April 2014: Commemorating –­ and monitoring – tsunamis

April is Tsunami Awareness Month in the State of Hawaii. As in previous years, groups across the state are conducting exercises and other activities to increase awareness of, and preparedness for, tsunami hazards.

On April 1 at the Wailoa Park memorial to the Shinmachi community that was devastated by the May 1960 tsunami, a service was held in memory of tsunami casualties. April 1 also marked the 68th anniversary of the 1946 tsunami that struck Laupahoehoe and claimed 159 lives in Hawaii.

Near the close of the service, the Civil Defense warning sirens were sounded as part of their monthly test. That morning, the sirens also provided those who attended a moment to pause and reflect.

After the ceremony, people returned to their weekday routines. Just two hours after the siren test however, an ominous alert flashed at the Pacific Tsunami Warning Center — “Earthquake: South America,” underscoring the importance of recognition and preparedness efforts.

To be sure, there have been great advances in the ability to detect and record earthquakes and quickly determine important earthquake information. As significant as these are, even greater improvements have been achieved in telecommunications and rapid distribution of information.

The earthquake alert at PTWC was followed by the creation and dissemination of a stream of emails, text messages, Tweets and Web pages relating to this magnitude 8.2 earthquake that struck the northern coast of Chile, offshore from the city of Iquique, at 1:46 p.m. HST. Owing to the availability of data collected in the vicinity of the earthquake, PTWC determined preliminary location and magnitude of the earthquake in less than three minutes following the initial shaking.

In Hawaii, we need to be concerned about potential tsunamigenic earthquakes occurring anywhere in the Pacific basin; however, because of past tragic experiences in Hawaii, large earthquakes along the Aleutian Islands to the north, where the earthquake occurred and produced the 1946 tsunami, or in Chile, where a magnitude 9.6 earthquake caused the 1960 tsunami, might create a little more anxiety here. The 1960 tsunami earthquake released more than 30 times the energy released by this year’s April 1 earthquake.

Within half an hour of this year’s April 1 earthquake, a tsunami wave was reported to have struck Iquique, Chile, and nearby areas. Concerns quickly shifted to how the tsunami would proceed. What would the extent of its impact be? Would it be necessary to evacuate people from low-lying coastal areas throughout the Pacific region and undertake other possibly costly preventative measures?

Historical experience offers important clues to go along with modern observations and data. An earthquake struck Iquique in 1877 and sent a tsunami that destroyed dozens of homes in Hilo and killed five people. On the other side of the Pacific Ocean, hundreds of people were killed in Japan by this tsunami.

It is difficult to compare the two Iquique earthquakes in detail. This year’s earthquake occurred in essentially the same source region as the 1877 earthquake, but the 1877 earthquake was somewhat stronger. The fact that the source region of the 2014 earthquake had previously produced a devastating tsunami was also of concern to PTWC with regard to their advisories and warnings.

Since the Indian Ocean tsunami disaster in 2004, along with advances in instrumental monitoring and observation, considerable effort has been dedicated to developing more detailed and improved models of tsunami behavior. Though models are based on assumption and approximation, they can provide useful insights.

While monitoring the progress of the tsunami through the hours following the earthquake, PTWC also ran computer models of how the tsunami would spread across the ocean. Armed with data from deep-ocean water gauges and their model calculations, PTWC became confident that the likelihood of a devastating tsunami hitting Hawaii was low and decided to hold back orders to evacuate. At the same time, because they were still tracking the waves, they stood by their advisory for people to keep out of the ocean for hours after the first tsunami wave arrivals. No sirens were sounded.

Fortunately, damage and losses caused by this year’s earthquake and tsunami were not widespread. At the same time, we are sorry for those who did suffer casualties. We commit our efforts to a better understanding of geologic hazards and to the memory of all who have suffered from natural disasters.

Kilauea activity update

A lava lake within Halemaumau produced nighttime glow visible via HVO’s webcam during the past week. As of Thursday, the lava level for the week had only minor fluctuations, generally staying around 144 to 157 feet below the rim of the overlook crater.

On Kilauea’s east rift zone, the Kahaualea 2 flow continued to be active northeast of Puu Oo, slowly moving through remote forest. The active flow front was 5.2 miles northeast of the vent on Puu Oo as of Wednesday. Webcam images indicate that small, lava-sparked forest fires continue to burn.

There were no felt earthquakes in the past week on Hawaii Island.

Visit the HVO website for Volcano Awareness Month articles and Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos, recent earthquakes and more; call 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov.

Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.