Download Chapter 12 PowerPoint

yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project

Document related concepts
Extrusive Igneous Formations
• Openings in the Earth that erupt gases,
ash, & lava.
• Lava flows destroy everything in their
• Pyroclastic flows (ash & debris) rush
down the sides of the volcano.
• Acid rain is produced when sulfurous
gases mix with water vapor in the
Parts of a Volcano
–Magma collects in a magma chamber
inside the Earth’s crust.
–The opening where magma is forced
up and flows onto the Earth’s surface
is called a vent.
–The steep-walled depression around
a volcano’s vent is called the crater.
Magma Chamber
Formation of Volcanoes
–Form at Divergent & Convergent
plate boundaries.
–Hot Spots :
»An unusually hot area between
the mantle & core that forces
melted rock upward to form
volcanoes in the middle of
tectonic plates.
»Plate moves as the hot spot is
Hawaiian Islands
Ring of Fire
3. Volcanic Eruptions
• The explosiveness of a volcano depends on:
» Amount of water vapor & other gases
trapped in the magma.
» Amount of silica present in the magma.
- Basaltic lava is low in silica & produces
quiet, non-explosive eruptions:
•Pāhoehoe (meaning "smooth,
unbroken lava” =smooth, billowy,
undulating, or ropy surface)
•A’a (meaning "stony rough
lava” = rough or rubbly surface
composed of broken lava blocks)
Pāhoehoe lava flowing over a’a
Pāhoehoe lava flowing over a’a
- Granitic & andesitic
magma are high to
intermediate in silica &
produce violent eruptions.
pyroclastic flow
Types of Volcanoes
» Broad volcanoes with gently sloping
» Quiet eruptions of basaltic lava forming
flat layers.
Cinder Cone
»Steep-sided volcanoes made of loosely
packed tephra.
»Tephra- bits of rock or solidified lava
(pyroclastic material) like ash, cinders,
bombs, & blocks.
• Volcanoes with alternating layers of tephra
& lava flows.
• Long dormancy periods
• Violent eruptions
• Also known as a stratovolcano
Mount St. Helens
Mount St. Helens after May 1980 eruption.
Intrusive Igneous Formations
• Largest intrusive formations
• Forms where magma has been forced
up into chambers within the crust &
cool slowly.
• Magma that is forced into vertical
cracks that cuts across rock layers and
• Magma that has been forced into cracks
that are parallel to rock layers and then
Volcanic Necks
• The solid igneous rock core of an
extinct volcano.
• Weathering & erosion wear away the
cone exposing the neck.
• Large depression caused by the
collapse of a crater during an eruption.