The dust chasms or dust basins were a weather phenomenon of Arrakis, produced by geological processes, being subsequently filled with dust.
They were a hazard to unwary travelers because the dust had a quicksand-like behavior. The dust packing was so under-dense that tidal motions much like oceanic tides were readily observable (locally called sandtides). In other words the dust exhibits almost negative packing, hence fluid-like behavior; similar situations have rarely been found on any other planet.
The sequence of events is as follows:
- Dust deposited after each storm was highly charged. Also, grain surfaces contained absorbed water vapor.
- The number of negative electrons and positive ions was initially about equal within the dust mass.
- The electrons attached themselves to the highly polar water-vapor molecules.
- The water-vapor molecules migrated up ward along the atmospheric density gradient. The ultraviolet rays then desorbed the water vapor, returning it to the atmosphere, together with the negative charges.
- The positive ions were tightly bound to the distorted surface lattice of the dust grains and remained behind.
- As a result the dust had a strong and highly stable positive charge. The repulsive electrostatic forces almost equaled the gravitational forces, hence the fluid- like behavior.
- The dust layer built up in depressions and chasms after this fashion until they were filled. Of course as the layer thickness increased, the weight of the overburden caused compaction. Hence the quicksand-like behavior was confined to the upper five meters (approximately) of the deposit.
These phenomena were not observed in exposed areas since any charge inequality on dust deposited there was quickly neutralized by subsequent motion over the surface and prolonged exposure to ultraviolet. only a small percentage of neutralized dust was present in the chasms and basins. The charged zones had no influence on the behavior of neutralized dust or sand moving over them. In fact the first few tenths of a millimeter of the dust oceans was neutralized by ultraviolet exposure.