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Volcanowatch

March 27, 2003

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


April is tsunami awareness month throughout Hawai`i

Strand line of tsunami wave at Halape, Hawai`i overturned boat in Hilo, Hawaii
November 29, 1975 tsunami damages. Left: Submerged coconut grove at Halape. This part of the coast subsided by as much as 3.5 m, leaving the grove submerged in 1.2 m of water. The tsunami swept over the area in foreground, reaching 13.1 m above the shoreline. The highest wave reached 14.6 m above the postsubmergence shoreline. | med | large | Right: The tsunami overturns a boat at the Wailoa River small-boat harbor in Hilo, Hawai`i. | med | large |

About this time every year, we have an article or two on the topic of tsunami. The month of April is observed as "Tsunami Awareness Month" in Hawai`i. It is important that everyone living in Hawai`i learn about tsunami because more people have been killed by tsunami than by any other natural hazard in Hawai`i.

It is easy to be unaware about tsunami because the last fatal one occurred in 1975, and the last statewide event was in 1960. A large portion of the population was too young or not in Hawai`i to remember these events. This article is for them. Those residents who have experienced the devastating effects of a tsunami will always remember it.

On April 1, 1946, a tsunami, generated by a magnitude-7.8 earthquake in the Aleutian trench, struck the Hawaiian Islands and caused 159 fatalities. On April 2, 1868, an earthquake beneath the southeast flank of Mauna Loa with an estimated magnitude of 7.9 produced waves that swept coastal villages from Ka Lae to Kumukahi. This locally generated tsunami killed 75 residents.

These two events represent the types of tsunami that can affect Hawai`i - those that are spawned by large earthquakes in the subduction zones around the Pacific Rim and those that are from large local earthquakes. For us, the practical difference between these two types is the time it takes the waves to reach Hawai`i after the earthquake.

A personal experience shared by a recent visitor to HVO highlights this difference and points out how a little knowledge can be dangerous. The visitor from Waimea and his wife had lived aboard a boat in the Ala Wai harbor for about 30 years and had gone through a number of tsunami warnings. All of these warnings were from tsunami originating from Pacific Rim earthquakes and allowed them several hours to evacuate.

However, while visiting Kailua-Kona and staying in a ground floor room at an ocean-side hotel on November 29, 1975, they were told by hotel personnel to immediately move up to a higher floor in the hotel because a tsunami was coming. This tsunami was from the magnitude-7.2 Kalapana earthquake, and it took only 27 minutes to reach Kailua-Kona. The visitor and his wife, thinking that they had hours to move up to a higher location, barely were able to make it out of their room after the first wave came crashing in. His wife had fallen in the water, and they had to scramble for their lives.

Locally generated tsunamis are very dangerous because they can strike so quickly and without a tsunami warning from Civil Defense. If you are near the ocean when a large earthquake occurs, move immediately to higher ground. Don't wait for a tsunami-warning siren to sound; let the violent shaking be your alarm.

Since 1837, 33 tsunami, at least four of which were locally generated, have struck Hawai`i with varying severity. It would be worth your while to take the time and look at the yellow-edged pages in the front section of your telephone directory. Disaster preparedness information and tsunami evacuation maps can be found there.

Public education is one way that we can mitigate this hazard. The mission of the Pacific Tsunami Museum in Hilo is to promote public tsunami education for the people of Hawai`i and the Pacific region. They believe that through education and awareness, no one should ever again die in Hawai`i due to a tsunami.

We have a long way to go to convince the public of this deadly hazard. During the last statewide tsunami warning, O`ahu Civil Defense authorities counted over 400 surfers waiting in the water for the waves to arrive. Fortunately, a large tsunami did not materialize, or we would have had 400 more fatalities.

The Hawai`i State Civil Defense has arranged a series of events to promote tsunami awareness in April. On April 1, State CD will be testing their statewide warning and communications system. Throughout the month they will provide tsunami resources for media briefings. Three tsunami-related productions will be shown at multiple times on cable television's "Kid Science" program. On the Big Island, "Kid Science" can be seen on cable Channel 53. The informative presentations are "Science of Tsunamis," Tsunami Warnings and Evacuation," and "Surviving Tsunamis," a video about locally generated tsunamis in Hawai`i. Check your TV program listings for the date and time of the shows.

Although we promote tsunami awareness in April, people should be conscious of the hazard throughout the year. Just as it doesn't rain in Hilo only in April, earthquakes and tsunami can occur at any time of the year.

Activity Update

Eruptive activity at the Pu`u `O`o vent of Kilauea Volcano continued unabated during the past week. Scattered surface breakouts from the western "Kohola" lobe of the Mother's Day flow are seen throughout the inflating flow. Another finger of lava from the eastern side of the Kohola flow is approaching the sea cliff above the Wilipe`a delta. The two surface flows on Pulama pali from breakouts of the main Mother's Day tube system are crusting over but are still visible after dark. The steam plume at the West Highcastle delta has enlarged, and the volume of lava entering the ocean has probably increased.

The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The steam clouds are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary and onto the lava deltas and benches.

One earthquake was reported felt during the past week. Two residents of Leilani Estates subdivision felt an earthquake at 5:27 p.m. on March 20. The magnitude-2.3 event was located 1 km (0.6 mi) west of Pu`ulena Crater at a depth of 2 km (1.2 mi).

Mauna Loa is not erupting. The summit region continues to inflate, but seismic activity remains low, with only three earthquakes located in the summit area during the last seven days. skip past bottom navigational bar


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Updated: March 31, 2003 (pnf)