Natural disaster
A natural disaster is the effect of a natural hazard (e.g. flood,
tornado , volcano eruption, earthquake, or landslide) that
affects the environment, and leads to financial, environmental
and/or human losses. The resulting loss depends on the
capacity of the population to support or resist the disaster, and
their resilience. This understanding is concentrated in the
formulation: "disasters occur when hazards meet vulnerability."
A natural hazard will hence never result in a natural disaster in
areas without vulnerability, e.g. strong earthquakes in
uninhabited areas. The term natural has consequently been
disputed because the events simply are not hazards or disasters
without human involvement.
Tornadoes
Different Types of Tornadoes
Supercell Tornadoes
Some of the most violent tornadoes develop from supercell
thunderstorms. A supercell thunderstorm is a long-lived thunderstorm
possessing within its structure a continuously rotating updraft of air.
These storms have the greatest tendency to produce tornadoes, some of
the huge wedge shape. The supercell thunderstorm has a low-hanging,
rotating layer of cloud known as a “wall cloud.” It looks somewhat like
a layer of a layer cake that hangs below the broader cloud base. One side
of the wall cloud is often rain-free, while the other is neighbored by
dense shafts of rain. The rotating updraft of the supercell is seen on radar
as a “mesocyclone.”
The tornadoes that accompany supercell thunderstorms are more likely
to remain in contact with the ground for long periods of time—an hour
or more—than other tornadoes, and are more likely to be violent, with
winds exceeding 200 mph.
Landspout
Generally weaker than a supercell tornado, a landspout is not associated
with a wall cloud or mesocyclone. It may be observed beneath
cumulonimbus or towering cumulus clouds and is the land equivalent of
a waterspout. It often forms along the leading edge of rain-cooled
downdraft air emanating from a thunderstorm, known as a “gust front.”
Gustnado
Weak and usually short-lived, a gustnado forms along the gust front of a
thunderstorm, appearing as a temporary dust whirl or debris cloud.
There may be no apparent connection to or circulation in the cloud aloft.
These appear like dust devils.
Waterspout
A waterspout is a tornado over water. A few form from supercell
thunderstorms, but many form from weak thunderstorms or rapidly
growing cumulus clouds. Waterspouts are usually less intense and
causes far less damage. Rarely more than fifty yards wide, it forms over
warm tropical ocean waters, although its funnel is made of freshwater
droplets condensed from water vapor from condensation - not saltwater
from the ocean. Waterspouts usually dissipate upon reaching land.
Dust Devils
Dry, hot, clear days on the desert or over dry land can bring about dust
devils. Generally forming in the hot sun during the late morning or early
afternoon hours, these mostly harmless whirlwinds are triggered by light
desert breezes that create a swirling plume of dust with speeds rarely
over 70 mph. These differ from tornadoes in that they are not associated
with a thunderstorm (or any cloud), and are usually weaker than the
weakest tornado.
Typically, the life cycle of a dust devil is a few minutes or less, although
they can last much longer. Although usually harmless, they have been
known to cause minor damage. They can blow vehicles off the road and
could damage your eyes by blowing dust into them.
Earthquakes
An Earthquake is a sudden shake of the Earth's crust.The vibrations may
vary in magnitude. The earthquake has point of origin underground
called the "focus". The point directly above the focus on the surface is
called the"epicentre". Earthquakes by themselves rarely kill people or
wildlife. It is usually the secondary events that they trigger, such as
building collapse, fires, tsunamis (seismic sea waves) and volcanoes,
that are actually the human disaster. As many of these could be avoided
by better construction, safety systems, early warning and evacuation
planning, the term unnatural disaster is not unwarranted.
Earthquakes are caused by the discharge of accumulated along geologic
faults.
Main article: List of earthquakes
Some of the most significant earthquakes in recent times include:
The 2004 Indian Ocean earthquake, the second largest
earthquake in recorded history, registering a moment magnitude
of 9.3. The huge tsunamis triggered by this earthquake cost the
lives of at least 229,000 people.
The 7.6-7.7 2005 Kashmir earthquake, which cost 79,000 lives in
Pakistan.
The 7.7 magnitude July 2006 Java earthquake, which also
triggered tsunamis.
Volcanic eruptions
Types of volcanic eruptions
An Eruption may in itself be a disaster due to the explosion of the
volcano or the fall of rock but there are several effects that may
happen after an eruption that are also hazardous to human life.
Lava may be produced during the eruption of a volcano a material
consisting of superheated rock. There are several different forms
which may be either crumbly or gluey. Leaving the volcano this
destroys any buildings and plants it encounters.
Volcanic ash - generally meaning the cooled ash - may form a
cloud, and settle thickly in nearby locations. When mixed with
water this forms a concrete like material. In sufficient quantity ash
may cause roofs to collapse under its weight but even small
quantities will cause ill health if inhaled. Since the ash has the
consistency of ground glass it causes abrasion damage to moving
parts such as engines.
Supervolcanos : According to the Toba catastrophe theory 70 to
75 thousand years ago a super volcanic event at Lake Toba
reduced the human population to 10,000 or even 1,000 breeding
pairs creating a bottleneck in human evolution. It also killed three
quarters of all plant life in the northern hemisphere. The main
danger from a supervolcano is the immense cloud of ash which
has a disastrous global effect on climate and temperature for
many years.
Pyroclastic flows consist of a cloud of hot volcanic ash which
builds up in the air above under its own weight and streams very
rapidly from the mountain burning anything in its path. It is
believed that Pompeii was destroyed by a pyroclastic flow.
Floods
Some of the most notable floods include:
The Huang He (Yellow River) in China floods particularly often. The
Great Flood of 1931 caused between 800,000 and 4,000,000
deaths.
The Great Flood of 1993 was one of the most costly floods in
United States history.
The 1998 Yangtze River Floods, also in China, left 14 million
people homeless.
The 2000 Mozambique flood covered much of the country for
three weeks, resulting in thousands of deaths, and leaving the
country devastated for years afterward.
Tsunamis
