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Hawaii is truly a paradise. However, the islands are
vulnerable to certain kinds of natural disasters, such as
flooding, hurricanes, tsunamis and life-threatening lava
flows.
In March 2006, more than 30 days of torrential rain resulted
in major damage from flooding, as well as serious public
health issues. The following are some of the natural disasters
that either have occurred or could occur in Hawaii.
 Flash
Floods
When there is heavy rain, some parts of each of the Hawaiian
Islands are susceptible to flash floods. Heavy rain can
turn a small, quiet river into a cascading one that sweeps
everything away that comes into its way. Every few years,
even lives are lost in flash floods, mostly people swept
away in their cars or hikers. An approaching heavy rain
can be difficult to forecast and may come suddenly.
In Hawaii, flash floods are much more common than other
natural disasters, such as tsunamis or hurricanes. It’s
not too long ago that serious flash floods hit the islands.
In October 2004, a flash flood occurred in Manoa Valley
on Oahu and completely soaked the ground floor of the University
of Hawaii at Manoa Hamilton library. Besides destroying
parts of the library, the flood trashed at least 60 homes
and caused more than $1 million dollars in damage.
In March 2006, a six-week rain period caused flooding in
many places in Hawaii. On Kauai, it caused a dam break killing
seven people. On Oahu, the rain caused Waikiki’s sewer system
to overflow, resulting in a sewage spill that polluted parts
of the island’s south shore for several days.
Hurricanes
Storm surge is a phenomenon caused by the extremely low
pressure and strong winds around the eye of a hurricane
or typhoon that cause a dome of water to form at levels
higher than the surrounding ocean surface. Large swells,
high surf and wind-driven waves ride atop this dome as it
impacts land areas causing extensive damage to facilities
and the shoreline environment.
This build-up of water can produce severe flooding in coastal
areas, particularly when storm surge coincides with normal
high tides. Any land mass in the path of storm surge will
be affected to a greater or lesser extent, depending upon
a number of factors. The stronger the storm and the shallower
the offshore waters, the higher the storm surge.
Storm surge is the most deadly of a hurricane's associated
hazards. A powerful tropical cyclone is usually described
in terms of its wind speeds, but coastal flooding causes
many more deaths than high wind.
Boats ripped from their moorings, utility poles and other
debris atop hurricane surge often demolish buildings not
destroyed by hurricane-force winds. Even without the weight
of debris, water is a powerfully destructive force.
Two hurricanes (Iwa and Iniki) left devastation and death
in their wake after passing through the state. Hurricane
Iwa hit the islands of Niihau, Kauai and Oahu on November
23, 1982. It was a Category 1 hurricane on the Saffir-Simpson
Hurricane Scale. Iwa was the first major hurricane to hit
Hawaii since statehood in 1959. Hurricane Iniki was the
most powerful hurricane to strike Hawaii in recorded history.
The eye of the hurricane passed over the island of Kauai
on September 11, 1992 as a Category 4 hurricane causing
six deaths and around $1.8 billion in damage.
 Tsunamis
Hawaii is the U.S. state at greatest risk for a tsunami.
Hawaii records about one a year, with a damaging tsunami
happening about every seven years. Early in the morning
on April 1, 1946, an earthquake with a reported magnitude
of 7.8 occurred in the Aleutian Islands off Alaska.
Almost five hours later, at 7 a.m., the largest and most
destructive tsunami waves in reported history struck Hawaii,
killing 159 people. Many were curious people, including
school children, who ventured into the exposed reef area,
not knowing the receding water to be a sign of an approaching
tsunami. No warning was possible nor given for this tsunami.
Property damage totaled approximately $26 million. Maximum
run-ups were reported to be 54 feet (16.5 m) on Molokai
and 55 feet (16.8 m) in Pololu Valley on the Big Island.
Waves in some areas penetrated more than half a mile inland.
Tsunamis are primarily associated with earthquakes in oceanic
and coastal regions. When an earthquake occurs, the energy
generated travels outward in all directions from the source.
Detecting tsunamis is challenging.
Tsunamis are generated by earthquakes and travel at varying
speeds. The fastest ones can reach 400-500 mph (645-805
kmh). In the open ocean, a tsunami is only about one foot
high, so that it would pass a ship unnoticed. Once it hits
shallow water, it slows down and builds up to a high, abrupt
front. Tsunamis hit the land as a series of coastal waves
and the largest wave is usually somewhere in the middle
of the set.
Tsunamis are characterized as shallow-water waves. Shallow-water
waves are different from the wind-generated waves many of
us have observed from the beach. Tsunamis in deep water
can have a wavelength greater than 300 miles (482 km) and
a period of about an hour.
