Magical construction and defenses in Tsunami country

[Jasonft]

How would magic affect living in tsunami vulnerable areas?

How would things change for defending against or even CAUSING tsunamis?

I suppose it would depend on the magical traditions involved for a start. Even then, I think some constants would remain.

Detection. Any group with access to decent Earth magic and/or divination should have earthquake detectors built. ESPECIALLY if someone in the area that doesn't like you much can cause earthquakes. Or even cause tsunamis directly.

What forms should they take?

Really over fortified heavy walled construction (churches, forts, governmental) for important buildings that will likely be on hills if possible and probably central to the settlement. Storage silos for grain and other supplies also come to mind. Include ladders and stairs (with really strong handholds) for panicked climbers and make sure any lower level doors/ windows are either extremely solid or non existent. Certainly they would not be on the side facing the ocean.

What forms should these take in various settings?

Earthworks. Really important ports might even go for artificial seawalls and large earth berms to deflect or absorb the force of an incoming wave. Building them big enough and strong enough would be difficult but not impossible with sufficient effort and expense. Bonus: Makes your harbor a lot more secure against pirates and enemies if the entrance through the heavy wall has troops and heavy weapons.

Same question as before - would any of these thoughts apply in your favorite settings?

And last but not least, how does the interactions of magic and tsunamis affect wars? Japan during World War 2 calling down a huge earthquake to surprise attack everyone else in the Pacific basin while warning their own troops ahead of time would be wonderfully vicious (and effective!).

Expensive to do magic on this scale, but likely necessary with humans being humans. I have this moderately horrible image of the British (or the equivalent) trying to expand their colonial holdings eastward from India and finding out what happens when you **** of the backwards natives who have centuries old pacts with volcano gods. It gets nasty real quick.

Anyhow - enough rambling on my part. What do all of you think of the ideas presented for consideration?

[Toptomcat]

By 'magic', can we assume you're talking about standard GURPS magic, and not one of the other variant systems? How common and accepted are mages?

[ericthered]

Originally Posted by Toptomcat

By 'magic', can we assume you're talking about standard GURPS magic, and not one of the other variant systems? How common and accepted are mages?

I think he's intentionally not specifying the magic system.

There are really two concerns:

1) What mundane measures do you take to live in an area where Tsunami's are not only possible but happen multiple times in a generation?

2) What types of magic are most effective against a tsunami?

Another consideration is what causes these tsunamis? If you just live in an area with normal Tsunami frequency, people will probably continue to build in dumb areas. Its just human nature. Magic may give some defenses, but I have a hard time beleiving they'll go to much more effort than modern folks.

If Tsunami's are a weapon of war, then it may be hard to predict specific attacks, but easy to know the year you will be attacked. When war breaks out people will pull back from the coast and store their things someplace safer. Key installations, such as military ports (but probably not civilian), may see some defenses built, or just strong construction that allows a quick return to functionality.

If Tsunamis are a regular weather pattern, you will see extreme adaptations, either in where people put things, or magically constructed defenses. You could also see the equivalent of shelters built: Mounds of earth or buildings above classic waterlines, designed for people to quickly go to.

[Bruno]

Originally Posted by ericthered

Another consideration is what causes these tsunamis? If you just live in an area with normal Tsunami frequency, people will probably continue to build in dumb areas.

Tsunami isn't like earthquake or volcano: there really isn't a definition of "a dumb area", unless you mean "all ocean coasts with any kind of geological activity somewhere in that ocean" - and if so, this would mean the entire west coast of the Americas (North and South), and the entire east coast of Asia, and all the Pacific islands, AND most of Australia would need to be evacuated. Just for starters.

The problem is that the problem area is somewhere else, and then the tsunami radiates out from there.

Putting the Pacific on a "100 mile exclusion zone" wouldn't even solve the problem, it's not like that's the only exciting bit of geology attached to a body of water. More localized tsunami-like phenomena can be caused by landslides and glacier collapse, and relatively minor events can be radically magnified by quirky local terrain.

[Jasonft]

I was deliberately not specifying a magic system because I know some variants seem to work better at causing natural disasters. Also, situations where different groups have different magical traditions would mean different ways of preparing against monster waves.

Still, it seems to me an area worthy of thought. Things like the big Indonesian tsunami some years back could easily cripple an empire if it hit at the right time.

[ericthered]

Originally Posted by Bruno

Tsunami isn't like earthquake or volcano: there really isn't a definition of "a dumb area", unless you mean "all ocean coasts with any kind of geological activity somewhere in that ocean" - and if so, this would mean the entire west coast of the Americas (North and South), and the entire east coast of Asia, and all the Pacific islands, AND most of Australia would need to be evacuated. Just for starters.

The problem is that the problem area is somewhere else, and then the tsunami radiates out from there.

Putting the Pacific on a "100 mile exclusion zone" wouldn't even solve the problem, it's not like that's the only exciting bit of geology attached to a body of water. More localized tsunami-like phenomena can be caused by landslides and glacier collapse, and relatively minor events can be radically magnified by quirky local terrain.

You overestimate what tsunami's destroy. Going for the local high ground is really quite effective at surviving one, and that implies they don't go hundred of miles inland. I doubt most tsunamis go a single mile inland.

The problem is that people are really really fond of building things like cities right next to the ocean. I suspect just about any hill will keep you safe. But that's not where people build.

[Bruno]

Originally Posted by ericthered

You overestimate what tsunami's destroy. Going for the local high ground is really quite effective at surviving one, and that implies they don't go hundred of miles inland. I doubt most tsunamis go a single mile inland.

They go up rivers, and roll over lowland ground like marshland and deltas. You probably shouldn't build in marshland and deltas either, but you can be pretty far from the sea on not lowland and have the wave show up.

Tsunamis go as far as 10 miles inland - not counting being funneled into a river channel. Hurricanes can produce storm surges that go shockingly far inland (and again, not counting any part where they go up a river channel). Multiplying that by 10 is an engineering safety margin habit I picked up from picking ropes for breaking strength - you go with a 10x margin when lives are on the line, because that covers for human stupidity, like letting the ropes lay out in the sun or rub on rocks (or getting sloppy about settlement rules and letting farmland, shanty-towns, and suburbs spread out because "they don't count").

[Dalillama]

Originally Posted by ericthered

1) What mundane measures do you take to live in an area where Tsunami's are not only possible but happen multiple times in a generation?

Live someplace else. Seriously, it's normal for there to be maybe 6 or 8 seriously devastating tsunamis a century, the world over. If the same place is getting hit by them every decade, it's basically unfit for human habitation.

[Anthony]

Without more information on the sorts of magic involved, there's not a huge amount to say. In the real world, the cheapest option is a warning system, and when a tsunami is predicted you move inland/uphill, then go rebuild when it's done, and doing the same thing with magic also works.

[Refplace]

I think its pretty well covered.
Divination to warn of their coming.
Seawalls where you dredge the harbor and pile it up and possibly turn mud to stone would be expensive and likely long term projects but be great as general fortification and possibly fishing and sea farming.
Hills for key parts of the city would be good, a lot of people like living at the top of a hill.