Tsunamis
[Illustration: Tsunami]
Tsunamis have killed more people in the Hawaiian Islands than all other natural disasters combined. The Hawaiian Islands have been hit by numerous tsunamis, some generated thousands of miles away, others the result of earthquakes and landslides occurring within the archipelago.
Given the numerous tsunamis in historic times, it is quite certain that the ancient Hawaiian were also familiar with this global ocean phenomenon. An ancient Hawaiian proverb states, “Kaha aku la ka nalu o ku‘u ‘āina.” (“The surf of my land has swept everything away,” and this is said to be “...a retort to one who boasts about the value and beauty of his own land.”[i]
Tsunamis are caused by earthquakes, landslides and volcanic eruptions. Potentially (and possibly historically) tsunamis may also be caused by meteor impacts. The word tsunami comes from the Japanese language, in which tsu means “harbor,” and nami means “wave.”
Summary of Major Tsunamis
That Have Hit the
Year: 1837.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake:
Year: 1868.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake: Hawai‘i
Year: 1877.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake:
Year: 1923.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake:
Year: 1923.
Deaths in
Islands Affected: O‘ahu;
Origin of Earthquake:
Year: 1933.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake:
Year: 1946.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake:
Year: 1951.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake: Hawai‘i
Year: 1952.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake:
Year: 1957.
Deaths in
Islands Affected: Kaua‘i; O‘ahu.
Origin of Earthquake:
Year: 1960.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake:
Year: 1964.
Deaths in
Islands Affected:
Origin of Earthquake:
Year: 1975.
Deaths in
Islands Affected: Hawai‘i
Origin of Earthquake: Hawai‘i
Major Tsunamis That Have Hit the
1837, Nov. 7—Kahului,
Minutes later a tsunami arrives. People, livestock, canoes, and the village’s 26 grass houses are all swept inland and deposited in a small lake. In Hilo, 100 houses are destroyed. In all, at least 15 people in the
1868, April 2—Hawai‘i Island: An earthquake measuring 8.0 on the Richter scale on the island of Hawai‘i causes a landslide that destroys a village and creates a localized tsunami reported to be more than 60 feet (18.3 m) high.
Nearly every European-style home in the Ka‘ū district of Hawai‘i
The mud flow buries a village of 31 people along with about 50 animals, killing 40 people in all. The tsunami kills 48 people when water surges ashore up to 60 feet (18 m) high, sweeping away the ancient village of ‘Āpua in Puna.
1877, May 9—Hawai‘i Island: A large earthquake occurs near Peru, and a tsunami arrives in Hilo before dawn. 37 houses are destroyed, 45 people are killed, and many more injured.
1901—Kailua-Kona: An 8.0 earthquake on the Tonga Trench generates a 4-foot (1.2-m) high tsunami that hits Kailua-Kona, causing minor damage.
1918—
1923, February 23—Big Island, Maui: An earthquake in the Aleutian Islands generates a tsunami that sends waves to more than 20 feet (6 m) above normal in the Waiākea area of Hilo, also causing serious damage in Kahului, Maui.
1946, April 1—Hawai‘i Island, Kaua‘i, Maui, O‘ahu: An earthquake in the Aleutian Islands generates a tsunami that hits the island of Hawai‘i, killing an estimated 159 people in the Hawaiian Islands, including 96 in Hilo and 24 in Laupāhoehoe on Hawai‘i Island.
The tsunami brings 15 waves in all (the third is the biggest), rising up to 56 feet (17 m) above sea level in some places, and 33 feet (10 m) in Hilo where close to 500 homes and businesses are destroyed and more than 1,000 more damaged, causing an estimated $26 million in damage, including railroads, bridges, piers and ships.
The 1946 tsunami also hits other Hawaiian Islands, killing 17 people on Kaua‘i, 13 on Maui, and six on O‘ahu, including one at Makapu‘u, two at Kahuku, and three at Kahana.
1957, March 9—Kaua‘i: An earthquake in the Aleutian Islands generates a tsunami that destroys 75 homes on Kaua‘i’s north shore.
1960, May 22—Hawai‘i Island: Sixty-one people in
About 15 hours later, on the morning of May 23,
122 are killed in
1964—Maui; Hawai‘i Island: One of North America’s largest earthquakes ever recorded (magnitude 8.4 on the Richter scale) occurs in Alaska, sending tsunami waves toward the Hawaiian Islands.
The tsunamis cause flooding in Kahului, Maui, where the waves rise to more than 11 feet (3.4 m) and in
1975, November 29—Hawai‘i
Two strong earthquakes shake the southeast region of Hawai‘i
The tsunami comes ashore near the site of an old Hawaiian village that is now a campground area called Halapē. The ground in the area sinks some 12 feet (3.7 m) and rocks fall from the cliffs above.
