Table of Contents Volcanoes and Plate Tectonics Volcanic Eruptions Volcanic Landforms Volcanoes
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Table of Contents
Volcanoes and Plate Tectonics
Volcanic Eruptions
Volcanic Landforms
Volcanoes
What is a volcano?
• A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth’s crust to the Earth's surface.
• The volcano includes the surrounding cone of erupted material.
• Magma vs Lava
vent
cone
Magma chamber
Conduit
Or
Pipe
Central vent Crater
Side vent
The Ring of Fire
The Ring of Fire is a belt of
volcanoes that circles the
Pacific Ocean. As with
most of Earth’s volcanoes,
these volcanoes form
along boundaries
of tectonic plates.
Volcanoes and Plate Tectonics
Volcanoes and Plate Tectonics
Volcanoes and Diverging Boundaries
Volcanoes will form along mid-ocean ridges. Along the rift valley lava pours out
of the cracks in the ocean floor. On land you can find them forming along the
Great Rift Valley in East Africa.
Volcanoes and Converging Boundaries
Volcanoes often form where two plates collide. At a deep ocean trench
(oceanic crusts) Water causes the magma to cool down which will then rise up
making a volcano. This forms an Island Arc, which follows the curve of the
trench. This also occurs where oceanic plates subduct under continental, like
South America and the Andes Mountains and Pacific Northwest/Mount Rainier
Volcanoes and Plate Tectonics
Volcanoes and Plate Tectonics
Hot Spot
The Hawaiian Islands have formed one by one as the Pacific plate drifts
slowly over a hot spot. This process has taken millions of years.
Due to the motion of the Pacific plate which of the Hawaiian Islands
Is the oldest and which is the youngest? Why?
Volcanic Eruptions
Inside a Volcano
A volcano is made up of many different parts.
What happens when a volcano erupts?
• Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface.
-Same principle as hot air rising, e.g. how a hot air balloon works
• When magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it as to how it erupts.
• Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption!
-Think about shaking a carbonated drink and then releasing the cap.
• Small amounts of gas and (or) low viscosity (runny) magma will form an effusive (QUIET) eruption
-Where the magma just trickles out of the volcano (lava flow).
Volcanic Eruptions
Magma Composition
Magma varies in composition. It is classified according to the amount of
silica it contains. The less silica that the magma contains, the more
easily it flows.
Effusive (Quiet) Eruptions
Effusive eruptions are
characterized by outpourings
of lava on to the ground.
Explosive Eruptions
Explosive volcanic eruptions can be catastrophic
Erupt 10’s-1000’s km3 of magma
Send ash clouds >25 km into the stratosphere
Have severe environmental and climatic effects
Hazardous!!! Above: Large eruption column and
ash cloud from an explosive
eruption at Mt Redoubt, Alaska
Explosive Eruptions cont.
Three products from an
explosive eruption
Ash fall
Pyroclastic flow
Pyroclastic surge
Pyroclastic flows on
Montserrat, buried
the capital city.
Pyroclastic flow
Lahars/Mud flows
Pyroclastic fall
Lava flow
Noxious Gas
Earthquakes
Volcanic Hazards
Pyroclastic Flow
For example, eruption of
Vesuvius in 79 AD
destroyed the city of
Pompeii
On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.
Pyroclastic Flow - direct impact
Volcanic Eruptions
Cascade Volcanoes
The Cascade volcanoes have formed as the Juan de Fuca plate sinks
beneath the North American plate.
Stages of Volcanic Activity
Active volcano; has had
at least one eruption
during the past 1,000 to
10,000 years and in the
future.
Dormant Volcano; an active
volcano that is not erupting but
should erupt again. It erupted
more than 10,000 years ago.
Stages of Volcanic Activity
Extinct volcanoes; a volcano that has not erupted nor will it erupt
because there is no lava flow, i.e.; Hawaiian Islands
Extinct volcano, Mount Bosavi,
On the New Guinea mainland
Volcanic Eruptions
Mt. Rainier
Mount Rainier is part of the Cascade volcanoes. All past eruptions of
Mount Rainier have included ash and lava.
How a Caldera Forms
A caldera is a hole left when a volcano
collapses.
What is happening in the sequence of
diagrams?
Volcanic Landforms
Volcanic Landforms
Volcanic Mountains
Lava from volcanoes cools and hardens to form lava plateaus and three types of
mountains.
Cinder cone volcanoes
• Steep cone shaped hill or small mountain.
• Magma has high silica content (thick and sticky)
• Produces ash, cinders and bombs.
• Hundreds of meters high.
Composite (Stratovolcano) volcanoes
• Silica content of magma can vary
• Lava flows and explosive eruptions can alternate.
• Tall, cone shaped mountains layers of lava and ash
• Thousands of meters tall…Mount Fuji and Mount St. Helens
Shield volcanoes
• Spots on Earth’s surface where lava has steadily flowed up
making a volcano of many hardened layers of lava
• Gently sloping mountain formed over a hot spot rising
thousands of meters up.
• Example; islands of Hawaii.
Lava plateaus
• Forms after millions of years
• Lava that flows from several long cracks
in an area
• Can travel far before cooling and
solidifying
Volcanic Landforms
Use the graphic organizer to compare and contrast two types of volcanoes.
Volcanic Landforms
Volcanic Necks, Dikes, and Sills
Magma that cools and hardens into rock before reaching the surface forms
volcanic necks, dikes, and sills.
Volcanic Landforms
Batholiths
Batholiths are common in the
western United States.
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