ANGEL FALLS IN CANAIMA NATIONAL PARK, VENEZUELA, 3212 FEET (979 METERS) HIGH
The plaana are much the same as Earthly plateaus -- the tepui table mountains of Venezuela, for example -- merely much, much higher above the lower land forms. Eight to ten kilometres up, the plaana environment shares little in ecology or climate with the lowland hyperjungle.
The plaana are surely not without precedent in the universe. Within our own Solar System there are many outstanding examples of extreme topography. For example . . . .
Miranda – Smallest moon of Uranus (292 miles in diameter), was shattered billions of years ago by repeated collisions with asteroids. It regrouped but melded incompletely due to too-low temperatures. One of its highest escarpments is 19 kilometres high.
Ariel – Brightest moon of Uranus, 718 miles in diameter, is scarred by extensive canyons and crevasses, some hundreds of miles long and six miles deep, and by craters. Canyon walls and floors have been polished smooth by rivers of liquified methane, ammonia, or carbon monoxide, driven to the surface by the heat of radioactivity in Ariel's core or by tides raised by the gravity of the other moons. [Discovery mag., July ‘99]
Ganymede – This Jovian moon features Galileo Regio, rifted, parallel mountain chains running for hundreds of kilometres, cracked open when the surface expanded and resulting tectonic shifting occurred to vent heat from the core.
Titan – Largest moon of Saturn, may hold accumulated the solar system's richest store of organic molecules in a polymer sludge hundreds of metres thick on its surface, accumulated deposits of nearly 5 billion years, waiting for release from Titan's minus 290 degree freezer.
Mars – Valles Marineris (formerly Coprates Canyon) is an example of troughed terrain, a collection of canyons 4800 kilometres long, 240 kilometres wide and up to six and a half kilometres deep caused by tensional rifting, then enlarged by wind-blown sand erosion. Also, rifts in the ice polar packs may easily reach several thousand metres deep.
Mercury – This innermost planet has examples of lobate scarps over 3 kilometres high resulting from global cooling and contraction of the thin crust. It also has Caloris Basin, a 1280-kilometre-wide crater with walls over one and a half kilometres high. It is the impact site of a meteoroid that hit hard enough to cause fracturing of the direct opposite side of the planet.