A tsunami wave sweeps campers onto a rugged lava field and washes some of them into a huge crack in the lava, killing two people and injuring many more. This tsunami also causes damage in
Anatomy of a Tsunami—Period, Wavelength, Speed
The time it takes one complete wave to pass a given point is known as the wave’s period. A typical tsunami may have a period from 9 to 30 minutes (e.g., the 1946 tsunami had a 15-minute period).
A typical tsunami has a wavelength of 50 to 300 miles (80 to 480 km), with some wavelengths exceeding 465 miles (750 km). A tsunami may travel across the ocean at about 475 mi/hr (764 km/hr).
The deeper the ocean, the faster the tsunami travels. For example, in water 20,000 feet (6,100 m) deep a tsunami travels in excess of 540 miles per hour (870 km/hr), but if the water is only 3,000 feet (915 m) deep, the tsunami travels less than 350 miles per hour (563 km/hr).
The Pacific Ocean is on average about 12,000 feet (3,658 m) deep, making it the deepest of the world’s oceans. Because of this extreme depth, Pacific Ocean tsunamis travel particularly fast.
When traveling across the open ocean, a tsunami is typically only several feet high. This low wave height is due to the fact that a tsunami’s wavelength reaches all the way to the seafloor, which may be more than 20,000 feet (6,100 m) from the ocean’s surface. The small surface height of a tsunami on the open ocean makes tsunamis hard to predict. Often the full terror of a tsunami becomes apparent only when the wave finally reaches shallow waters.
When a Tsunami Arrives
As a tsunami wave reaches land, the front of the wave moves slower in the shallower water. The back of the wave, still up to 100 miles (160 km) out to sea where it is much deeper, continues to move at hundreds of miles per hour while the front of the wave may slow to 30 mi/hr (48 km/hr).
When there is unequal speed between the back and front of the tsunami (or any wave), it causes the wave’s water to pile up upon itself. The result is that the tsunami grows in height, and may rise from 10 to 30 feet (3 to 9 m) or more. The extremely long wavelength of a tsunami may also cause a tremendous surge of water onshore, and may send water up to ½-mile (.8 km) inland.
When a tsunami nears shore, the trough of the wave arrives first, and may drain out a bay before the surge arrives about five to ten minutes later. Once a tsunami collides with a shoreline, it may then bounce (reflect back into the open ocean. The oscillations of a major tsunami may ripple back and forth across the whole Pacific Ocean for several days.
Each tsunami has unique characteristics depending upon its wavelength and direction, as well as how the tsunami was generated (e.g., landslide, earthquake, etc.) among other factors. Two other factors important in determining how severely a tsunami will affect any particular stretch of coastline are the angle at which the tsunami approaches the coast and the seafloor and bay configurations of the coastline area.
The 1946 tsunami hit Kaua‘i like huge breaking surf, but the 1957 tsunami arrived on Kaua‘i more like a massive flood tide, causing the sea to rise up to 32 feet (9.8 m) above normal.
The 1946 Tsunami
The 1946 tsunami that inundated part of the city of Hilo on Hawai‘i Island, was similar to one that hit Lisbon in 1775. During both tsunamis people drowned because they were curious at the sight of an empty bay and went out to look around, only to have the tsunami waves arrive a few minutes later to sweep them away.
The 1946 tsunami was caused by an earthquake in the
The first wave was said to resemble an extra high tide surrounding homes and buildings. The third and fourth waves were the biggest of some 15 tsunami waves, each arriving about 15 minutes after the previous one, with some of the waves reaching heights up to 56 feet (17 m) above sea level, killing people and destroying property. The natural shape of Hilo Bay amplified the waves, which then surged onto land.
As each wave receded it revealed the floor of Hilo Bay. Then the tremendous surge of water would arrive again, sweeping inland and destroying everything in its path. Ninety-six people in Hilo were killed by the waves. Nearly 500 homes and businesses were destroyed and more than 1,000 more damaged along with railroads, bridges, piers and ships, totaling an estimated $26 million of damage.
Other coastal areas on the island of Hawai‘i were also affected, including Laupāhoehoe where 24 people were killed. The 1946 tsunami also hit other Hawaiian Islands, killing 17 people on Kaua‘i, 13 on Maui, and six on O‘ahu (one at Makapu‘u, two at Kahuku, and three at Kahana).
1957 Tsunami
Certain bay shapes (e.g., Hilo Bay) tend to increase the size of tsunami waves approaching from particular directions. When Hawai‘i
The greatest wave heights occurred in small open bays with underwater topographies that had an amplifying effect on the wave’s size as it approaches shore.
