1. Volcanoes & Plate Tectonics

2. What is a Volcano?
A volcano is a landform that is created by lava and/or pyroclastics
Pyroclastics are the solid materials that are ejected from a volcano
Magma is molten rock that is found BENEATH the earth’s surface
When magma reaches the surface it is called lava

4. When lava cools & hardens it forms solid rock called an igneous rock
Lava that is released during a volcanic eruption adds new rock to existing land and forms new islands – constructive force

5. Location of Volcanoes 600 active volcanoes on land, more underwater
Volcanoes occur in belts
Major volcanic belt in the Ring of Fire which rims the Pacific Ocean
Volcanic belts form along plate boundaries

6. Volcanoes at Divergent Boundaries
Divergent boundaries are also known as spreading centers
Lithospheric plates along the ocean floor spread apart and allow lava to move upward
This creates new oceanic crust
Some of the lava creates a volcanic cone that may rise above the water
Islands off the coast of Iceland

7. Volcanoes located within oceans extrude lava that is mafic
Mafic lava is thin and runny and is dark in color
Main rock that is created from mafic lava is basalt

8. Volcanoes at Convergent Boundaries
Volcanoes at convergent boundaries occur at subduction zones
2 types of subduction zones
Oceanic-continental convergence
Oceanic crust subducts beneath continental crust and begins to melt – creating magma
Magma slowly moves upward because it is less dense than the surrounding rock
When magma reaches the surface, a volcano is formed

10. Oceanic-oceanic convergence
Denser oceanic plate will be subducted creating a deep-ocean trench
Subducting plate will begin to melt creating magma
Magma moves upward and creates a chain of volcanic islands
This is known as a volcanic island arc
These occur km from the deep-ocean trench
Example: Aleutian Islands

13. Hot Spot Volcanoes
A hot spot is an area in the middle of a continental or oceanic plate where volcanism occurs
Not near a plate boundary
Created by mantle plumes
Areas of magma originating in the mantle
Magma moves its way up to the crust and reaches the surface through cracks
Hot spots do not move, plates move over them
Examples: Hawaii and Yellowstone

15. Volcanic Activity How Magma Reaches Earth’s Surface Volcanic Eruption
Magma rises because it is less dense than the surrounding rock
It flows upward through any crack in the rock
Volcanic Eruption
Gas is dissolved in the magma
Gas is under tremendous pressure
As magma rises to the surface, pressure decreases
The dissolved gases begin to separate and form bubbles

16. An eruption occurs when an opening develops in the crust
Gases rush out and carry magma with them

17. Inside a Volcano
Pocket beneath the volcano that holds the magma is the magma chamber
Tube that connects the magma chamber to the Earth’s surface is called the pipe
Magma and pyroclastics leave the volcano through an opening called the vent
The bowl-shaped area at the top of the volcano is the crater

18. Viscosity Viscosity is a fluid’s resistance to flow
Similar to thickness
Low viscosity fluids flow more easily than high viscosity fluids
The hotter a liquid, the less viscous it becomes

19. Type of Liquid
Viscosity
Water
Syrup
Shampoo

20. Characteristics of Magma
Magmas differ in viscosity
The hotter the magma, the more fluid the magma is
Silica Content
Material formed from oxygen and silicon
The more silica there is in magma, the thicker the magma will be

21. Types of Magma Type of Magma Silica Content Viscosity Basaltic 50%
Least
Andesitic
60%
Intermediate
Granitic
70%
Greatest

22. Types of Volcanic Eruptions
Silica content of magma helps determine whether the eruption is quiet or explosive

23. Quiet Eruptions Basaltic lava – thin and runny
2 types of lava in quiet eruptions
Pahoehoe: fast-moving, hot lava which resembles a braid or rope
Aa: slow-moving, cooler lava that forms jagged chunks

26. Explosive Eruptions
If magma is thick and sticky, a volcano erupts explosively
Lava gets stuck in the volcano causing pressure to build up
Explosion breaks lava into pieces – pyroclastics
Ash: smallest pieces
Cinders: pebble-sized particles
Bombs: range in size from a baseball to a car
Pyroclastic flow: highly heated mixture of pyroclastics moving down a volcano

29. Stages of a Volcano
Active – “live” volcano that is erupting or has shown signs that it will in the near future
Dormant – “sleeping” volcano that scientists expect to be active in the future
Extinct – “dead” volcano, unlikely to erupt again

30. Other Types of Volcanic Activity
Hot spring – superheated pool of water heated by a nearby body of magma

31. Geyser – fountain of water and steam that erupts from the ground

32. Geothermal energy – energy created by water heated by magma
Used in Iceland

33. Monitoring Volcanoes
Geologists can predict volcanic eruptions more successfully than earthquakes
Geologists monitor changes in elevation, gases from the volcano, and earthquakes

34. Volcano Hazards
Quiet Eruptions – lava pours out of the volcano setting everything in its path on fire
Explosive Eruptions – emits hot, burning clouds of ash and cinders/bombs

35. Volcanic Landforms 3 types of volcanoes Shield volcanoes
Wide, gently sloping mountains
Formed by thin, runny basaltic magma with a low viscosity
Located at divergent boundaries and hot spots
Example: Mauna Loa

37. Cinder cone volcano Steep, cone-shaped hill or mountain
Built from ejected lava fragments
Fragments are ejected and begin piling up, creating the cone shape
Example: Paricutin

39. Composite Volcano Tall, steep, symmetrical structure
Composed of alternating layers of lava flows and pyroclastic deposits
Example: Mt. St. Helen’s

41. Lava Plateau
Flat, level areas where lava flows have traveled far and cooled
Cooled lava flows pile up on one another

43. Caldera
Roughly circular depression created by the collapse of the empty vent and magma chamber
Greater than 1 km in diameter

46. Landforms from Magma Volcanic neck
Forms when magma hardens in the volcano’s pipe
Softer rock wears away around the pipe leaving the neck behind

48. Dike
When magma forces its way across rock layers and hardens

50. Sill
When magma squeezes its way between parallel rock layers

52. Batholith
When a large body of magma cools and hardens beneath the surface

55. Dome Mountain
When small bodies of rising magma are blocked by horizontal layers of rock
Magma forces its way up and bends the rock layers into a dome shape

57. Lahar
Volcanic mudflow generated during a volcanic eruption

58. Volcanoes in the Solar System
Volcanoes on Venus
Thousands of volcanoes
Largest volcano is Theia Mons
Mostly shield volcanoes

59. Volcanoes on Mars Shield volcanoes Cone-shaped volcanoes Lava flows
Olympus Mons
Largest mountain in the solar system
Shield volcano
Covers an area as large as Ohio

61. Volcanoes on Distant Moons
Io – moon of the planet Jupiter
Triton – moon of the planet Neptune