1. Volcanoes

2. Volcanic Activity

3. Stages of a Volcano Active: Erupting or showing signs of an eruption in the near future Dormant: volcano not currently erupting but is expected to become active in the future Extinct: dead volcano unlikely to erupt again

4. Inside a Volcano Magma Chamber – pocket of magma beneath a volcano Pipe – narrow vertical crack through the crust that connect the magma chamber to Earth’s surface Vent – Where molten rock and gas escape the volcano (usually on the top) Crater – bowl shaped area that forms around a volcanoes vent

6. Characteristics of Magma 1. The hotter it is the more fluid it is 2. The more dissolved gases in magma the more explosive the eruption 3. The more Silica magma contains the thicker and stickier it is *** The Silica content of magma helps determine whether the volcanic eruption is quiet or explosive a. High Silica: light colored lava that is very sticky (viscous) Ex. Mt St. Helens b. Low Silica: dark colored magma that flows readily Ex. Mauna Loa, Hawaii

7. Magma Composition

8. Quiet Eruptions Due to a low silica content Lava Plateau – Eruption of lava forming a high level plateau covering a large geographic region Fissure Eruptions – Curtains of fire Shield Volcanoes –Wide gently sloping mountain made by layers of lava and formed by quiet eruptions. Ex. Mauna Loa, HI Pahoehoe lava – fast moving lava that forms a wrinkled surface Aa lava – slow moving lava that hardens into jagged chunks

9. Lava Plateau Eruption of lava forming a high level area Ex. Columbia Plateau

10. Fissure Eruption – Curtain of Fire

11. Shield Volcano Wide gently sloping mountain made by layers of lava and formed by quiet eruptions. Ex. Mauna Loa, HI

12. Pahoehoe Aa

13. Explosive Eruptions Due to a High Silica Content and trapped gases Ex. Krakatau & Mt. St. Helen Pyroclastic Flows: hot, fast moving, dense flow of ash, gases, and pyroclastics Different Types: Composite volcanoes Cinder cones Calderas

14. Composite Volcano Tall cone shaped mountain in which layers of lava alternate with layers of ash and other volcanic materials. Ex. Mt. St.Helen AKA – Strato volcano

15. Cinder Cone Volcano Small, steep cone shaped hill or mountain

16. Caldera Large hole at the top of a volcano formed when the roof of a volcano’s magma chamber collapses. Ex. Crater Lake,OR

18. Other Types of Volcanic Activity Hot springs Geysers

19. Volcanic Landforms

20. Landforms formed from Magma Volcanic Neck – formed when magma hardens in a volcano’s pipe Dike – formed when magma is forced across rock layers hardens Sill – formed when magma squeezed between rock layers hardens Batholith - mass of rock formed when a large body of magma cools within the crust. Ex. Half Dome, Yosemite National Park, CA These are INTRUSIVE landforms

21. Shiprock, NM Neck Dike

22. Sill

23. Batholith Half Dome, Yosemite National Park

24. Volcanoes & Plate Tectonics

25. Volcano A weak spot on the Earth’s crust where molten material comes to the surface (volcanic activity = constructive force) Magma – molten mixture of rock, gases, and water from the mantle (underground) Lava – magma that has reached the surface

26. Location of volcanoes Most volcanoes occur at Subduction zones (trenches) and divergent plate boundaries (mid-ocean ridge) Plate Boundaries!! Ring of Fire – major belt of volcanoes around the rim of the Pacific Ocean

28. Volcanoes at Subduction Zones Ocean – Continent = volcanic coastal mountain range, ex. Andes and Cascade Mountains Ocean – Ocean = Volcanic Island Arc: string of islands formed by volcanoes produced at a deep ocean trench, Ex. Aleutian Islands & Indonesia

29. Volcanic Island Arc: Aleutian Islands

30. Volcanoes at Divergent boundaries Mid-ocean ridge: where magma erupts and pushes older ocean floor outward

31. Hot Spot Volcanoes An area within a plate where magma from deep in the mantle melts through the crust above it Ex. Hawaiian Islands & Yellowstone Viscosity - the property of resistance to flow in a fluid or semifluid less viscous = honey more viscous =peanut butter

32. Hot Spot Volcanoes