Two hexes south, three southwest of Alakran.
We continue the survey of odd geological phenomena to be found at rare occasions in these otherwise unremarkable stretches of sandy desert.
The world Mittellus has no tectonics; it is a cube, or one habitable face of it, the others being too cold, too hot, too wet, too dry, and on the other side of the world. Nonetheless, there are subterranean entities that folklore rightly or wrongly identifies with such beings as the ur-dragon Tiamat, the World Serpent, or the Lord of Devils. These stir occasionally, maybe once in every 125 mile hex every 100-600 years, and shake the surface of the earth in a 25 mile diameter. There is a possibility of more quakes, if the crust of the earth becomes infested with adventuring surface dwellers, who stir up things and places better left alone.
Weird things happen when an earthquake shakes a stretch of sandy desert. The sand becomes liquid -- anyone on top of it will start to sink unless they can grab something that would reasonably float in water. You drown in liquid sand just like in water, with the added feature of being entombed in 5-20' of sand when the quake stops, and taking constant force damage hits from abrasive sand every turn, hitting you with +3 to hit for d8. The liquid sand is swimmable, but who in the desert knows how to swim?
In these already rare events even weirder things have been known to happen, passed on down the generations by the Sandwalker druids. In quakes at night, pale lights shine from under the sand. Sand whirlpools gape, and sand spouts jet up. During a desert earthquake, sand is water, and that's not just a trope!