Volcano Watch — HVO's role in the history of tsunami prediction in Hawaii?

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April is Tsunami Awareness month, a reminder of Hawai`i’s most deadly tsunami, which killed 159 people on April 1, 1946. The tsunami was generated by a magnitude-7.8 earthquake beneath the Aleutian trench.

HVO's role in the history of tsunami prediction in Hawai?i...

HVO's role in the history of tsunami prediction in Hawaii?

(Public domain.)

While there is no reliable way to predict earthquakes yet, there are reliable ways to predict many tsunamis. The fundamentals of the prediction method were worked out nearly a century ago by Thomas A. Jaggar, the founder of the Hawaiian Volcano Observatory (HVO).

Jaggar knew that submarine earthquakes generated tsunamis. His growing network of volcano-monitoring seismometers also detected large, distant earthquakes that could potentially generate tsunamis.

Once HVO had installed seismometers in Hilo and Kona, Jaggar could determine the approximate location of distant earthquakes (as well as the local ones) and was ready to do some predictions. As a test, he privately predicted a tsunami following a Chilean earthquake in late 1922. The tsunami arrived on schedule, and he was ready to go public.

His chance to put it into action came on the morning of February 3, 1923. During his first inspection of the seismic records, he saw that a large, distant earthquake had been recorded about an hour-and-a-half earlier. Quickly calculating that a tsunami could be expected around noon in Hawai`i, Jaggar notified local authorities but, unfortunately, was not taken seriously. The tsunami arrived anyway. Much damage was done to boats, wharves, and shoreline embankments; one fisherman was killed. A Matson freighter was forced aground in Kahului harbor on Maui.

People in Hilo were much more receptive to Jaggar’s next warning following an Alaskan earthquake on October 24, 1927. Several businesses along the Hilo waterfront secured their belongings, and the entire fishing fleet moved out to deeper water. This time, the predicted tsunami failed to materialize. It was later determined that the earthquake actually occurred 100 miles inland and could not have generated a tsunami.

Jaggar’s approximate location had not been accurate enough to determine whether the earthquake had been truly submarine, a necessary condition for the generation of a tsunami.

Another prediction and warning of a tsunami from Japan in 1933 was taken seriously. No lives were lost, and damage was minimal despite a maximum trough-to-crest wave height of 17.5 feet at some west-facing shore of Hawai`i Island. The tsunami warning system seemed to be working well for Hawai’i.

Yet on Monday, April 1, 1946, a tsunami hit Hilo Bay just before 7 a.m., killing 96 people in 2 hours. A total of 159 people died throughout the state in probably the greatest natural disaster Hawai`i has known.

Why was no warning given in 1946 that might have prevented the great loss of life? The answer is surprisingly simple.

The distant earthquake that announced the April 1, 1946, tsunami to follow was recorded at 2:06 a.m. Hawai`i time, but was not discovered until 7:30 a.m., when staff reported for work, a half hour after the waves had started to hit Hilo! In 1946, there were no more than four people on HVO’s payroll to keep everything running. Then, as now, HVO was a Monday-through-Friday operation.

In direct response to the disaster, Congress funded the creation and operation of an entirely new agency within the U.S. Coast and Geodetic Survey, called the Seismic Sea Wave Warning System (SSWS), now the Richard H. Hagemeyer Pacific Tsunami Warning Center (PTWC), located at Ewa Beach, O`ahu. HVO continued to provide tsunami warnings for Hawai`i until SSWS was operational in 1949.

HVO technicians solved the problem of how to provide around-the-clock monitoring with limited staff. In December 1946, they installed a buzzer that went off at the Observatory and in two staff residences when seismometers detected a distant earthquake large enough to generate a tsunami. Even in the middle of the night, the buzzer would roust someone out of bed when a large, distant earthquake occurred.

The current PTWC staff is alerted in much the same manner, now, to a possible tsunami. Their sensor networks are much more extensive and include tide gauges, deep-ocean tsunami-detection buoys, and the combined seismic instruments of the Global Seismic Network (GSN), USGS National Earthquake Information Center (NEIC), and the Hawai`i Integrated Seismic Network (HISN). Their area of responsibility is much broader, including the entire Pacific and Indian Oceans, The South China and Caribbean seas, and Puerto Rico and the U.S. Virgin Islands. Their analysis is more accurate, more complex, and quicker.

But Jaggar’s HVO continues to support tsunami detection and warning in Hawai`i by making our seismic network available through the HISN.


Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have remained at background levels. The summit caldera has been expanding, indicating inflation, since the beginning of 2007. The number of earthquakes located in the summit area is at low levels (usually fewer than 10 per day are large enough to locate). A small flurry of earthquakes is occurring in the south flank in the vicinity of `Apua Point.

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater. There have been several small flows from the MLK and Puka Nui vents on the west flank of Pu`u `O`o in the last several weeks. Lava is fed through the PKK lava tube from its source on the southwest flank of Pu`u `O`o to the ocean. About 1 km south of Pu`u `O`o, the Campout flow branches off from the PKK tube. While the PKK tube appears to no longer be active below the top of Pulama pali, the Campout tube is the source for the dominant ocean entry at Kamokuna inside Hawai`i Volcanoes National Park.

In the last week, intermittent breakouts from the Campout and PKK tubes have been seen on the slope of Pulama pali. These spectacular breakouts have been described as some of the best seen in several months. Below the pali, a western branch of the Campout tube continues to host surface flows several hundred meters inland from the sea cliff at East Lae`apuki. An eastern branch is the source of lava ponding at the base of the pali at the bottom of Royal Gardens Subdivision.

The National Park Service has placed beacons leading to the active lava inland from East Lae`apuki. This is the closest lava to the end of the Chain of Craters Road in Hawai`i Volcanoes National Park. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-3.1 earthquake occurred at 1:42 a.m. H.s.t. on Saturday, March 31, and was located 22 km (13 miles) northwest of Kawaihae at a depth of 16 km (10 miles).

Mauna Loa is not erupting. Two earthquakes were located beneath the summit. Extension of distances between locations spanning the summit, indicating inflation, continues at steady slow rates.