The 1957 tsunami destroyed or severely damaged more than 75 homes along Kaua‘i’s north shore, including 25 of the 29 homes in the area called Hā‘ena. At O‘ahu’s Pōka‘ī Bay, more than 50 boats and six yachts were smashed against the breakwater.
An ancient Hawaiian proverb states, “Mimiki ke kai, ahuwale ka papa leho.” (“When the sea draws out in the tidal wave, the rocks where the cowries hide are exposed,” meaning, “secrets will out on the day of wrath.”)[ii]
[Photograph: 1957 tsunami]
The 1960 Tsunami
The last major Pacific-wide tsunami to hit the Hawaiian Islands was on May 22, 1960, and was caused by an earthquake in Chile. The Chilean earthquake occurred 6,600 miles (10,622 km) away from the Hawaiian Islands, moving a piece of land the size of California about 30 feet (9 m) in just minutes. The tsunami waves generated by the earthquake took more than 15 hours to reach Hawai‘i’s shores.
Hilo once again took the brunt of the damage as it was hit by at least seven significant tsunami waves over a 2-hour period. The third wave was the most destructive.
In
In all, 61 people were killed in Hilo, with 43 more requiring medical care for their injuries. In addition, at least 229 homes were destroyed, as well as 308 public structures and businesses. The destruction was most severe near Hilo’s Kamehameha Ave., where entire city blocks were washed away. Damage was estimated up to $50 million.
Many people died because they went to the shoreline to investigate what was happening as the water drained out from the bay and river. In all, the Chilean earthquake and the resulting tsunami caused the death of an estimated 2,000 people, mostly in Chile, but also 122 in Japan.
Localized Tsunamis
1868—Ka‘ū District, Hawai‘i Island
In 1868, an earthquake estimated to have a magnitude of 7.9 on the Richter scale struck the south end of the island of Hawai‘i. The quake caused a giant mudslide that killed hundreds of people and buried a small village, destroying nearly every European-style home in the Ka‘ū district.
The 1868 earthquake also generated what is known as a localized tsunami. Water reportedly surged ashore high enough to cover the tops of coconut trees, at least 60 feet (18.3 m) high at some spots along the Ka‘ū coast. The ancient village of ‘Āpua in Puna on Hawai‘i Island is swept away. The localized tsunami killed 48 people.
1975—Halapē, Hawai‘i Island
On the morning of November 29, 1975, two strong earthquakes shook the southeastern coastal area of the island of Hawai‘i. One of these earthquakes registered a magnitude of at least a 7.2 on the Richter scale.
The epicenter of the earthquake was located near an old Hawaiian village site called Halapē. The ground in the area sunk some 12 feet (3.7 m) and rocks fell from the cliffs above.
The earthquakes caused a small eruption of Kīlauea Volcano and generated a localized tsunami. When the tsunami came ashore at Halapē, it swept some Boy Scouts and their leaders (who were camping there) up onto a rugged lava field, and many were washed into a huge crack in the lava.
Nineteen people were injured, many severely, and two were killed, including a scout leader and a local fisherman. A huge piece of land actually slid into the ocean and the tops of the palm trees were sticking up from the water. One of the tsunami waves traveled more than 300 feet (91 m) inland.
Ancient Landslides and Tsunamis
Until recently many scientists accepted one researcher’s assertion that a giant landslide about 105,000 years ago had generated a tsunami that sent a wave as high as 1,000 feet (305 m) up the slopes of Lāna‘i. This theory has recently been largely discredited, though it may have occurred on a smaller scale.
It is likely, however, that about 1½ million years ago a massive landslide occurred on O‘ahu. Researchers believe this ancient landslide on O‘ahu involved nearly one-fourth of the island and sent a 100-mile (161-km) long piece of coastline on the Ko‘olau’s up to 50 miles (80 km) out to sea.
The landslide involved an estimated 25% of the
Another landslide-generated tsunami is believed to have sent a wave over the “saddle,” the relatively narrow strip of land connecting east and west
The next potential great landslide area is believed to be on Hawai‘i Island’s still-active Kīlauea Volcano where the entire south flank is moving about 4 inches (10 cm) per year—an average of about 3-1/3 feet (1 meter) every ten years—along the Hilina fault system. The moving piece of the volcano extends an estimated 5 miles (8 km) deep and covers an estimated 72 square miles (186 sq. km).
An increased rate of slippage occurred in November 2000 when it the flank moved about 3½ inches (9 cm) in just 36 hours, which is more than 200 times the normal speed. Satellite-based Global Positioning System (GPS) equipment installed from 1995 to 1999 allowed precise detection of the rapid flank movement.
No earthquake was associated with the increased rate of movement, which may instead have been related to heavy rains that had fallen five to ten days earlier. About 3 feet (.9 m) of rain had fallen on the south side of Kīlauea Volcano over a period of several days. Though this type of movement is not associated with an earthquake, it is often referred to as a “silent earthquake.”
