1. Volcanic Eruptions 3.3 Objectives:
Explain what happens when a volcano erupts.
Describe 2 types of volcanic eruptions
Identify stages of volcanic activity

2. Volcanic Eruptions 3.3 What comes out of volcanic explosions?
Ash, lava, steam, rock, gases, dirt
Magma forms in the asthenosphere
Convection currents in the mantle bring magma towards the surface
Magma tries to flow into any open crack
When magma reaches a weak spot in the crust, a volcano forms
Lava is magma that has reached the surface

3. Magma Reaches Earth’s Surface
Volcanoes are systems of passage ways through which magma moves.
Inside a Volcano
Magma collects below the volcano in the magma chamber
Magma flows upward through a tube (pipe) that connects the magma chamber to the surface.

4. Magma Reaches Earth’s Surface
Inside a Volcano
Gas and magma leave through vents
Central vent is the opening at the top
Side vent anywhere along the side of the volcano
Lava pours out of the vents and creates a lava flow
A bowl shaped area called a crater may form around the central vent

5. Crater
Vent
Pipe
Side Vent
Lava Flow
Magma Chamber

6. Magma Reaches Earth’s Surface
A Volcanic Eruption
Dissolved gases are trapped
in magma under extreme
pressure (CO2 in a soda bottle)
as magma flows , pressure because there is less rock on top of it.
the dissolved gases expand and form bubbles
When a volcano erupts, the force of the expanding gas forces magma up the pipe until it explodes out the vent

7. Content checkpoint… think/pair share…take two minutes to answer these questions with a partner nearby…..
What common everyday occurrence can we relate to a volcanic eruption?
What happens to the pressure in the magma as it rises toward the surface?

8. Kinds of Volcanic Eruptions
Volcanic eruptions can be quiet or explosive.
Eruptions depend on the properties of magma
Silica content
Viscosity

9. Kinds of Volcanic Eruptions
Quiet Eruptions
Magma has low silica content = low viscosity
Magma flows easier so gases bubble out gently
Lava can flow many kilometers from the vent
Produce both pahoehoe and aa lava
Example: Hawaiian Islands – Mount Kilauea

10. Kinds of Volcanic Eruptions
Explosive Eruptions
Magma has high silica content = high viscosity
Magma doesn’t always flow out of vent and so it builds up (like a cork in a bottle)
Trapped gases build up pressure until they explode
Magma is pushed out of the vent with incredible force

11. Kinds of Volcanic Eruptions
Explosive Eruptions
Lava breaks into fragments that cool quickly and harden into different sizes
Ash – fine, dust sized particles of lava
Cinders – pebble sized particles
Bombs – baseball to car sized chunks of lava
Pyroclastic flow: when an explosive eruption hurls out gases, ash, cinders and bombs.
Pumice forms when lava cools quick and traps air bubbles inside
Obsidian forms when lava cools quick leaving the surface smooth and glass-like

12. Kinds of Volcanic Eruptions
Volcano Hazards
Quiet eruptions cause lava to flow far --- burning and burying everything in its path
Explosive eruptions can bury entire towns in ash, cause landslides, avalanches, cause damage from gases and cinders/bombs.

13. Content checkpoint… think-pair-share take two minutes to answer these questions with a partner nearby.
What is pyroclastic flow?
How does volcanic ash cause damage?
What is the main difference between a quiet eruption and an explosive eruption?

16. Stages of Volcanic Activity
Life Cycle of a Volcano
Scientists use historical records and monitor volcanoes to determine what stage of activity a volcano is in
A volcano can be active, dormant or extinct
An active volcano is erupting or showing signs of near future eruptions
A dormant (sleeping) volcano can awaken in the future and become active
An extinct (dead) volcano is unlikely to erupt ever again

17. Stages of Volcanic Activity
Monitoring Volcanoes
Geologists use tiltmeters to detect slight changes in surface elevation cause by magma moving underground
They monitor gases escaping from a volcano
Increase in temperature might mean magma is nearing the surface
The changes detected may give a short warning time BUT
We cannot be certain the type of eruption or how powerful it will be

18. Think and Discuss….
Which is more likely to be dangerous – a volcano that erupts frequently or a volcano that has been inactive for a hundred years? WHY?