Volcanoes erupt when pressure from gases and magma built up in the volcano's magma chamber is too great. This is similar to the pressure build up in a balloon until it bursts. When the pressure is released, gases and molten rock (magma) are ejected from the volcano in explosive eruptions or flow out as lava in nonexplosive eruptions. Volcanoes form at boundaries where tectonic plates meet, especially at subduction zones, as well as at hot spots in the mantle.

1. Why Does a Volcano Erupt?
• What would happen if you
were to stick a pin into a
balloon? (it would burst)
• Why does it explode?
• Pressure inside the balloon is
suddenly released and the
gases escapes rapidly.
• This is what happens in a
volcano.

2. Volcanoes Vents
form around Lava
vents that
release magma
onto the Earth’s
surface.
Magma chamber

3. Types of Volcanic Eruptions
1. Nonexplosive Eruptions have lava flow.
1. Explosive Eruptions have lava fountains.
•What is Lava?
magma that flows onto
the Earth’s surface
•What is magma?
Liquid rock from the
mantle

4. What Erupts from a
Blocky lava
Volcano?
Lava can be
thick or thin.
Pahoehoe
Aa
Pillow lava

5. What Erupts from a Volcano?
Pyroclastic material:
• Rock fragments created by eruptions
•magma explodes from volcano and solidifies in the air
•existing rock is shattered by powerful eruptions
Lapilli
Volcanic bombs
Volcanic blocks
Volcanic ash

6. How do volcanoes affect the Earth?
Flows and Fallouts
• hot ash can flow really quickly
•Knock down buildings
•Dam rivers (flooding/drought)
•Kill crops and livestock
Climatic Changes
•Ash & Gases can block sunlight
•Drop average global temperature
noticeably

7. Types of Volcanoes
1. Shield volcano
2. Cinder cone volcano
3. Composite (Stratavolcano) volcano

8. Where do volcanoes occur?
•Divergent Plate Boundaries
•Subduction Zones

9. What causes volcanoes?
The Formation of Magma
• Mantle rock melts when the
temperature increases
or the pressure decreases.

10. Where do Volcanoes Form?
•Tectonic Plate Boundaries
~75% world’s active volcanoes in Ring of Fire

12. What Causes Volcanoes?
•Hot Spots: areas of persistent volcanic activity
•Originate at unusually hot areas of the mantle-
core boundary.
•Plumes of magma rise and poke through the
crust forming volcanoes

13. How do volcanologists predict
eruptions?
• Measuring Small Quakes
– Before eruption, increase in number & intensity
• Measuring Slope
– Bulges may form with magma (tiltmeter)
• Measuring Volcanic Gases
– Outflow of volcanic gases
• Sulfur dioxide, carbon dioxide
• Measuring Temperature from Orbit
– Measure changes in temperature over time

14. You should not be a • You don’t like
Volcanologist if…. hiking,
backbacking,
rockclimbing, etc.
• You are not
interested in
experiencing
extreme
temperatures and
heights.
• If you don’t like to
travel to incredible
places and see
breathtaking views
of the world.