Researchers theorize that the water may act as a lubricant along the fault line, also adding weight to the massive piece of Earth. Water pressure may also act like a wedge to pry open the fault system, which may have been the same system that caused the 1975 localized tsunami that killed two people at Halapē.
A large earthquake that occurred in the region in the 1860s may also have been due to a movement of this flank area directly south of Kīlauea Volcano’s caldera.
Worldwide—Other Historic Tsunamis
In 1883, more than 36,000 people were killed near Java and Sumatra when an explosion of Krakatoa Volcano created waves more than 100 feet (30 m) high. More than 22,000 people were killed in 1896 by an earthquake that hit Japan, creating a tsunami that also caused great damage in California, the Hawaiian Islands, and Chile.
The March 2, 1933 tsunami that was generated off Japan caused damage on the island of Hawai‘i and also destroyed 2,800 homes in Japan, killing 1,600 people. Worldwide, one of the biggest tsunamis on record occurred in 1958 when a landslide in a small Alaskan bay sent a wave surging 1,740 feet (530 m) above sea level on the opposite shoreline.
The Alaskan earthquake of 1964 created a tsunami that killed 107 people in
On September 1, 1992 an earthquake offshore of Nicaragua moved 170 miles (274 km) of seafloor and drained a 20-foot (6-m) deep harbor before the tsunami waves crashed ashore—170 people died and 13,000 were left homeless. In December, 1992 a tsunami killed more than 1,000 Indonesians.
One of the largest tsunamis ever to hit Japan occurred in July, 1993, when an earthquake occurred in the Sea of Japan. Waves from the tsunami inundated areas up to 97 feet (29.6 m) above sea level, resulting in 120 deaths.
A 7.7 earthquake in Java, Indonesia in 1994 created a tsunami that killed more than 200 people and sank 278 boats. More than 2,200 people died on July 17, 1998 when a wall of water up to 40 feet (12 m) high hit Papua New Guinea with little warning.
In the last century before 2004, there were more than 82 tsunamis worldwide, killing more than 70,000 people, and ten major tsunamis in the
On
One factor that has led to an increase in tsunami deaths is the increase of populations in coastal areas.
Tsunami Warning Systems
The Pacific Tsunami Warning Center at ‘Ewa Beach in O‘ahu is run by the National Oceanic and Atmospheric Administration (NOAA), and can detect an earthquake anywhere in the Pacific Ocean. The Center uses computers to determine the strength of the quake, and to determine the likelihood that a tsunami is generated.
There are more than 100 tide gauges in the Pacific Ocean that report to satellites, and these tide gauges can generally reveal if a tsunami is coming toward the Hawaiian Islands. The exceptions, however, are tsunamis arriving from north of the Hawaiian Islands, where there is no land (or tide gauges) for thousands of miles.
Tsunamis generated in the Aleutian Islands and heading toward the Hawaiian Islands have historically been difficult to positively detect. For example, warning sirens in the
Coastal areas of the
A tsunami warning in
New tsunami warning devices are now overcoming the technological difficulties and providing reliable early warnings.
Ocean Floor Sensors
New technological advances are improving the ability of scientists to determine if a tsunami has been generated. This improved technology helps to avoid false alarms and allows advance warnings to be given as early as possible. The new detection tools include deep ocean sensors with seafloor pressure gauges, broadband seismic sensors, buoys, and hydrophone arrays.
In 2001, scientists began installing a new tsunami detection system utilizing ocean floor sensors throughout the
One device was placed off the
As detection improves, officials will be better able to alert the public, helping to avoid loss of life from future tsunamis.
In 2006, the National Oceanic and Atmospheric Administration (NOAA) placed three new buoys off the coast of
Each Deep-Ocean Assessment and Reporting of Tsunami (DART) buoy is secured with a 3.4 ton (3 mtons) anchor, and the bottom pressure recorder is secured by a 720-pound (327-kg) anchor. The pressure recorder is comprised of a computer, a pressure sensor, and glass floats that are able to sense pressure changes caused by a tsunami as small as .4 inches (1 cm).
An acoustic modem transducer enables the data to be sent to a communication buoy at the surface (which also has weather instruments), and then the information is sent via radio waves to a GOES satellite, which relays it to a ground station where computers calculate the origin point of the tsunami, the tsunami’s speed, and when it will arrive at particular locations. Warnings are then sent to places that are in danger.
The
[Photograph: Tsunami]
[i]p. 140, Pukui, Mary Kawena. ‘Ōlelo No‘eau: Hawaiian Proverbs & Poetical Sayings.
[ii]p. 235, Pukui, Mary Kawena. ‘Ōlelo No‘eau: Hawaiian Proverbs & Poetical Sayings.
