1. Volcanoes and Eruptions
8SCIENCE
Date
Title
Page
16/04/13
Volcanoes and Eruptions

2. Review Where do volcanoes form? How do volcanoes form?
Plate boundaries
How do volcanoes form?
Heat and pressure from inside the Earth produces magma and pushes up to the surface
What is a hotspot?
Very hot areas in the mantle that produce volcanoes although they are not found on plate boundaries

3. Identify the cause of each volcano below using the words: subduction, rift, and hot spot.
a) In 1973, a town in Iceland called Vestmannaeujar was surprised when lava began erupting from a vent or crack in the Earth’s surface. The Earth’s crust seemed to split apart._______________________
b) Scientists feel that the Cascade Mountains, extending from California to British Columbia, are still forming. Two plates are colliding, forcing magma up from the mantle to form the mountain. _____________________
c) Mauna Loa in Hawaii is the “growing mountain”. In 1969 and 1974, it erupted and poured out lava through a hole in the Earth. This lava called and hardened into rock. Below it, molten lava continues to flow. _____________________

4. Types of Volcanoes
Shield
Cinder cone
Composite

5. Introduction to the three types of volcanoes
As you view the video clip, try to think of some of the similarities and differences between the three types of volcanoes.

6. Shield volcanoes
Quiet eruption that produces lava and spreads out in flat layers
These layers build to form slightly sloping sides
Ex: Hawaiian islands produces 2 different types of lava:
Pahoehoe (smooth)
- A’a (rough and chunky)

7. Pahoehoe and A’a lava
A’a lava
Pahoehoe

8. Cinder cone volcano
Explosive eruptions that throw lava and rocks high into the air
These bits of rock and hardened lava are called tephra
Tephra layers build up to form steep sided volcanoes

9. Tephra lava
Tephra lava erupted from the 1980 Mount St. Helens Eruption in Washington State

10. Composite volcano Produces eruptions that are quiet then violent
Cycles of lava and tephra form different layers
Usually found where one plate is forced under another(subduction zone)

11. Let’s review with animations…
Types of Volcanoes

12. What causes an eruption to be quiet or violent?
Amount of water vapor and other gases trapped in magma
High gas content = more violent eruption
Gases are trapped in magma and pressure builds up
As magma moves closer to the surface, there is less pressure and the gas can escape
Amount of silica (silicon and oxygen) present in magma
Low in silica = more quiet eruption

13. Other volcanic structures
Not all magma flows to the surface
Some may rise from the volcano and cools underground to form other rock structures
Erosion of the rock layers make these visible to us today

14. CALDERAS IN OREGON (US) AND PHILLIPINES
DEATH VALLEY, CALIFORNIA
SHIPROCK, NEW MEXICO
COLOMBIA