WAVES HIGHER THAN MONAS

Megatsunamis – the threat we can’t flee                          

No imagination needed to know why William Dampier named the westernmost part of Australia Shark Bay. 

The English explorer and naturalist would have marveled at the wildlife back in 1699. It’s still there in what is now a World Heritage Site, 830 kilometers north of Perth. Apart from the predators, thousands of dugong and dolphins thrive in the globe’s largest seagrass meadows.

Smart observer though he was, Dampier either didn’t notice the huge limestone blocks sitting incongruously on the flat surface of an island, or thought them unworthy of record.

Three centuries plus ten years later, the State’s most senior geologist Dr Phil Playford, came, saw and pondered their presence.

What he discovered should send all Indonesian coastal dwellers packing their belongings and heading for the interior right now.

The huge boulders, some estimated to be 700 tons, had been smashed off the coastal cliffs.

They were then gathered by a giant wave, chucked 250 meters inland and dumped 15 meters above sea level.  The only force that could have rearranged the landscape so dramatically would have been a tsunami.

However not like those last year in Palu and Sunda Strait.  Though devastating and tragic, they were just ripples in the sea when compared to the megatsunamis which clawed and pummeled the West Australian coast.

Remember the lead character in the Peter Jackson movie King Kong picking up trucks and planes, then tossing them like tennis balls?  To get some idea of megatsunami might, make the monster gorilla ten times bigger and stronger, but minus the romantic interest and compassion it showed to the heroine Ann Darrow.

When the late Dr Playford’s research was published he said dating the rocks had shown that while most were moved between 2,900 and 5,000 years before the present, one upheaval was only six centuries ago.

The mammoth waves weren’t confined to Shark Bay.  Over time they shaped 3,500 kilometers of the continent’s northwest coastline, leaving some of the world’s largest megatsunami deposits.

These awesome events weren’t conceived in Australian waters; they began when the Indonesian Archipelago’s geology shrugged itself after its regular little lie-downs.

Playford suggested the awakenings were underwater volcanoes or massive landslips, like the slope that fell off the side of the Anak Krakatoa volcano in December.  An asteroid plunging into the Indian Ocean is another possibility.

Australia’s land mass is relatively stable; it’s not part of the Ring of Fire circling the Pacific and Indonesia. The continent’s few mountain ranges were pushed up millions of years ago.  Many have been eroded down to hills by the actions of wind, rain and sun.

There are no active volcanoes.  There have been earthquakes, but usually small and rare in built-up areas.

Around 1,000 people live permanently in Shark Bay settlements; thousands more visit during the winter months to fish and sightsee. If another megatsunami hit there’d be deaths, though not on the scale of suffering in Indonesia where millions live on or close to the coast.

The most recent megatsunami was in 1980 at Spirit Lake in Washington State when the Mount St Helens volcano exploded.  Water surges up to 250 meters were reported; fortunately this was a sparsely populated area so the death toll was only 57.

Twenty-two years earlier and also in the US, a landslide at Lituya Bay caused by an earthquake sent a 524 meters high mountain of water surging across the land, tearing down  forests in the Alaskan wilderness.  Once again there were no population centers nearby so just two perished.

But the most awesome megatsunami in recorded history was in 1833 when Krakatoa blew up in the Sunda Strait. Pressure waves circled the globe three times.

The bang was heard in Perth, 3,000 kilometers distant; it was reckoned to be four times greater that the largest human-made explosion ever. This was the Soviet hydrogen weapon Tsar Bomba detonated in 1961 at an Arctic Ocean test site.

About 36,000 may have been killed by Krakatoa and the ash fallout, which darkened the heavens for days. That number is suspect as communications were then primitive and there was no centralized disaster agency to count corpses.

Java is now the most densely populated island in the world. Even if all the early-warning system reforms promised by the government are implemented, they’ll offer no protection against a megatsunami.  That’s because there’s no coastal high ground safe against waves several times taller than the 132 meter Monas.

Consider the facts:  Jakarta is eight meters above sea level.  Surabaya, the Republic’s second largest city is just five meters, the Juanda international airport only three meters.

The nearest safe center in East Java would be Malang, 444 meters and far enough from the coast for the energy of any megatsunami to dissipate as it rushed across the land.  But the city is surrounded by mountains, including the highest in Java.

Semeru, 3,676 meters, has blown-up 56 times in the last two centuries.   It semaphores its power every morning as it puffs like a steam train.  The fine ash dusts everything, including the keyboard used to write this story.

Just a daily reminder that in this country we puny humans are forever at the mercy of nature. 

First published in The Jakarta Post, 9 March 2019

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