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- [Narrator] On average, wildfires burn
up to five million acres of land
in the United States each year.
While they can start naturally, wildfires are often
caused by humans with devastating consequences.
Wildfires are large, uncontrolled infernos
that burn and quickly spread through wild landscapes.
Types of wildfires may include forest, brush,
and peatland fires, depending on the landscapes affected.
Wildfires require three components,
known as the fire triangle.
A heat source, fuel, and oxygen.
Heat sources, such as the sun, a hot bolt of lightning,
or a smoldering match can supply enough heat
to spark a fire.
That spark then turns into flames when fuel
or any flammable material is present.
Dry, dead grasses, leaves, and trees
are common fuels for wildfires,
but so are living vegetation, called green fuels.
Pine trees and other evergreens contain
flammable oils that can burn when exposed to a heat source.
As the fuel burns, the resulting flames feed
and thrive off of oxygen.
When air movement or wind occurs, not only is more oxygen
supplied to the fire, but it may also help transport
and spread the flames.
Since wildfires occur outdoors, they have a nearly
endless supply of oxygen from our atmosphere to burn.
Many wildfires are the result of natural causes.
A warmer climate and weather patterns like El Nino
can create the hot, dry conditions necessary
for fires to erupt.
However, about 90% of wildfires are caused
by human activity, such as campfires that become
uncontrollable, improperly handled cigarettes, or arson.
Although wildfires occur worldwide, they are most common
in the Western United States.
There, high temperatures, drought,
and frequent lightning and thunderstorms can create
the perfect setting for wildfires.
While they can be destructive, and sometimes even deadly
for humans, wildfires do play an important role in nature.
They can help a forest by removing harmful insects
or diseased plants and they can clear thick canopies
to help sunshine reach seedlings on a forest floor.
By being aware of the conditions necessary
for wildfires to occur, they can be managed and prevented,
thereby saving lives and making way
for the positive effects of wildfires.
(gentle music)


燃え上がる山火事、止まらない炎 (Wildfires 101 | National Geographic)

157 タグ追加 保存
Amy.Lin 2019 年 8 月 28 日 に公開
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