nerdsniped wrote:keithl wrote:Safety of various shoreline places:
The volume of the Mediterranean is 3,750,000 km3, the average depth is 1,500m, so the average distance the water falls is 750m. The energy generated by filling that huge volume with water is 3.75E6 km3 x 1e12 kg/km3 x 750m x 9.8 m/s2 or 2.7e22 joules.
What happens to all that energy?Spoiler:The Reynolds number through the Gibraltar gap is enormous ( inertia effects >> viscosity effects ), and even larger through all the various gaps between mountains and islands - it will take a very long time for the energy to dissipate in viscosity, evaporation, etc. So water pours in through the gap, water accelerates throughout the Atlantic towards the gap, develops a lot of momentum, pours into the Mediterranean basin - and keeps moving, long after 3,750,000 km3 has passed through. It's like releasing a weight suspended by a spring; the weight will drop, bounce on the spring, and bounce back above the original level of release.
Well, that's what's going to happen with a Mediterranean's worth of water, until there's been enough Time to couple all that potential and kinetic energy into viscosity and evaporation. And like the bouncing spring, the water may have waves as high the the Mediterranean is deep. Indeed, given the complex reflections off the irregularly shaped bottom and sides, there may be waves even higher. There may be sporadic waves lapping up to the Pyrenees, the Alps, through gaps in the Apennines entirely across Italy. This is NOT an overdamped system.
Much depends on how big a gap is torn through GiIbraltar - for major, impossible-to-flee-on-foot changes to occur in days or even weeks, the gap must be large and the acceleration of the seawater stupendous. At those scales, the "overflow" and rebound waves will be far higher than Chateau d'If, a few meters above sea level.
Here in Oregon, there is sand on tops of 100 foot cliffs from the 1700 AD tsunami, caused by a 9+ earthquake in the Cascadia subduction zone. We know exactly when that tsunami happened, because the waves reached Japan many hours later and killed people. It wiped out almost all of the near-shore Indian tribes in the Pacific Northwest, and only chance topography saved a few tribes farther up the hills. These enormous subduction zone quakes happen about every 300 years. One is likely to happen before this wiki posting goes off line, and I expect some enterprising but idiotic reporter will find this posting after that terrible event, and create mass panic in Italy.
It does seem like the castle is not going to be a wise place to ride things out, even if it is known to be above the ultimate sea level...
I don't have a lot of analysis to back it up, but this seems like an overestimate of the effects. The mountain ranges north and south of the opening limit the possible flow. A lot of friction will dissipate some of the energy (grinding of rocks, ...) A Mediterranean's worth of water isn't being dumped in all at once at one end. Locally, on the edge of their current sea it will be quite violent, but as it fills, the rate of rise slows.
Anyway. Seems too bad to be true.