VOLCANOES

1
VOLCANOES

• Lauren McCarthy

2
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
3
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.e
du/.../Mt.20Presley.htm
www.worldbook.com/.../studying_eruptions
www.Wikipedia.com
Kilauea volcano in Hawaii.
4
Types Continued

• 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.

St. Augustine volcano, Alaska.
The Novarupta Dome formed during the 1912
eruption of Katma Volcano, Alaska.
www.educ.uvic.ca/.../438/VOLCANO/COMPOSITE.html
http//pubs.usgs.gov/gip/volc/types.html
5
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, bowl-shaped crater. Sometimes these
  calderas fill with water, as happened at Crater
  Lake in Oregon.

http//www.livescience.com/environment/volcano_ove
rview.html http//www.pacificislandtravel.com/nat
ure_gallery/volcanoes1.gif http//youtube.com/wat
ch?vWv-LxFeQwPIfeaturerelated
6
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 apart-
• most 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_spotl
ight/volcanoes/where
7
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
8
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
9
Volcanoes in your backyard!