting form Vulcano came from Vulcan's forge as he beat out thunderbolts for Jupiter, king of the gods, and weapons for Mars, the god of war.

Anatomy of a Volcano

Anatomy of a Volcano: Caldera • Calderas are formed when the top of the volcano collapses

Anatomy of a Volcano: Caldera • Fissures are cracks or tears on or near volcanos where lava ma flow from.

Anatomy of a Volcano: Caldera • Lava Dome – as the magma is forced upward a protrusion forms on the volcano.

Anatomy of a Volcano: Caldera • Tephra – materials that are ejected from the volcano. They can be any size (as seen below).

Formation of Volcanoes • Rock melts deep in the earth forming magma • Magma is less dense than rock so it rises to the surfaces • Magma flows out through vents (openings on the surface) • Lava flows out of vents and begins to cool and becomes igneous rock • This process occurs year to year and the igneous rock continues to form from the cooling lava. Recall Unit 4: Intrusive vs. Extrusive Igneous Rock • The size of grain (crystal) depended on the rate of cooling.

Formation of Volcanoes

Location of Volcanoes • Divergent Plate Boundaries – Ex: Iceland which is located along the Mid-Atlantic Ridge • Convergent Plate Boundaries (subduction zones) – Ex: Mount St. Helen (WA) Mount Shasta (CA) – Magma forms when one plate slides beneath another plate and begins to melt – Magma is then forced to the surface • Hot Spots – Ex: Hawaiian islands – Formed by unusually hot magma that melts the earth’s crust

Location of Volcanoes

Location of Volcanoes • Divergent Plate Boundaries

Location of Volcanoes • Convergent Plate Boundaries

Location of Volcanoes • Hot Spots http: //www. wwnorton. com/colle ge/geo/egeo 2/content/animatio ns/2_6. htm – hot spot develop above hotter-than-usual areas of the mantle. • Magma generated by the hot spot rises through plates and produces active volcanoes at the Earth's surface. – As oceanic volcanoes move away from the hot spot, they cool and subside, producing older islands, atolls, and seamounts. • As continental volcanoes move away from the hot spot, they cool, subside, and become extinct.

Location of Volcanoes

Forms of Volcanoes Shield Volcanoes • Forms from the build up of quiet eruptions through vents or fissures – Resembles a warriors shield • Has gently sloping sides • Basaltic lava flows from here

Shield Volcanoes

Forms of Volcanoes Cinder Cone Volcanoes • Forms from the build up of explosive eruptions – Bits of rock called tephra are blown into the air and fall to the ground. Over time the sides of this volcano forms • Resembles a giant cone – Very steep side with loosely packed stone

Cinder Cone Volcanoes

Forms of Volcanoes Composite Volcanoes • Intermediate between cinder cone and shield volcanoes • Eruptions vary; some may be explosive others quiet (more next section) • Alternating layers of tephra and lava form the sides of the volcano • Found near subduction zones

Composite Volcanoes composite volcano

Composite Volcanoes

Forms of Volcanoes

More Volcano Types

Our Objectives Today were… Can I… • Describe the Anatomy of a Volcanoes • Explain the formation of a Volcanoes – Relates to Location • Identify the Possible Locations of Volcanoes – Relates to plate Boundaries • Identify Types of Volcanoes