Hilo Bay Tsunami

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29 April 2011
The Hilo Bay: Tsunami Magnet of Hawaii
On the afternoon of 22 May 1960 the Valdivia Earthquake struck the country of Chile with devastating repercussions for the Chilean people and people around the world. The Earthquake rated a 9.5 on the moment magnitude scale and is, to date, the most powerful earthquake ever recorded. It occurred at roughly 1911 GMT, 1411 local time, and generated a massive tsunami that struck Hawaii approximately fifteen hours later. The tsunami caused little damage to the Hawaiian Islands in general, except in the case of one particular town on the coast of Hilo Bay, on the main island of Hawaii. The tsunami’s power at Hilo Bay was magnified many times compared to its effects throughout the rest of Hawaii. This magnification effect was due to the unique location and topographical features of the bay, which caused the tsunami surges to increase in size and strength by an order of magnitude. In addition to the increase in tsunami size and power, insufficient public education and awareness also contributed to the scope of the disaster. In the end the waves caused nearly $75 million in damage and claimed 61 lives.

In order to understand the disaster at Hilo Bay, it is prudent to examine some of the information about the Great Chilean Earthquake that caused it. The Valdivia Earthquake was the largest ever recorded and caused incredible damage in the cities of Temuco and Valdivia. Over 1,655 people were killed, 3,000 were injured, and nearly 2,000,000 people found themselves homeless. The quake also caused some $550 million dollars in damage (adjusted for inflation, that’s nearly $3 billion 2011 dollars!) (Wikipedia). The main quake caused significant damage due to the obvious trembling and shaking expected in such a massive earthquake, but even more damage was caused by the tsunami that was generated. The massive wave quickly destroyed coastal towns, liquefied the soil, polluted local water sources due to massive erosion and debris (including whole houses) washed into the area’s rivers and streams. Even though the damage and death toll were extensive, many experts believe the catastrophe could have been much worse if the Chilean people had not been accustomed to geologic disturbances leading them to build their homes and businesses with earthquake safety in mind (U.S.G.S.). Earthquake-proofed structures and countermeasures no doubt saved countless lives.

The quake was caused by a megathrust event on the Nazca Plate and the South American Plate on the Peru-Chile Trench. This area is a subduction zone, where the Nazca Plate is being forced under the South American Plate. These types of plate boundaries are responsible for the highest energy release possible for the world’s earthquakes. In fact, all of the earthquakes measuring magnitude 9.0 and above were megathrust earthquakes. No other earthquake classification is known to be able to produce earthquakes of this size. The rupture zone for the Great Chilean Earthquake was estimated to be about 1000 km long, from Lebu to Puerto Aisen. In addition, 1 to 1.5 m of subsidence occurred along the Chilean coast from the south end of the Arauco Peninsula to Quellon on Chiloe Island, and as much as 3 m of uplift occurred on nearby Isla Guafo (Wikipedia). This incredible, destructive force immediately created huge tsunami that caused massive damage in Chile before propagating throughout the ocean and destroying towns and businesses throughout the Pacific region.

The tsunami spawned in Chile struck all along the coasts of South America with incredible force and wave heights of up to 11.5 m, quickly eclipsing the damage and deaths caused by the earthquake originally, while the main wave began a deadly journey across the Pacific Ocean. The tsunami not only caused damages and deaths in Hawaii and Chile, but also in Japan and the Philippines. The waves were powerful enough to cause a 5.5 m tsunami to hit Honshu, Japan a full day after the...
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