Locations of Volcanoes About 80% of volcanoes form at convergent plate boundaries About 20% of volcanos form at divergent plate boundaries. Hotspots: Occurs when a mass of hotter than normal mantle material (mantle plume) rises toward the surface. (There have been 40 hotspots identified.) Ring of Fire: The area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean.

Magma All volcanos are fueled by magma In order to create magma, you must have temperature, pressure, and water

Magma vs. Lava Viscosity: resistance to flow

Viscosity: resistance to flow Viscous – thick, slow moving , typically cooler temperature Less Viscous – thin, fast moving, typically hotter temperature Viscosity depends on two factors: Temperature (the cooler it is, more viscosity.) Composition (higher the silica content, more viscosity)

Anatomy of a Volcano Neck: channels magma to crater Vent: where magma reaches the surface Crater / Caldera: bowl shaped depression that forms around the vent Magma Chamber: storage chamber for magma, feeds magma to vent or neck neck –

Types of volcanoes – shield Gently sloping sides, circular base Formed by layer upon layer of basaltic lava Nonexplosive Kohala, Hawaii

Types of volcanoes – cinder cone Steep sides, cone shape Have water and silica content in magma Ejected material piles up around vent Arizona

Types of volcanos – composite / Stratovolcano Largest type Larger amounts of silica, water and gas Violent, explosive nature Mt. Fuji, Japan

Volcanic Material Lava Flow – flow of lava

Volcanic Material Lava Flow – flow of lava Pyroclastic Flow – mixture of clouds of gas, ash, and rock fragments (can travel up to 200km/hr)

Volcanic Material Lava Flow – flow of lava Pyroclastic Flow – mixture of clouds of gas, ash, and rock fragments (can travel up to 200km/hr) Ash Cloud – thin ash particles ejected into the atmosphere

1,500 active volcanoes on earth

Intrusive magma formations The structures that result from the cooling and hardening of magma at depth are called plutons. All plutons form beneath earths surface Uplifting and erosion expose them

Looking Glass Rock, NC One of the largest masses of granite in the Eastern United States

Types of Igneous formations Laccoliths – viscous magma that has collected, and intruded close to the surface Looks like a mushroom Batholith

Types of Igneous formations Sills – forms when magma is intruded close to the surface Looks like horizontal lava flows Batholith

Types of Igneous formations Dikes – form when magma is injected into fractures Cuts across preexisting rock layers Batholith

Types of Igneous formations Batholiths – forms from cooled magma chambers Largest intrusive formation Batholith