U n i t - 3 Volcanoes

magma: liquid rock underground lava: liquid rock that has escaped out of ground crater: hole near top where lava shoots or oozes out Volcano Vocabulary

tephra: rock/hardened lava that pops or explodes out pyroclastic flows: avalanche of hot rocks that travels up to 200 km/hr Volcano Vocabulary

Pressure builds as gases in magma try to escape Enough pressure and the volcano erupts Why Volcanoes Erupt

Lava Types: Silica – Rock or Metallic – Iron –Basaltic – Low Silica – Low Viscosity –Andesitic – Medium Silica – Medium Viscosity –Rhyolitic – High Silica – High Viscosity Lava Types Viscosity: How resistant to flow High Viscosity – thick – slow flow Low Viscosity – thin – fast flow

Type of lava:Lava Description: Basaltic lava ● Lava oozes out Type of Eruption: Gentle Eruption How it’s Built: Buildup of basaltic layers form a wide flat volcano Shield Volcanoes

Example Example: Found at weak spots in crust called “Hot Spots” Example: Mauna Loa, HI Shield Volcanoes

Type of lava:Lava Description: Andesitic Lava ● Type of Eruption: Explosive - Builds pressure & lava pops out How it’s Built: Lava cools in air making tephra Piles of tephra, short steep sides Cinder Cone Volcanoes

Example : Found at fault lines like in Nevada and Arizona

Cinder Cone Volcanoes Tephra

Sunset Crater – Flagstaff, AZ

Tephra Pictures

Type of lava:Lava Description: Rhyolitic Lava ● High Pressure Type of Eruption: When high pressure – violent eruptions When pressure released – non – violent eruptions How it’s Built: Has layers of tephra covered by lava Composite Volcanoes

Example: Occurs at Subduction Zones (one plate sinks beneath another) Example: Mt. St. Helens, Soufriere Hills Composite Volcanoes