Question about superatmospheric mesas.

[gilgamec]

In the 16th and 17th century there were many white spots on the maps (especially around Antarctica). On the other hand: 25000 meter high mountains are visible from very far away, but they may be mistaken for lower mountains that are closer.

On an Earth-sized planet, you'd be able to see a 25km high mountain (or it'd be above the horizon, at least) for about 550km, or about 5 degrees; that's only up to (at most) the Arctic circle, which is a pretty high latitude. If the longitude of the pole was a long way from the European analogue, it's quite feasible that it wouldn't even have been noticed by them until the early modern era -- think something like the European exploration of Alaska or eastern Siberia, which weren't until the late sixteenth or early seventeenth century.
Of course, unless the coast was completely uninhabitable, there might be some human settlement -- though some parts of our own Arctic weren't settled until close to the modern era.

[Turnpikelad]

The mesas are not being held up by their own structure - they would collapse/ sink into the mantle really soon if that were the case. They're being held up by a constant welling up of energy along the magnetic poles of the planet. Although the planet has a floating crust, the mesas are thick cratons that have been fixed to the magnetic poles for billions of years (since the formation of the planet). They may rotate a bit over time as the land moves around them, but they probably contain some material that attracts to the very strong telluric (bull**** word but it'll do) field at those points. The magnetic poles do not wander nearly as much as those on Earth, although the polarity switches a few times per million years - with temporary catastrophic results.

I want the coastline of the Patagonia-like region bordering the northern mesa to have been charted by Thurian explorers, but I don't want them to have realized that the adjoining mountain range is actually five times as high as a regular one. Do you think it would be possible that the continual glaciation has carved away the slopes of the mesa enough that the curvature of the world prevents a traveller at sea level from truly seeing the unbroken limb of the central plateau on the horizon, instead seeing a jagged, glaciated mountain range?