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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