Poetically and almost literally, Kainui’s mantle is at endless war with its overlying ocean. Perhaps they are simply too intimate; they confront each other directly, with no identifiable intervening crust. The underside of the interface is not quite liquid most of the time; the upper is technically gas, since the ocean at that depth is far above water’s critical temperature.

What pass for tectonic plates, from township to county size, are solid enough to crack and tilt and be carried as individual units by mantle convection. Tsunamis are generated constantly, sometimes by abrupt plate shifts—quakes—sometimes by vulcanism, though there is nothing at all like a Terrestrial volcano on the world.

When magma emerges from the mantle to become lava and meets the sea there is of course violence, but Kainui has never experienced a Krakatoa-type steam blast. The weight of twenty-eight hundred kilometers of water, nearly all of it far saltier than any Earth ocean, provides some eighty thousand atmospheres of pressure. A few hundred kelvins rise in temperature has no real effect on either phase or volume.

So when, one day, a tenth of a cubic kilometer of glowing liquid silicate was suddenly exposed to ocean bottom along the line between two spreading plates, the result was merely a linear-source sound wave.

Its front spread out as wave fronts do, trying to become flatter and flatter as it left its source behind. It failed miserably. It passed through layers of differing salinity, temperature, and tonnage of suspended matter. Sometimes locally it turned concave and was focused so narrowly as almost to regain its original pressure. Sometimes it diverged, but its total energy degraded only gradually toward heat.