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Volcanic
Eruptions
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How are Volcanoes Formed?Volcanoes are formed in various sizes and shapes. Cone-shaped volcanoes
are the most common ones. Some volcanoes are only a long crack in the earth's
crust. Volcanoes that resemble high mountains are the ones that are formed due to
many volcanic eruptions.
According to the theory of plate tectonics, the crust of the earth has many
rigid plates that are floating. It is the pressure created by the currents caused by the
heat energy from the earth's core that causes the movement of these plates. When
the pressure becomes intense, the plates either move towards each other or away
from each other horizontally.
When two plates collide, one of the plates goes beneath the other, causing a
friction in the earth's crust. The pressure caused by the friction will cause the
underlying rocks to melt and make the magma rise. The hot, orange-red lava is
thrown out of the mountaintop. Volcanoes of this type are considered threats to
living beings. Their eruptions are violent and cause destruction to all living things in
their proximity.
A gap is formed when two layers of plates move away from each other. The
hot lava rises through this gap. Volcanoes of this type occur on the ocean bed and
is not visible. However, if a volcano erupts violently from an ocean, it rises above the
ocean to create an island. Some volcanoes are formed in hotspot areas. The
hotspots are the center-points of the earth plates. These plates are connected to
the hot mantle of the earth. In brief, volcanoes are formed when the hot lava(magma) shoots out of the earth's crust. The lava becomes hard on cooling down to
form a volcanic mountain.
Causes of Volcanic Eruption
The buoyancy and pressure of the gas within the earth's crust cause a
volcano to erupt. Magma is formed when the upper mantle of the earth melts. A
volcano erupts when the magma (the hot liquid) rises upwards by the pressure ofgas that is dissolved in it. This is one of the three predominant theories.
According to the second theory, magma contains dissolved substances such
as water, sulfur dioxide and carbon dioxide. The solubility of the gases is high as the
pressure increases. The solubility of water decreases as the magma moves closer to
the earth's surface and eventually separates from the magma.When the ratio of the
gases becomes more in magma it causes the magma to disintegrate into
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pyroclasts, a combination of partially molten and solid fragments, and the volcano
erupts explosively.
The third theory says that a volcano erupts when new magma is injected into
a chamber that is already brimming with magma of similar or different compositions.
The eruption occurs when the magma moves upwards due to the additional push
exerted by the injection of new magma.
Positive and negative effects of an eruption
Positive Negative
The dramatic scenery created by volcanic
eruptions attracts tourists. This brings income to
an area.
Many lives can be lost as a result of a
volcanic eruption.
The lava and ash deposited during an
eruption breaks down to provide valuable
nutrients for the soil. This creates very fertile soilwhich is good for agriculture
If the ash and mud from a volcanic
eruption mix with rain water or melting
snow, fast moving mudflows are created.These flows are calledlahars.
The high level of heat and activity inside the
Earth, close to a volcano, can provide
opportunities for generating geothermal
energy.
Lava flows and lahars can destroy
settlements and clear areas of woodland
or agriculture.
Human and natural landscapes can be
destroyed and changed forever.
Mount Pinatubo is part of a chain of composite volcanoes along the Luzon arc onthe west coast of the island (area map). The arc of volcanoes is due to the
subduction of the Manila trench to the west. The volcano experienced major
eruptions approximately 500, 3000, and 5500 years ago. The events of the 1991
Mount Pinatubo eruption began in July 1990, when a magnitude 7.8 earthquake
occurred 100 kilometers (62 miles) northeast of the Pinatubo region, determined to
be a result of the reawakening of Mount Pinatubo. In mid-March 1991, villagers
around Mount Pinatubo began feeling earthquakes and vulcanologists began to
study the mountain. (Approximately 30,000 people lived on the flanks of the volcano
prior to the disaster.) On April 2, small explosions from vents dusted local villages with
ash. The first evacuations of 5,000 people were ordered later that month.
Earthquakes and explosions continued. On June 5, a Level 3 alert was issued for two
weeks due to the possibility of a major eruption. The extrusion of a lava dome on
June 7 led to the issuance of a Level 5 alert on June 9, indicating an eruption in
progress. An evacuation area 20 kilometers (12.4 miles) away from the volcano was
established and 25,000 people were evacuated.
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Wildfires
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Description:A is any uncontrolledfirein combustible vegetation that occurs in the
countryside or awildernessarea. Other names such as , ,
, , , , , , and may be
used to describe the same phenomenon depending on the type ofvegetationbeing
burned. A wildfire differs from other fires by its extensive size, the speed at which
it can spread out from its original source, its potential to change direction
unexpectedly, and its ability to jump gaps such as roads, rivers andfire breaks.
Wildfires are characterized in terms of the cause of ignition, their physical
properties such as speed ofpropagation, the combustible material present, and the
effect of weather on the fire.
Wildfires occur on every continent exceptAntarctica. Wildfires are a common
occurence inAustraliaespecially during the long hot summers usually experienced in
the southern regions such aVictoria, Australia. Due toAustralia'shot and dry
climate, wildfires (commonly refered to asbushfiresin Australia) pose a great risk
to life and infrastrucure during all times of the year, though mostly throughout the
hotter months of summer and spring.. In the United States, there are typically
between 60,000 and 80,000 wildfires that occur each year, burning 3 million to
10 million acres of land depending on the year. Fossil records and human history
contain accounts of wildfires, as wildfires can occur in periodic intervals Wildfires can
cause extensive damage, both to property and human life, but they also have various
beneficial effects on wilderness areas. Some plant species depend on the effects offire for growth and reproduction, although large wildfires may also have negative
ecological effects.
