Unit 3 Assignment Gel111
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Unit 3 Assignment: Volcanoes
The ring of fire refers to the region that navigates around the Pacific Ocean where many
volcanoes and earthquakes frequently occur. The shape of the Ring of fire is more of a horseshoe
shape that is approximately 25,000 mile long. (Wikipedia Contributors). Its boundaries include
many tectonic plates such as the pacific plate, Juan de Fuca Plate, Cocos Plate, Indian- Australian
Plate, Nazca Plate and the Philippines Plate. (National Geographic). The Ring of fire includes the
entire Pacific coasts of North and South America and some islands in the western Pacific Ocean
including the entire Island countries of the Philippines, New Zealand and Japan. The Ring of fire
is where approximately 75% of all the volcanoes on the Earth are located and where 90% of the
Earth’s earthquakes occur with the majority of world’s strongest earthquakes occurring within
the Ring of Fire (The editors of Encyclopedia Britannica). This area is prone to many
earthquakes because there is a large amount of movement amongst the tectonic plates in this
region. This movement of these tectonic plates are causing subduction zones where the
volcanoes are formed and the earthquakes are occurring. Some of the most significant volcanic
eruptions that have taken place in this region would be the eruption of Mount saint Helens in
1980, Krakatoa in 1883, Mount Ruiz in 1985, and Mount Pinatubo in 1991. Some of the largest
earthquakes that have occurred in this region would be the Chile earthquake in 1960, the Japan
earthquake in 2011, and the earthquake in the Indian Ocean that was the producer of the deadly
tsunami in 2004 (The editor of Encyclopedia Britannica).
Mount Vesuvius is a stratovolcano that was formed because of the collision of two
tectonic plates, the African and the Eurasian plates (Wikipedia Contributors, “Mount Vesuvius”).
Stratovolcano can also be called a composite volcano and they are built up by many layers of
hardened lava. These volcanoes are typically found at subduction zones. This type of volcano has
a steep profile with a summit crater and periodic eruptions (Wikipedia Contributors,
“Stratovolcano”) Mount Vesuvius is unfortunately famously known for its eruption in AD 79 that
completely buried the nearby city of Pompeii.
When Mount Vesuvius erupted, it spewed a cloud
of super-heated tephra (rock fragments that are ejected from a volcano) and gasses, ejected often
rock, pulverized pumice and hot ash. This type of eruption has been dubbin a Vesuvian eruption
which is described as an eruption that has columns of hot gas and ash that are capable of
reaching the stratosphere (Eruption of Mount Vesuvius in 79 AD). Pompeii was completely
buried by 13-20 feet of ash that was spewed from Mount Vesuvius and freezing all life in
Pompeii at the moment of burial (Wikipedia Contributors, “Pompeii”). Buildings started to
collapse from the weight of the ash that was overloading the roofs trapping the people that were
still left in the city. If any of the trapped residents were still alive at this point, it was only for a
short amount of tie. The day after the eruption and the raining down of the choking ash, a
pyroclastic flow of hot gas and volcanic matter covered everything including Pompeii in its path.
Pompeii was then completely buried in millions of tons of volcanic ash, killing everting that was
let behind (history.com Editors).
There are four different types of volcanoes that have been identified by geologists. There
are cinder cones, composite volcanoes, shield volcanoes and lava domes. Cinder cones are the
smallest and simplest type of volcanoes. They are cone shaped hills that are made up of ejected
igneous rock known as cinders. Cinder volcanoes have a slope of 30 to 40 degrees and have a
bowl-shaped crater at the top (King). Composite volcanoes have been called grand and
picturesque with a concave shape that continues to get steeper as it nears the top. They are
symmetrical cones that have been built up by alternating glows of lava, volcanic ash, cinders and
blocks (Waston). Many of these volcanoes can reach upwards of 8,000 feet in height. Shield
volcanoes are named because they resemble a shield that is laying on the ground. They are
formed from the eruption of low viscosity lava that is able to travel further and flows thinner
than other lave. Lava usually erupts from the vents in the fractures that are developed on the
flanks of the cone. Lave domes form by viscous magma being erupted onto the surface and then
piling up around the vent, they usually do not have enough gas, or pressure to erupt explosively,
but they can sometimes be preceded or followed by explosive activity. The lava that forms the
domes is often too thick and sticky and does not flow very far, and instead piles thick and high
around vent.
There are two main types of lava, Mafic lava and Felsic lava. Mafic lava has a low
viscosity and flows very easily. Gases are able to escape this type of lava because it is very fluid.
When volcanoes erupt with Mafic lava, they flow instead of exploding from the volcanoes.
It is
formed in the oceanic crust and is high in magnesium and iron. Mafic lava is the lava that form
the Hawaiian Islands. Felsic lava is very viscous, very thick and does not flow very easily. It
contains a very high gas content which when pressure is release the high gas content of wear
vapor and carbon dioxide results in a violent explosion. Felsic lava is formed in the continental
crust and is high in silica content. On of the most common rocks formed from felsic lava would
be granite.
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