Welcome to the New Year, which we may all hope will be better than the old year. Today’s post is about a lesser, but still significant, disaster whose effects have already been seen of late on a small scale and historically on a much larger scale. Mega- tsunamis.
My attitude toward the disasters I’ve discussed so far is a bit different from that of most people. The articles, videos and academic papers I have seen on this subject generally lay out the effects with a greater or less degree of detail, and a greater or lesser degree of breathless horror at the inevitability of it all. I’m going to look at what could be done about it.
This, by the way, is the theme of the Portal Authority series of novels. Worlds in peril, and something effective being done about it. The something being done usually involves large nuclear devices, which in the real world would provoke considerable adverse comment. I do draw from major disasters throughout Earth’s history, and do my best to stick to the known effects of nuclear devices.
But, back to Earth of the present day. There is good solid evidence of mega-tsunamis having occurred throughout Earth’s history. The Chicxulub impact, which put paid on the age of the dinosaurs, brought a variety of dooms upon the life of Earth. One of these was a planetary mega-tsunami which rolled right around the Earth. [source] It is estimated to have been 1500 metres high, according to research at U of Michigan, which makes it substantial even by planetary standards.
Asteroid/comet impact is not the only cause of tsunamis. Water is incompressible, and shockwaves propagate through it with high efficiency. Thus, any major vertical thrust of the ocean floor from an earthquake can, and has, created a tsunami.
The most well known and lethal tsunami in recent history was the 2004 Indian Ocean Tsunami, responsible for the deaths of over 220,000 people around the shores of the Indian Ocean, along with massive damage to homes and infrastructure. The energy release was approximately equivalent to a five megaton nuclear device.
It created a wave 33 metres high, which travelled right across the Indian Ocean and wreaked havoc on the shorelines it struck. Tsunamis in the deep ocean are harmless, just a long deep swell. When they hit the shoreline they raise up out of the water and break, doing massive damage to whatever is in their way.
Landslides also cause tsunamis, though less frequently. Billi, et. al. make the case that the disaster which befell Messina in 1908 was twofold, the earthquake itself and a tsunami caused by an underwater landslide triggered by the earthquake.
Coming to the present day and looking into the future, there has been a controversy about the potential for disaster posed by the Cumbre Vieja volcano on the island of Las Palmas. Ward and Day modelled a worst case scenario which saw waves of tens of metres height coming ashore on the East Coast of North America, which has many large cities in low lying areas. Modelling tsunamis is an uncertain business, but such a worst case is sufficient to get people’s attention.
Ward and Day took as a worst case the collapse of 500 cubic kilometres of rock and soil into the ocean all at once.
Countermeasures
The conventional answers to the prospect of such a disaster add up to Indications and Warning (I&W) and hardening of the targets. The lack of an I&W system for the Indian Ocean was blamed for much of the death toll. Even a few hours of warning allows people to take shelter or reach higher ground.
While this may mitigate the human cost, it does nothing to reduce the damage to homes and infrastructure.
Hardening of buildings and infrastructure is a matter of decades, upgrading building codes and retrofitting buildings as opportunity offers and funds and resources are available. It mitigates the damage, but that damage is still very great. According to the NGO World Vision the toll of dead and missing from a 38 metre wave was over 20,000 and the property damage at $360 billion.
Going back further, the Storegga Slide, off the coast of what is now Norway, involved a landslide of 3500 cubic kilometres of material, inflicting a mega-tsunami on the North Atlantic basin. It devastated the lowlying area known as Doggerland, which is today under the North Sea.
Here is a radical proposal. If a bomb is going to blow up a city, the natural reaction would be to find it and defuse it, or at least trigger it in a controlled and harmless fashion. Why not do that with these natural disasters in the making?
In the case of the La Palma landslide, the unstable material is right out in the open. There’s a lot of it – 150 to 500 cubic kilometres. Chunks of it could simply be scaled off into the ocean, harmlessly. The work would undoubtedly take decades if not generations, but it could be done at an affordable pace, and the cost would surely be far more bearable than the cost of the worst case.
For a novel I currently have in work, I considered a submarine landslide twice the estimated size of the Storegga slide, about 9600 cubic kilometres, which would launch a tsunami at a lowland area about the size and population of Japan.
The pressure on the rock retaining wall between the weight of wet mud on one side and the weight of water on the other side was very substantial, so much so that a single tunnel about one square kilometre in cross section was sufficient to drain the mud, or most of it anyway, into the deep ocean in about three weeks. Yes, they used a nuclear device to excavate the tunnel.
In the real world, getting the consensus together to do something like that would be – well, let’s just say very difficult and time-consuming. It would require a considerable international effort to find the threats, analyse them, and where appropriate drain them. Physically, I think it could be done.
What then of the more common case of earthquakes? It would certainly be a harder problem, but it is known that human activity can produce mostly small and harmless earthquakes. The Hiquake Database lists a lot of them, complete with causes, of which the injection of fluid into the fault is the commonest. It therefore seems to me that it would be possible to defuse a threatening fault over a period of time, with many small quakes instead of one large devastating one.
These are suggestions, not terribly well worked out. Doing something about these threats would entail taking risks.
My military experience has taught me that in a disaster, the worst decision is no decision, and there are no risk-free solutions.
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