A dune sea is unpacked sand sculpted by wind into enormous shapes. Satellite imagery of the Sahara dune sea discovered an ancient large dry lake. The distance from the lake bed to the dune top was estimated at 110 feet, and a 3 mile wide base. A land rover using sand tracks can make it up and down them. As can people carrying a light load (think IG conscript), but a space marine (do to pounds per square inch) can quickly be hip deep. A battle cannon firing could (on a six) cause a liquefaction event, burying it. A FW four barrel super fusion cannons wouldn't just sink, but encase most of it in a fresh coat of glass! In a game it's lost, but in a campaign it can be dug up, hauled back to base, and refurbished. If you retain the area!