Post on 21-Dec-2015
E3.P3XC Unit: Volcanoes
Powerpoint on the standards for Volcanoes
Volcanic Eruptions• Volcano- mountain formed from molten
magma forced through the Earth’s surface• Magma- Molten rock material
Do you think that most volcanoes have explosive or non-explosive eruptions? Why?
• Most volcanic eruptions are Non-Explosive!
• Types of Eruptions– Non-Explosive• Lava- magma that reaches Earth’s surface• Lava flows happen with non-explosive eruptions
– Explosive• Shoots hot debris and gases• No lava flows, but massive debris• Dust clouds up the atmosphere
Explosive V. Non-Explosive
List a few characteristics of each type of explosion. Be prepared to share!
Cross Section of a Volcano
• Volcanoes form around vents that release magma
Magma!
• Explosive Magma!– High water content– High silica content• Creates an eruption with stiff
magma and releases gases
What Erupts?• Pyroclastic Material – – hot debris from the volcano
• Four types of Lava:1. Blocky Lava2. Pahoehoe3. Aa4. Pillow
1. Blocky Lava– Cool, stiff lava– Doesn’t travel far
2. Pahoehoe– Slow flowing lava– Like dripping wax– Forms glassy surface
3. Aa– Hawaiian for “Jagged
Lava”– Forms jagged– Underneath continues
to move
4. Pillow Lava– Forms underwater– Rounded, bubble
lumps
Types of Pyroclastic Material
1. Volcanic Blocks- Largest pieces- Solid Rock
2. Volcanic Bombs- Blobs of magma that harden in the air
3. Lapilli -Little stones -Pebbles
4. Volcanic Ash-gases expand rapidly and shoot hot ash
Which type of Pyroclastic material is most harmful to the environment? Why?
Assignment1. What are the four types of lava?2. What are the types of pyroclastic material?3. How is pyroclastic material categorized?4. Why do you think that volcanic eruptions
with water are explosive?5. Draw a non-explosive erupting volcano
including its vents.
What Causes Volcanoes
Chapter 9 Sec 3
Formation of Volcanoes
• Volcanoes are formed by the build up of cooled lava and other pyroclastic materials
• Magma is a mixture of liquid and solid rock material at high temperatures
• A large number of volcanoes lie on the plate boundaries
What are the three types of plate boundaries?Transform, Divergent, Convergent
• Boundaries– Volcanoes form at boundaries where tectonic action is
at– Ring of Fire!• Area of immense volcanic activity Surrounding the Pacific Plate
When Plate Separate• What boundary is associated with plate
separation?Divergent!
• Magma rises through the rift in the ocean floor forming new crust
• Produce what underwater sea features? Mid-Ocean Ridges
DID YOU KNOW…. Divergent boundaries can also be continental. It’s rare, but true!
When Plates Collide!• Which boundary is associated with plate
collision?Convergent!
• Common where oceanic subducts under continental crust
• Oceanic plate moves downward, melts in the mantle, forms magma
• Magma rises to the surface and forms volcano!• Why do oceanic plates always subduct beneath
continental?Oceanic is denser than continental!
Hot Spots• Hot Spots- weak areas of crust where magma
comes through – The Hawaiian islands are formed from volcanic
activity, but are no where near a plate boundary!
• Hot Spots often produce chains of volcanoes as the Hot Spot remains permanent and the plate moves over it.
• Is it possible to live on a previous hot spot?Yes! Hawaiians do so daily!
Predicting• Extinct- A volcano that hasn’t erupted in
recorded history• Dormant- A volcano that has not erupted in
some time• Active- have shown signs up erupting
• Before become active, what type of volcano was Dante’s Peak?
Dante’s Peak was dormant. Goes to show you, always proceed with caution!
• Signs of Eruption1. Eruptions are preceded by many small quakes2. The Volcano’s slop may bulge indicating a build up in
the magma chamber3. Increase levels of volcanic gases4. Infrared images from outer space show temperature
changesWhat two gases did Pierce Brosnan detect on Dante’s Peak?Sulfur Dioxide and Carbon Dioxide, both are common volcanic gases used for detection today
Assignment1. Please draw and label the convection currents of
the mantle.2. What are the four main predictions for volcanic
activity?3. Where are most divergent boundaries found?4. Why do oceanic crusts always subduct under
continental crust?5. How do Hot Spots leave a string of volcanoes?6. What is the difference between extinct and
dormant volcanoes?