VOLCANOES
Lauren McCarthy
What is a Volcano?
• A volcano is an opening,
or rupture, in a planet's
surface or crust, which
allows hot, molten rock,
ash, and gases to
escape from below the
surface. Volcanic activity
involving the extrusion of
rock tends to form
mountains or features
like mountains over a
period of time.
The 25th Anniversary of Mt. St.
Helens Eruption.
http://en.wikipedia.org/wiki/Volcano pun.org/.../2005/05/25th-anniversar.html
What are the Types?
4 Main Types:
1. A shield volcano has shallow-sloping sides.
Shield volcanoes are formed by lava flows of low
viscosity — lava that flows easily. Consequently,
a volcanic mountain having a broad profile is
built up over time by a flow after flow of relatively
fluid basaltic lava issuing from vents or fissures
on the surface of the volcano.
Many of the largest volcanoes on Earth are
shield volcanoes (All of the volcanoes in Hawaii).
2. A cinder cone is a steep conical hill of
volcanic fragments that accumulate around and
downhill from a and is usually active in eruption
and is usually termed hot spot. The rock
fragments, often called cinders or scoria, are
glassy and contain numerous gas bubbles
"frozen" into place as magma exploded into the
air and then cooled quickly. Cinder cones range
in size from tens to hundreds of meters tall.
Mt. Presley located in New
Avalon
library.marist.edu/.../Mt.%20Presley.h
tm
www.worldbook.com/.../studying_eruptions
www.Wikipedia.com
Kilauea volcano in
Hawaii.
Types Continued…
St. Augustine volcano, Alaska.
The Novarupta Dome
formed during the 1912
eruption of Katma
Volcano, Alaska.
3. Composite volcanoes or stratovolcanoes are
typically steep-sided, symmetrical cones of large
dimension built of alternating layers of lava flows,
volcanic ash, cinders, blocks, and bombs and may
rise as much as 8,000 feet above their bases.
Some of the most conspicuous and beautiful
mountains in the world are composite volcanoes,
including Mount Fuji in Japan, Mount Cotopaxi in
Ecuador, Mount Shasta in California, Mount Hood
in Oregon, and Mount St. Helens and Mount
Rainier in Washington.
4. A lava dome or volcanic dome are formed by
relatively small, bulbous masses of lava too viscous
to flow any great distance; consequently, on
extrusion, the lava piles over and around its vent. A
dome grows largely by expansion from within. As it
grows its outer surface cools and hardens, then
shatters, spilling loose fragments down its sides.
www.educ.uvic.ca/.../438/VOLCANO/COMPOSITE.html
http://pubs.usgs.gov/gip/volc/types.html
How do they Work?
Volcanoes form when chambers
of magma, or hot molten rock,
boil to the surface. These
magma chambers often remain
sealed for hundreds of years
between eruptions, until the
pressure builds sufficiently to
break through a vent, which is a
crack or weak spot in the rock
above.
The blast creates a crater,
where lava and ash spill out,
forming the cone. On some
volcanoes, the magma chamber
collapses after a violent
eruption and a caldera forms,
which is just a large, bowlshaped crater. Sometimes
these calderas fill with water, as
happened at Crater Lake in
Oregon.
http://www.livescience.com/environment/volcano_overview.html
http://www.pacificislandtravel.com/nature_gallery/volcanoes1.gif
http://youtube.com/watch?v=Wv-LxFeQwPI&feature=related
Where and How do they form?
Most volcanoes are found along a belt, called the Ring of Fire, that encircles the
Pacific Ocean. Volcanic activity also occurs in such places as Hawaii, Iceland,
southern Europe, and at the bottom of the sea.
Plate tectonics is the main reason for the formation of volcanoes..
Volcanoes can form when:
Two plates collide- One of the plates is then forced under the other. As the plate sinks,
friction and Earth's heat cause part of it to melt. This melted part then rises as
magma. When it reaches the surface, it produces a volcano.
Two plates spread apartmost such movement takes place on the ocean floor. As the plates move apart,
magma below the crust moves up between the plates. Large amounts of lava pour
onto the surface and build up the ocean floor. Magma sometimes creates an
underwater mountain range, such as the huge Mid-Atlantic Ridge that runs down the
length of the Atlantic Ocean.
Magma Theory- Some scientists believe such volcanoes develop when a huge column
of magma rises from inside Earth toward the surface. It comes close enough to the
surface that it sometimes breaks through and forms a volcano. A number of
volcanoes, for example those in Hawaii lie far from the plate boundaries. And this is
where this theory come in.
http://www.worldbook.com/wb/Students?content_spotlight/volcanoes/where
Creation of Landforms
There are four main land forms that can occur due to volcanoes:
1. Lava flows- is a (moving) outpouring of lava, which is created during a non-explosive
effusive eruption; which forms igneous rock when it cools.
2. Volcanic Peaks- A volcanic peak is what we tend to think of when we talk about
volcanoes. It is a volcano that has formed a large cone shaped hill, or mountain.
These cones typically have a large bowl shaped crater in the top center.
3. Caldera- Calderas are massive crater-like depressions that can cover many tens of
square miles. These calderas form when volcanoes explode with terrible
destruction, completely obliterating the original volcano, and surrounding area.
4. Volcanic Neck- A volcanic neck is the remnant of an old volcano. As the volcano
died, the last bit of lava inside of the volcanoes opening, or neck, cooled and
hardened. Over many hundreds of thousands of years the material around the
neck is removed by erosion, leaving only the harder neck behind.
www.kidsgeo.com/.../0054-volcanoes-landforms.php
Lava flow: Located in Hawaii
Spewing lava 10 miles high.
A Volcanic peak (located above)
And a Volcanic neck (below).
A Caldera: Crater Lake
www.kidsgeo.com/.../0054-volcanoes landforms.php
Volcanoes in your backyard!