By : Adriana,
A Volcano is …
Volcanoes are opening’s in the earth’s crust. When
the volcano erupts gas and rocks come out of the
opening. The rock is very hot so it is molten. There
are pockets of magma underneath the earth in
some parts of the world. The magma presses
against rock, the earth’s crust.When the magma
finds a spot in the crust where there aren’t very
many rocks, it pushes to the surface.
Types of Volcanoes
This is the simplest type of volcano.
It is built from particles and blobs of congealed lava ejected from a single vent
this volcano has a bowl- shaped crater.
They are steep – sided.
They have a crater at the summit which contains a central vent or clustered group of
Lava either flows through breaks in the wall or issue from fissures on the flanks of
This type of volcano is sometimes called strato volcanoes.
More Types of
It is built almost entirely of fluid lava flow.
Flow after flow pours out in all directions from a central summit vent
or group vents, building a broad gently sloping cone of flat, domical
shape, with a profile much like a shield.
Lava commonly erupt from rift zones that develop or flanks of the
Diameters of 3 or 4 miles.
There are heights of 1,500 or 2,000 feet .
The place where 2 tectonic plates collide is called a convergent boundary.
As the descending oceanic plate scrapes the continental plate, it sinks
deeper and deeper into the mantle, getting hotter. The combination of
increased heat and pressure causes the water in the oceanic crust to
be released . The water then mixes with the mantle rock causing it to
melt. On its way to the surface, heat from rising magma may cause
some of the overlying continental crust to melt and become part of the
magma. The silica from the continental crust then becomes part of a
gooey, silica rich lava that is likely to cause an explosive eruption
when it finally reaches the surface.
Crater Lake is the main feature of Crater Lake National Park. It fills
nearly a 4,000 feet deep caldera that was formed by the collapse of
the volcano, Mount Mazama. The lake is 5 by 6 miles with an
average depth of 1,148 feet. Its deepest point has been measured at
1,949 feet deep. As with any lake, its depth fluctuates with the
climate, particularly rainfall. This makes Crater Lake the deepest
lake in the U.S. Crater Lake also holds the honor of being the
deepest lake in the world. The caldera rim ranges in elevation from
7,000 to 8,000 feet. Crater Lake is known for its famous piece of
driftwood named the “Old Man of the Lake.” It is a full sized tree
that has been bobbing vertically in the lake for more than a
century. It contains one of the most cleanest water in the U.S.
Ring of Fire
The ring of fire is an arc of intense seismic earthquakes and volcanic
activity stretching from New Zealand along the eastern edge of Asia.
It is composed of over 75% of the world’s active and dormant
volcanoes. Three- fourths of earth’s active and dormant volcanoes lie
along this arc at the margin of the pacific ocean. The ring stretches
from South America, where the Nazca plate dips beneath the South
American plate, pushing up the Andes mountains and then north up
along the coasts of Central America and Mexico. Volcanoes form
where the magma breaks through the plates. In the Pacific Northwest
the tiny Juande Fuca plate is sinking beneath the North American
plate. As it dips beneath the North American plate and before it melts
completely, the two plates can snag and then break free. The result is
Mauna Loa is the largest volcano on our planet. It is the most active
volcano on earth. Located in Hawaii, it has been erupting for over
100,000 years. The volume of Mauna Loa is 9,600 cubic miles
(40,000 cubic kilometers) . It is 4 kilometers above sea level.
Mauna Loa means “long mountain.” It is a shield volcano and is
made of a rock -type known as tholeiitic basalt.
Types of Eruptions
There are more than 500 active volcanoes that have erupted at least
once with recorded history. Many volcanoes are in and around the
Mediterranean Sea. Mount Etna in Sicily is the largest and highest
of the mountains. Some volcanoes crown island areas lying near the
continents, and others form chains of island in the ocean. The most
spectacular eruptions consist of violent explosions that blast great
clouds of gas and debris. The type of volcanic eruption is often
labeled with the name of a well-known volcano where
characteristics behavior is similar.
Types of Lava
Blocky lava is cool, stiff lava that can not travel far from the erupting
vent. It usually oozes from a volcano only after an explosive eruption has
released much of the gas pressure from the magma chamber. Blocky lava
forms jumbled heaps of sharp edged chunks.
Pahoehoe lava flows slowly, forming a glassy surface with rounded
wrinkles. The lava gets its name from the Hawaiian word for ‘’ropy’’
because its surface represents coils of rope.
More Types of Lava
Aa is a hawaiian word that refers to a type of lava that has a jagged
surface. This slightly stiffer lava pours out quickly and forms a
brittle crust. The crust is torn into jagged pieces as the molten lava
underneath continues to move. Aa is named after the sound you
were to walk across this type of lava bare foot.
Pillow lava forms when lava erupts underwater. It forms rounded
lumps that are the size and shape of pillows. Pillow lava has a
rounded shape because contact with water causes rapid cooling of
the lava’s surface.
Mount St. Helens
Mt. St. Helens formed a conical, youthful volcano known as the Fuji
San at America. During the eruption, the upper 400 meters of the
summit was removed by the slope failure. Mt. St. Helens gets its
power from the heat deep inside the earth. In the months before the
eruption, the surge of molten rock or magma inside it triggered
earthquakes. The day it erupted was May 18, 1980. The eruption
generated a massive lateral blast that devastated the northern flank
of the volcano. It flattened millions of Douglas fir trees over a fan
shape of 600 square kilometers.
Mount St. Helens
This buried, burned, and crushed 51 people. The mountain top lost
1,300 feet of height. The valley of the North Toutle River filled
with 3 billion cubic yards of rock, ash, snow, and ice. About 230
square miles were severely damaged. Trees blew down 7 miles away.
Mt. St. Helens was known as one of the most pituresque
sratovolcanoes in the Cascade range. It caused 1.2 billion dollars in
damage. The real name of Mt. St. Helens is Mt. St. Hellacious.
Mt. Pelee Eruption
The volcano of Mt. Pelee looms over the village of St. Pierre on the
French Carribean Island of Martinque . In January 1902 Mt.
Pelee began to show an increase in fumarole activity. The public
showed a little concern. On April 23 minor explosions began at the
summit. Over the next few days, St.Pierre was showered in ash,
and covered with choking gas. An estimated 50 people, mostly
children, died by snake bites, along with 200 animals. At about
7:50 a.m., on May 8th , the volcano erupted. A large black cloud of
a super-heated gas, ash and rock rolled down the south flank of Mt.
Pelee at 100 mph. It struck St. Pierre in less than one minute with
hurricane force. Of the 28,000 people in St.Pierre, there were only
two known survivors.