Dynamic Planet Part 7
Community Contributed by G.T. Larson
On a cold winter night along the northeast coast of Japan, the stillness of the night was broken by the rushing of water. The sea had receded and then came ashore in a long series of waves, reaching over 15 feet high. Up and down the coast, towns and villages were affected; ﬁelds and farms were awash. But all were taken by surprise by this event; an event very familiar to the country who gave the modern scientiﬁc community the name tsunami to describe seismic sea waves.
The Japanese, for a long time, have been very meticulous in record keeping; hence we know the tsunami hit at midnight January 26, 1700, without warning – the warning normally being an earthquake. It came to be called the Orphan Tsunami, no one knew its parent. It was not until the 1990s that the Orphan Tsunamiʼs parent was established; the Cascadia Subduction Zone earthquake had generated a huge tsunami along the northwestern coast from northern California to Alaska and subsequently, Japan. But this was not the ﬁrst orphan tsunami.
Back in dim recesses of time, when the island of Molokai was at its largest in landmass, the north shore was a gently sloping shoreline like our present day south shore. At some point, probably due to a combination of several factors, a large part of Molokai became unstable. There was an east-west rift zone along the crest of the east Molokai volcano. The tremendous amount of rainfall along the north east coasts of all the islands keeps our rainforest luxuriant, but all that water can, if conditions are right, act as a lubricant to unstable slopes. A fault movement triggered a massive earth movement, more properly referred to as a mass wasting event. Almost half of the island of Molokai, in one massive slide along the east-west rift zone, disappeared into the Paciﬁc Ocean.
Later, erosion, land subsidence (sinking) and wave action continued the sculpting of the magniﬁcent sea cliffs Molokai is world famous for. The sea cliffs’ origin comes from what scientist call the Wailau Slide. As this tremendous amount of debris suddenly entered the ocean, a wave, a mega-tsunami, rose to tremendous heights. Some estimates have a 2,000-foot wave washing over parts of west Molokai. Huge waves wrapped around the east and west ends of Molokai, most likely hitting Lanai, Maui and Oahu. It has been estimated that the tsunami, after traveling across the Paciﬁc, would have impacted the California coast with 30- to 60-foot waves, and waves from 25- to 30-feet in the Paciﬁc Northwest, Vancouver Island and Alaska. Though there no one was there to witness this catastrophe, this Orphan Tsunami and its parent, the Wailau Slide, left its witness today, for all to see and be awed by.
We live upon a dynamic island, in a vast ocean and on a dynamic planet. Get outside and let the outside in you. Aloha Ke Akua.