EVIDENCE FOR LARGE TSUNAMI IN THE TONGAN ISLANDS

While well documented accounts of large tsunami in the Tongan Islands do not seem to exist, there are reasons to believe that large tsunami have occurred there in the past. Besides a strong oral tradition among some of the elders of a peau kula or “red wave” that can cover a whole island at one time, there are contemporary accounts of a few historic events. Also of great interest are some large boulders that are found at various locations on different islands that seem to have been deposited there by prehistoric tsunami. These waves were probably generated by local events such as volcanic eruptions, earthquakes and submarine landslides produced by activity in the Tongan subduction zone. Local traditions say the boulders were placed on Tonga by Maui.

A tsunami with a 2.5-meter run-up has previously been reported for the Ha’apai Islands after the April 30, 1919 (Ms 8.0) earthquake. The epicenter was about 160 kilometers east of Vava’u in the Tongan Trench. A written account of this tsunami reaching Otualea Beach, Vava’u has been recently discovered in the personal history of a Tongan who was there in 1919. According to his story, a large “tidal wave” struck the shoreline east of Ha’alaufuli and climbed “nearly half way up the cliff” while “fish, sharks, and sea life of all kinds were thrown on the tree tops.” From his description, it appears as though the run-up could have been as high as 20 meters or more. A small village of beach houses was destroyed, but no one was killed or injured. The earthquake that created this tsunami may have also generated a submarine landslide on the southwest flank of the nearby Capricorn seamount. Another “large wave” has been reported on the island of ‘Eua that occurred around 1959. This wave washed a large boat ashore at ‘Ohonua.

Further evidence for large tsunami may exist where large boulders have been deposited on land. Two such boulders exist on Tafahi; others are on Vava’u, Ha’apai and Tongatapu. The largest one examined was found near the town of Fahefa on the southwest side of Tongatapu. It is a well-rounded limestone boulder about 15 meters in diameter and weighing about 2,500 tons. There are at least 9 other smaller boulders sitting on the ground in the town of Haveluliku on the east side of the island. They are of special interest as they are located about 25 meters above sea level and about 450 meters from the shoreline.