## Tidal implications of eccentric planetary orbit

Lots and lots of fiddling payed off at last: Proof of concept! (warning - takes a bit of patience)
 (continued from post #7) Tsunamis: Tsunamis are a means of carrying away the bulk of the energy liberated by landslides into (or underneath) the sea. A popular worst-case scenario for such a landslide is the sudden and total failure of one flank of the Cumbre Vieja volcanic ridge in the Canary Islands. The article gives estimates of the physical quantities involved, which allows us to calculate the gravitational potential energy available to fuel the tsunami:Etsunami ~ Egrav|initial - Egrav|final Etsunami ~ G Mearth Mlandslide (1/(Rearth-Hsea) - 1/(Rearth+Hmountain)) Etsunami ~ G Mearth Mlandslide ((Hmountain+Hsea) / ((Rearth-Hsea) (Rearth+Hmountain))) Etsunami ~ G Mearth Mlandslide ((Hmountain+Hsea) / Rearth^2) Etsunami ~ (7*10^-11 m^3/kg/s^2) * (6*10^24 kg) * (10^15 kg) * (1 km + 2 km) / (6*10^6 m)^2 Etsunami ~ 3*10^19 Jwhere the H are estimates of the characteristic height of the pre-slide mountain and depth of the off-shore oceanic basin, respectively. According to one of the scientific publications linked from the article, this tsunami would expend most of its energy on the Eastern shores of North America and Northern South America. There, it would cause ~15 metre waves for a duration of ~15 minutes, which corresponds to a power density (power per unit length of coastline) ofLtsunami ~ (3*10^19 J) / ((15 minutes) * (10,000 km)) ~ 3 GW/mCorrespondingly, the mean power density of my tides is given byLtidal ~ (10^18 W) / (40,000 km) ~ 30 GW/mSo, by this comparison, the impact of the perihelion tide is comparable to that of ten tsunamis of ~15 m, or, assuming the dependence of wave power on the square of the wave height applies to these as well as to surface waves, a single tsunami of something like ~50 m. That seems a little bit at odds with the previous result of ~10 m ordinary waves - but not grossly so, as those have a frequency an order of magnitude higher. Anyway, the important implication is the same - at this energy content, the tide should be able to devastate everything below the high-water mark, but should not be able to propagate significantly farther inland than that high-water mark on sheer inertia. For tsunamis, the limit seems to be some tens of kilometres, depending on the height of the waves and the steepness of the coast.

Thanks for that! I'm going to wait and see if others can shed some light on the various questions you raised before replying in detail, except for the two points below:

 Quote by JohnRC I was a little surprised by the account of tidal locking in the original post, but it certainly seems to be in accord with the wiki article.
I've more or less adopted mfb's suggestion from post #14 regarding the white dwarf, i.e. that it only recently became part of the solar system by ejecting one of the components of the original binary and usurping its place, and that the planet's orbit only became eccentric as a consequence of that encounter. Positing that that transition was (just) survivable means that the orbit only has to have undergone tidal resonance effects for as long as it would take the biosphere to recover from that upheaval, which reduces the timescale by maybe two orders of magnitude. That makes things more plausible in that regard, surely.

 Quote by JohnRC [T]wice daily pressure changes that would span at least a factor of 2 in local atmospheric pressure, and possibly much more.
I wondered about that initially, but something I read in the meantime (can't remember what, unfortunately) gave me the impression that the pressure would remain constant, to first order, because the atmospheric tides, like the ocean ones, are primarily flows towards an equipotential state. Thus, the increased height of the air column overhead during "high tide" is exactly (again, that's to first order) counteracted by the reduced weight of that air. Does that make sense to you, or did I misunderstand something there?
 Sorry, but I have just realised that to get 1000 times the energy into a wave, the wave would only have to be √1000 = 30 times as high, not 1000 times. So the effects of water tides would not be nearly so drastic as in my last post. But tidal effects on the oceans would still be quite severe enough to lead to some catastrophic problems. It would be beyond my knowledge of fluid dynamics to work out how a global tidal bulge which scaled directly with height onto energy would interact with local-ish wave effects that would scale as height with √energy
 ^ Yeah, that's what the first bullet point in my OP was asking as well. Unless someone tells me otherwise, I'm just going to assume that local variations in tide amplitude can be ignored. To increase it by an appreciable amount somewhere other than in a narrow fjord or some such, you'd have to move a hell of a lot of extra water to the place in question from somewhere else, and it doesn't seem reasonable to assume that fairly shallow coastlines could cause that amount of flow, it seems to me.