Natural disasters in Hawaii

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.