Southwest of Llana Upland lies a fertile region: the Kantol Sea, biggest on Tharn, fully 2500 km (1600 mi) long and 1600 km (1000 mi) wide. With that in mind, let's tour this vast abyssal plain-the biological heart of Tharn. exposing its depths, not just its heights. A very Tharnian gradient! So it's not really small size that gives a world a wide air-pressure range, but aridity. Air pressure would be nearly 5 atmospheres down there, 1.5 on the abyssal plain, two-thirds normal in the ruins of New York, barely breathable in the Alps and Rockies, and nearly Martian atop Everest. if you drained our seas as dry as Tharn, revealing Earth's true ruggedness, Everest would rise nearly 20 km (about 65,000') above the Mariana Trench. True, the air thins out slower with altitude (an effect of low gravity) but overall, both Mars and Tharn have a wider range of surface air-pressures than Earth.Īnd yet. Small worlds with low gravity tend to be quite vertical, and verticality leads to big air-pressure variations. If the Red Planet had a bit more air, you could stroll in Mariner Canyon and Hellas Basin, yet suffocate out on the plains. Air pressure out on the plains is comparable to the summit of Everest but in the deepest trenches, it's merely Alpine-breathable even for Terrans.Īll this is quite Martian. Lewis pictured Mars as a desert world scored by deep gashes (the canals) where water, air and life collected: linear oases. In the early 20th Century science fiction writers like C.S. Most importantly, 'continental' uplands end in rugged coastal ranges, dropping into subduction trenches many km deep the trench floors are usually flooded, but the lakeshores form oases where the air is dense and mild. Mountain-arcs cut off basins of desert and steppe around the edges. Chains of great shield volcanoes rise twice as high as Everest a rift meanders along the west side of the basin, where new crust spreads, forming a long winding fracture zone of rugged, wooded ridges. The Barsoom Basin is startlingly similar-except all these features are laid bare. The Pacific Ocean has trenches and island-arcs around its edges and a rift zone in its heart, as well as the most prominent example on Earth of a shield-volcano chain: Hawaii. Barsoom most resembles central Africa's equatorial rainforest and savannas north and south-that is, if Africa had only Red Seas, Mediterraneans and Sahara Deserts surrounding it! The result is a warm, wooded strip some 7000 km long and 2000 wide (4500 x 1250 mi), flanked by broad savannas, which thins to desert only around 25-30 degrees north and south. And the equator, heated by full-on sunlight, is a zone of rising air as the air rises it cools, generating clouds. the Kantol, Wula and Waroon Seas are puddles by Earth standards, but their surface area is enough to guarantee that any wind brings at least some moisture. These are rarely over 100 meters deep, and usually less. Instead, the 'sea floor' is just a great plain, with salt lakes at the low points.

That's not saying much, of course-if this were Earth, Barsoom would be an ocean, brim to brim. The Barsoom Basin is an equatorial region of seas and forests-the wettest region in the world. Map, Tharn's homepage, Peoples of Tharn, Regional tours, Geology and Evolution, gazetteer, terms explained.

Barsoom map