This is significantly different from the normal California
tube, which generally has a wavelength of about 330 feet
(100.5 m) and a period of about 10 seconds. When a tsunami
reaches the shore, it may appear as a rapidly rising or
falling tide, or a series of breaking waves.
Reefs, bays, entrances to rivers, undersea features and
the slope of the beach all help to modify the tsunami as
it approaches the shore. Tsunamis rarely become towering,
breaking waves. Sometimes the tsunami may break far offshore.
On occasion, a tsunami may form a bore, a step-like wave
with a steep, breaking front, which can happen if the tsunami
moves from deep water into a shallow bay or river. The first
wave may not be the largest in the series of waves.
One coastal area may see no damaging wave activity, while
in another area, destructive waves can be large and violent.
The flooding of an area can extend inland by 1,000 feet
(305 m) or more, covering expanses of land with water and
debris. Flooding tsunami waves tend to carry loose objects
and people out to sea when they retreat.
Volcanoes
There are several kinds of events caused by volcanic
activity that can be harmful to life and property. These
include lava flows, lahars, ash falls, debris avalanches
and pyroclastic density currents.
Molten rock, or magma, that pours onto the Earth’s surface
is called lava. The higher a lava’s silica content, the
more viscous it becomes. Low-silica basalt lava can form
fast-moving, 10-30 miles per hour (16-48 kmh), narrow lava
streams or spread out into broad sheets up to several miles
wide.
Between 1983 and 1993, basalt lava flows erupted at Kilauea
Volcano on the Big Island of Hawaii, destroying nearly 200
houses and severing the coast highway along the volcano’s
south flank. Major hazards of lava flows include burying,
crushing, covering and burning everything in their path.
Lava flows can dam rivers to form lakes that might overflow
or break their dams causing floods. Methods for controlling
the paths of lava flows include constructing barriers and
diversion channels, cooling the advancing front with water,
or disrupting the of source or advancing front of the lava
flow by explosives.
Volcanoes emit gases during eruptions. Even when a volcano
is not erupting, cracks in the ground allow gases to vent
to the surface. The most common volcanic gases are water
vapor (90 percent), carbon dioxide, sulfur dioxide, hydrogen
sulfide and hydrogen.
Sulfur dioxide gas can react downwind with water droplets
in the atmosphere and fall as acid rain, causing corrosion
and adversely affecting vegetation. Carbon dioxide is heavier
than air and tends to collect in depressions, where on occasion,
it can accumulate in lethal concentrations and cause people
and animals to suffocate.
Large eruptions inject sulfur dioxide gas into the stratosphere,
where it combines with water to form an aerosol of sulfuric
acid. By reflecting sunlight, the sulfur aerosols can lower
the Earth’s average surface temperature by a few degrees
Fahrenheit. These aerosols also hasten ozone destruction
by altering chlorine and nitrogen chemical species in the
stratosphere.
 Earthquakes
Earthquakes in Hawaii are closely linked to the islands’
volcanoes. Even though hardly noticeable, thousands of earthquakes
happen every year beneath the Big Island of Hawaii. The
Big Island is the youngest of the Hawaiian Islands and is
still growing today. Here, flowing erupting volcanoes and
flowing lava can be witnessed. The island’s active volcanoes
are Kilauea, Mauna Loa and Loihi. Eruptions and magma movements
within these volcanoes are usually accompanied by frequent
small earthquakes. There earthquakes, also called volcanic
earthquakes, originate in regions of magma storage or along
paths that magma follows as it rises and moves before eruption.
Other earthquakes that can occur in Hawaii are called tectonic
earthquakes, which can happen in areas of structural weakness
at the base of the Hawaii’s volcanoes or deep within the
Earth’s crust beneath the island. In the last 150 years,
a few strong tectonic earthquakes (magnitude 6 to 8) caused
major damage to buildings and roads and even triggered local
tsunami. The most destructive earthquake in Hawaii occurred
on April 2, 1868, which killed 81 people. The earthquake
had a magnitude of 7.9, destroyed more than a hundred homes
and generated a 15 m high tsunami along Kilauea’s south
coast.
Even though earthquakes happen often in Hawaii, the majority
of them are too small to be felt. The last one that happened
on the Big Island of Hawaii that could be felt even
on the island on Oahu, 170 miles (274 km) to the north of
the epicenter, occurred on October 15, 2006. It had a magnitude
of 6.7. The earthquake caused property damage, injuries,
landslides, widespread power outages and airport delays
and closures. The most severe damage occurred on the north
and western sides of the Big Island of Hawaii. Damage was
also quite heavy on the eastern side of Maui and minor damage
spread all the way out to western Oahu.
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