VOLCANOES

What is a Volcano?What is a Volcano?

• A volcano is a weak spot in the crust where Magma, comes to the surface.

• Volcanic activity is a constructive force that adds new rock to existing land.

Where do volcanoes form?Where do volcanoes form?

• Volcanoes occur mostly along PLATE BOUNDARIES!

Ring of Fire

Belt of volcanoes that surrounds the Pacific Ocean

• Volcanoes form along the mid-ocean ridge,

• Rift valleys.

Divergent

ConvergentConvergent

• Volcanoes are also found at convergent boundaries• Ocean/Ocean collision• Ocean/Continental collision

The island of Hawaii is made up of 5 huge volcanoes of which Mauna Loa is the worlds largest mountain by volume, Mauna Kea is the worlds highest mountain measured from base to top (half of it happens to be underwater) and Kilauea which is the worlds most active volcano.

Hot Spots

PARTS OF A VOLCANOPARTS OF A VOLCANO

Magma ChamberMagma ChamberWhere magma collects beneath a volcano.

PIPEPIPE A long tube in the ground that connects the magma chamber to the surface.

PARTS OF A VOLCANOPARTS OF A VOLCANO

VENTVENT Any opening in a volcano.

CRATERCRATER A bowl shaped area that may form at the top of a volcano.

PIPE

CRATERCRATER

What are the two types of eruptions?

What are the two types of eruptions?

•EXPLOSIVE – ash is released

•QUIET – mostly lava released

Explosive

Quiet

Describe the important factors that affect the force of a volcanic

eruption?

Describe the important factors that affect the force of a volcanic

eruption?

• Dissolved Gases in magma

• Viscosity (thickness) of magma• Temperature of magma

• Composition of magma (silica content)

Factors Affecting Eruptions

10.1 The Nature of Volcanic Eruptions 10.1 The Nature of Volcanic Eruptions

Dissolved gases • Mainly water vapor and carbon dioxide

• Gases expand near the surface

• Molten rock and gases escape through vents in the volcano

Factors Affecting Eruptions

10.1 The Nature of Volcanic Eruptions 10.1 The Nature of Volcanic Eruptions

Viscosity• Factors affecting viscosity

- Temperature (hotter magmas are less viscous)

- Composition (silica content)

1. High silica—high viscosity (rhyolitic lava)

2. Low silica—more fluid (basaltic lava)

What is a pyroclastic flow?What is a pyroclastic flow?

• Pyroclastic flow occurs during an explosive eruption.

• It is composed of ash, cinders, bombs and gases.

LANDFORMS CREATED FROM LAVA

LANDFORMS CREATED FROM LAVA

• SHIELD VOLCANO

• CINDER CONE VOLCANO

• COMPOSITE VOLCANO

Profiles of Volcano TypesProfiles of Volcano Types

Shield VolcanoesShield Volcanoes• Low and broad in shape

•Have quiet eruptions

• Produce lava flows

• Produce very little pyroclastic debris

Mauna Loa— located on the big island of Hawaii, is a shield volcanoMauna Loa— located on the big island of Hawaii, is a shield volcano

Kilauea

Surtsey, Iceland

Cinder ConesCinder Cones

• Small volcano with single vent•Produces only explosive eruptions.•Has very steep slopes.

•They often look like an upside-down ice-cream cone.

Sunset Crater in Arizona

One of the largest cinder cone volcanoes in the United States

•Formed by alternating layers of lava and ash

•Very steep and jagged•Produces both quiet and explosive eruptions.

(They are the type of volcanoes that most likely come to mind when one usually thinks of a volcano. )

Composite or Stratovolcano

Mt. Fuji, Japan

Mt. RainerMt. Adams

Mt. Rainer

Mt. St. Helens before the eruption in 1980.

Mount St. Helens: May 19,1982 Mount St. Helens: May 19,1982 Before: 9,677ftBefore: 9,677ft :: After: 8,364 ft.After: 8,364 ft.

March 2013

Mount Hood, Oregon: Elevation 11,239 ft.

Mt. Lassen, California

Mt. Shasta, California

What are the stages of a Volcano?What are the stages of a Volcano?

• An active volcano is currently erupting or showing signs of erupting in the future.

• A dormant volcano is sleeping and may erupt in the future.

• An extinct volcano is dead. It is not likely to erupt again.

More LAVA LandformsMore LAVA Landforms

CalderasCalderas

• Large depressions in volcanoes formed by collapse

• Nearly circular

• Size exceeds 100 km in diameter

Crater Lake is a caldera that formed when Mt. Mazama collapsed 7,000 years ago.

Crater Lake, Oregon

Wizard island is a small cinder cone that formed after the collapse of Mt.

Mazama.

Wizard island is a small cinder cone that formed after the collapse of Mt.

Mazama.

Wizard Island in Crater Lake

Lava PlateausLava Plateaus• Fluid basaltic

lava extruded from crustal fractures called fissures.

• Layers and layers of lava build up over millions of years