Transcript Volcanoes and Plate Tectonics

Volcanoes and Plate Tectonics
Volcano: a weak spot in the crust where
molten material or magma comes to the
surface
Magma: a molten mixture of rock-forming
substances, gases, and water from the
mantle
Lava: what magma is called when it
reaches the surface
Volcanoes at Plate Boundaries
• 600 active volcanoes on land
• Volcanic belts form along the plate boundaries
• One famous volcanic belt is the RING OF FIRE
Volcanoes occur at:
1. Divergent boundaries
2. Convergent boundaries
Island arc: string of islands created by erupting
volcanoes
Hot spot: area where material from deep within
the mantle rises and then melts
- Volcanoes form above hot spots
Mapping Earthquakes and Volcanoes
• Google Earth and Catastrophic Events World
map
• Latitude & Longitude locations given
Properties of Magma
Element: a substance that cannot be broken
down into other substances - examples:
Carbon (C), Hydrogen (H), Oxygen (O)
Compound: a substance made of two or more
elements that have been chemically combined
– examples: water (H2O), carbon dioxide (CO2)
Physical property: any characteristic of a substance
that can be observed or measured without
changing the composition of the substance.
Examples: density, hardness, melting point, smell,
freezing point
Chemical property: any property that produces a
change in the composition of matter.
- ability to combine or react with other substances
Examples: when burned: changes color, produces a
gas, forms new substance
Properties of Magma
Viscosity: the resistance of a liquid to flow
• High viscosity = slow moving = thick magma
• Low viscosity = fast moving = thin magma
• The viscosity of magma depends upon its
silica content and temperature
Silica: compound made of oxygen and silicon
• Silica content of magma = 50-70%
• more silica = higher viscosity, forms rhyolite
rock (similar to granite)
• less silica = lower viscosity, forms basalt rock
Types of lava
Pahoehoe: fast moving, hot lava that has a low
viscosity
- Looks like a whole bunch of wrinkles
Aa: slow moving, high viscosity lava
- Looks like large lava chunks puffed up
-
Which type am I?
Parts of a Volcano
Magma chamber: located underneath the volcano
where the magma collects
Pipe: a long tube in the ground that connects the magma
chamber to the earth’s surface
Vent: the opening in the volcano where molten gas and
rock are expelled
Lava flow: area covered by lava as it pours out of the
vent
Crater: bowl-shaped area that forms on top of the
volcano located around the central vent
*Tell students volcano diagram page #, quiz to follow on
Tuesday
• http://egsc.usgs.gov/isb/pubs/teacherspackets/volcanoes/poster/poster.html
• http://www.brainpop.com/science/earthsyste
m/volcanoes/
Types of Eruptions
Quiet Eruption: eruption where magma is
low in silica and has a low viscosity
- Lava flows quietly from the vent and can
flow for many kilometers
Shhhhh… the volcano
is erupting!
Explosive Eruption: eruption where magma
has a high silica content and viscosity
- Magma can flow out of the crater or build
up in the volcano’s pipe until it explodes
(think of cork getting stuck in a bottle)
- Produces bombs and cinders
Pyroclasic flow: mixture of hot gases, ash,
cinders, and bombs
Life Cycle of a Volcano
• Active: volcano that is erupting or has shown
signs that it may erupt in the near future
• Dormant: volcano that is expected to awaken
in the future and become active
• Extinct: volcano considered to be dead and is
unlikely to erupt again
Aerial view of volcano
Volcanic Landforms
Shield Volcanoes: quiet eruptions that gradually
build up a gently sloping mountain
Cinder Cone Volcanoes: explosive eruptions that
creates a cone-shaped hill from ashes, cinders
and bombs building up around the vent
Composite Volcanoes: cone shaped mountains
formed from layers of lava and ash from quiet
and explosive eruptions
Lava Plateaus: made up of many layers of thin
runny lava that erupt from long cracks in the
ground
Calderas: massive hole left by the collapse of a
volcano.
• Read page 102 to see how they form
Landforms from Magma
Volcanic Necks: forms when magma hardens in
a volcanoes neck – looks like a giant tooth
Batholiths: rock formed when a large body of
magma cools inside the crust
• Read pages 103 - 104
Geothermal Activity
Hot Springs: forms when groundwater is heated by
a nearby body of magma or by hot rock deep
underground
Geyers: fountain water and steam that erupts from
the ground
Geothermal Energy: using water heated by magma
to provide energy (pipes, turbine  generator)