Strategies of wildfire prevention, detection, and suppression have varied over
the years, and international wildfire management experts encourage further
development of technology and research. One of the more controversial techniques
iscontrolled burning: permitting or even igniting smaller fires to minimize the
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amount of flammable material available for a potential wildfire. While some wildfires
burn in remote forested regions, they can cause extensive destruction of homes and
other property located in thewildland-urban interface: a zone of transition between
developed areas and undeveloped wilderness.
Wildfires are mainly caused due to climate change and human activities. Some of the
common causes of wildfires are:
Wildfires caused due to lightning occur at a frequency of three tofive per year. Since lightning is usually associated with rain, such wildfires do
not spread over large areas.
Majority of the cases of wildfires occur due to humancarelessness, especially while handling fireworks. Debris burning and arson
(burning to destroy property) are examples of other human activities that
often result in wildfires.
This common practice of farming refers to cuttingand burning of woodlands and vegetation for clearing the land. Quite often,
the slash-and-burn practice results in catastrophic wildfires.
Sometimes, volcanoes create a favorable condition forignition of wildfires in the nearby areas. Wildfires are also caused due topyroclastic clouds, generated from active volcanoes.
Very often, underground coal fires cause wildfires.Underground coal fires are the slow and flameless forms of combustion, below
the earth's surface. Such fires continue to burn for many years, resulting in
the release of toxic fumes and destruction of vegetation and human property.
Though, natural disaster and human activity cause wildfires, it is estimated that 90
percent cases of wildfires are due to human interaction with nature, either directlyor indirectly.
Wildfires are more prevalent in summer and autumn. They are also common during
droughts, when the fallen branches and leaves become dry and flammable. However,
the overall spread of wildfires depend on weather, type of vegetation and geography
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and topography of the area. Under the influence of strong winds, wildfires can
spread to more than 40 miles a day, which is about 1000 acres per hour.
In order to extinguish wildfires, firefighters use pulaski (combination of an ax and
hoe) to dig a fireline. While constructing a fireline, the mineral soil is exposed (byremoving the surface litter and organic matter), so as to stop the spread of
wildfires. In case of huge wildfires, helicopters and airplanes are used for spraying
water and fire-retardant chemicals to extinguish the fire.
The effects of wildfires are: People lose there homes, animals are killed and also lose
there vegetation, affects the air quality, the wind and heat. The good that wildfires
do is they burn old dead trees, leaves, grass, anything that mother nature has not
yet destroyed herself. Most fires leave a lot of animals homeless to say, which
causes them to come into the city's nearest the fire and create a lot of havoc in
the city around people.
Read
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Thousands of Californians have been told to flee the path of
intensewildfiresthreatening 12,000 homes in the Los Angeles area after two
firefighters were killed trying to tackle the blazes.
The state governor, Arnold Schwarzenegger, urged those in the fire's way to get out
as ash rained down on cars in downtown Los Angeles. The fires were spreading in all
directions in the dry conditions.
Firefighters fixed their attention yesterday on the blaze's fast-moving eastern side
where flames lapped at the foot of the vital communications and astronomy centre
of Mount Wilson, and on the north-western front, where the two firefighters were
killed on Mount Gleason, near the city of Acton.
"We ask for your understanding, for your patience as we move through this difficult
time, and please, prayers for the families of our two brothers that we lost," county
deputy fire chief Mike Bryant said through tears at a news conference.
Fire Captain Tedmund Hall, 47, and firefighter Specialist Arnaldo "Arnie" Quinones,
35, were killed in a crash, said Los Angeles county fire captain Mike Savage.
Authorities did not give a cause for the crash, and officials would take no questions
on the deaths.
Television helicopter video last night showed an upside-down vehicle on the
mountainside."Our hearts are heavy as we are tragically reminded of the sacrifices
our firefighters and their families make daily to keep us safe," Schwarzenegger said
in a statement.
The blaze was only about five per cent contained and had scorched 71 square
miles in the Angeles national forest. Mandatory evacuations were in effect for
neighbourhoods in Glendale, Pasadena and other cities and towns north of Los
Angeles. Officials said air quality in parts of the foothills bordered on hazardous. The
fire, which broke out Wednesday afternoon, was the largest of many burning
aroundCalifornia, including a new blaze in Placer county, north-east of Sacramento,
that destroyed 60 structures, many of them homes.
The southern California fire was expected to reach the top of Mount Wilson, where
22 television stations, many radio stations and cell phone providers have their
transmitters, said US forest service captain Mike Dietrich.
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Firefighters were pulled from the top of the mountain after clearing brush
and spraying retardant on antennas because it was too dangerous for them to
remain."We've done all the preparation we can," county fire spokesman Mark Savage
said.
Television stations said if the antennas burned broadcast signals would be affectedbut satellite and cable transmissions would not be.
Two giant telescopes and several multimillion-dollar university programmes are housed
in the century-old Mount Wilson observatory. The complex of buildings is both a
historic landmark and a thriving modern centre for astronomy.
At least 18 homes were destroyed in the fire and firefighters expected to find many
more, authorities said.
While thousands fled, two people who tried to ride out the firestorm in a backyard
hot tub were burned. The pair in Big Tujunga Canyon, on the south-western edge of
the fire, "completely underestimated the fire" and the hot tub provided "no
protection whatsoever", sheriff's spokesman Steve Whitmore said yesterday.
The pair made their way to firefighters and were airlifted out by a sheriff'srescue helicopter. Deputies gave them adequate notification to evacuate from
deputies but decided to stay, Whitmore said.
Whitmore described their condition as "critical" but fire officials said one of
the two was treated and released and the other remained hospitalised in stable
condition. A third person was burned on Saturday in an evacuation area along
highway two near Mount Wilson, officials said. Details of that injury were not
immediately known.
"There were people that did not listen, and there were three people that got
burned and got critically injured because they did not listen," Schwarzenegger said at
a news conference at the fire command post.