How Magma Reaches the How Magma Reaches the SurfaceSurface

Magma forms in the (asthenosphere) mantle. Magma forms in the (asthenosphere) mantle.

Magma is less dense than solid material so it rises toward the surface.Magma is less dense than solid material so it rises toward the surface.

When a volcano erupts, dissolved gases form bubbles that rush out, When a volcano erupts, dissolved gases form bubbles that rush out, taking the magma with them (like opening a can of soda pop)taking the magma with them (like opening a can of soda pop)

the magma with them. Like When a volcano the magma with them. Like When a volcano Reaches Earths Reaches Earths SurfaceSurface

Inside a VolcanoInside a Volcano Pipe: a long tube in the Pipe: a long tube in the

ground that connects the ground that connects the chamber to the Earth’s chamber to the Earth’s surface.surface.

Vent: where magma, and gas Vent: where magma, and gas leave the volcano.leave the volcano.

Lava flow: the river of lava Lava flow: the river of lava that comes out and over the that comes out and over the land.land.

Lava: Magma that reaches Lava: Magma that reaches the surface is calledthe surface is called lava.lava.

Crater: a bowl-shaped area Crater: a bowl-shaped area that forms around the vent.that forms around the vent.

Magma chamber: collects in Magma chamber: collects in pockets beneath the pockets beneath the volcano.volcano.

Characteristics of MagmaCharacteristics of Magma

The force of an eruption depends on four things……The force of an eruption depends on four things…… Amount of gas in magmaAmount of gas in magma How thick or thin the magma isHow thick or thin the magma is Its temperatureIts temperature Silica contentSilica content

Silica also determines how easily the magma flows.Silica also determines how easily the magma flows. More silica = thicker and lighter colored lava = stickyMore silica = thicker and lighter colored lava = sticky

Makes obsidian and Rhyolite and pumiceMakes obsidian and Rhyolite and pumice

Less Silica = darker colored lava + flows easilyLess Silica = darker colored lava + flows easily Makes basalt Makes basalt

Types of Volcanic EruptionsTypes of Volcanic Eruptions Quiet EruptionsQuiet Eruptions Magma is thin and flows easilyMagma is thin and flows easily

Pahoehoe: is a fast-moving Pahoehoe: is a fast-moving hot lava, mass of wrinkles, hot lava, mass of wrinkles, billows and ropelike coils billows and ropelike coils when it hardens.when it hardens.

AA: is a slow moving cool AA: is a slow moving cool lava, rough and jagged when it lava, rough and jagged when it hardenshardens

Explosive Eruptions- thick Explosive Eruptions- thick magma, pipe gets plugged and magma, pipe gets plugged and explodes when pressure builds explodes when pressure builds up.up.

Causes pyroclastic flow Causes pyroclastic flow explosive eruption hurls out explosive eruption hurls out gas, ash (sand-like), cinders gas, ash (sand-like), cinders (pebble sized), and bombs (pebble sized), and bombs (larger pieces, ranging from (larger pieces, ranging from baseball to car sized).baseball to car sized).

Stages of a VolcanoStages of a Volcano

1.1. Active or live volcano that is erupting or Active or live volcano that is erupting or shows signs that it erupt in the near shows signs that it erupt in the near future.future.

2.2. Dormant or sleeping – scientists expect Dormant or sleeping – scientists expect the volcano to erupt in the future and the volcano to erupt in the future and become active.become active.

3.3. Extinct or dead is unlikely to erupt again.Extinct or dead is unlikely to erupt again.

Volcanic LandformsVolcanic Landforms

Landforms from Lava & AshLandforms from Lava & Ash

A. Shield VolcanoesA. Shield Volcanoes

B. Cinder Cone VolcanoesB. Cinder Cone Volcanoes

C. Composite VolcanoesC. Composite Volcanoes

D. Lava PlateausD. Lava Plateaus

E. CalderasE. Calderas

Shield VolcanoesShield Volcanoes Thin layers of lava Thin layers of lava

pour out of a vent and pour out of a vent and harden on top of harden on top of previous layers.previous layers.

Build a wide, gently Build a wide, gently sloping mountain.sloping mountain.

Hawaiian Islands are Hawaiian Islands are shield volcanoes over shield volcanoes over a hot spot.a hot spot.

                                  

        

                                       

   

Mauna Loa, HawaiiMauna Loa, Hawaii

Cinder Cone VolcanoesCinder Cone Volcanoes

A steep, cone-shaped A steep, cone-shaped hill or mountain.hill or mountain.

Ash, cinders, and Ash, cinders, and bombs pile up around bombs pile up around the vent.the vent.

Cinders erupt Cinders erupt explosively.explosively.

Sunset crater is an Sunset crater is an example.example.

Composite VolcanoesComposite Volcanoes A steep, cone-shaped A steep, cone-shaped

volcano built up of volcano built up of layers and of rock layers and of rock fragments.fragments.

Steep at the top, flatens Steep at the top, flatens at the bottomat the bottom

Magma- high in silica, Magma- high in silica, making it pasty.making it pasty.

Erupt explosively.Erupt explosively. Mount St. Helens and Mount St. Helens and

Mount Rainier are Mount Rainier are examples.examples.

St. Augustine volcano, Alaska. St. Augustine volcano, Alaska.

Lava PlateausLava Plateaus

Continued eruptions Continued eruptions form high, level form high, level areas.areas.

Lava flows out of Lava flows out of several long cracks, several long cracks, and after millions of and after millions of years, these layers years, these layers form high plateaus.form high plateaus.

Example: Columbia Example: Columbia PlateauPlateau

Columbia PlateauColumbia Plateau

CalderasCalderas A huge eruption may empty the main vent A huge eruption may empty the main vent

and the magma chamber beneath the and the magma chamber beneath the volcano.volcano.

Mountain becomes a hollow shell and the Mountain becomes a hollow shell and the top collapses in.top collapses in.

Huge hole left is called a caldera.Huge hole left is called a caldera. Example: Crater Lake, OregonExample: Crater Lake, Oregon

Poas Volcano, Poas Volcano,

Costa RicaCosta Rica

Crater Lake, Crater Lake,

OregonOregon

Volcano HazardsVolcano Hazards Mount St. Helens erupted in 1980 after 123 Mount St. Helens erupted in 1980 after 123

years of being dormant. Before that people years of being dormant. Before that people viewed it as a peaceful mountain.viewed it as a peaceful mountain.

Quiet eruption hazards- lava flows from vents, Quiet eruption hazards- lava flows from vents, burning everything in their path.burning everything in their path.

Explosive eruption hazards- volcano will send Explosive eruption hazards- volcano will send out burning clouds of volcanic gases, cinders out burning clouds of volcanic gases, cinders and bombs.and bombs.

Volcanic ash can bury entire towns, damage Volcanic ash can bury entire towns, damage crops and clog car engines. Wet ash can cause crops and clog car engines. Wet ash can cause roofs to collapse and plane engines to stallroofs to collapse and plane engines to stall..