Transcript Mountains and Volcanoes

December 18, 2012
Q-2 Pg.
Daily Goal: We will explain why volcanoes
erupt and how volcanoes are different from
mountains.
Homework: Revise your test!
Science Starter:
1. How are island chains formed?
2. List one positive and one negative effect of
volcanoes.
Mountains and Volcanoes
What’s the difference?
•
Mountains
Remember when we made mountains with graham
crackers?
• Which type of boundary made mountains?
Mt. Everest is the tallest mountain
(above water) in the world.
• Mt. Everest was once
the floor of a shallow
sea. If you were to climb
Mt. Everest, you would
be standing on rocks
containing the remains
of ocean animals.
• How can rocks from the
sea floor be on top of a
mountain on a
continent?
Mountain ranges happen at
convergent plate boundaries.
• When two plate boundaries collide, the plates
push together. Plates can be oceanic or
continental. The land has nowhere to go but up.
Volcanoes can also happen at plate
boundaries.
• A volcano is an opening in Earth’s crust which
molten rock, rock fragments and gasses
escape.
How Magma Forms at a Divergent
Boundary •Mantle material rises
to fill the space opened
by separating tectonic
plates. As the pressure
decreases, the mantle
begins to melt and rise
up.
•Because magma is less
dense than the
surrounding rock, it
rises toward the
surface, where it forms
new crust on the ocean
floor.
How Magma Forms at a Convergent
Boundary
•As the oceanic plate
moves downward,
some of the rock
melts and forms
magma.
•When magma is less
dense than the
surrounding rock, it
rises towards the
surface.
Mountains don’t erupt. Volcanoes do.
Why?
• The mantle holds a lot of gasses.
• Remember what happens when gas gets hot?
– Does it spread out (become less dense) or pack
together (become denser)?
• Do less dense things rise or sink?
***Write this down!***
• When the gas rises, it pushes against the
crust, and creates a lot of pressure. This
pressure creates cracks. The cracks open
up space for the magma to get through.
In your notebook,
• Explain what we did for the demo.
• Explain how the demo is like a volcano.
– Be sure to include the words: pressure, gas,
expand, dense, erupt
• Draw a diagram of the demo.
– Label what is happening. (Include the direction.)
• Draw a diagram of a volcano.
– Label what is happening. (Include the direction.)
Ring of
What is the ring of fire?
Write down what you think the
3 key points
are from the text we just read.