Filling of the chasms today results primarily from'landslides and rockfalis. The chasms provide much more of an obstacle to surface travel than the mountain ranges since they can be crossed only by very long and expensive bridges, and they expand and contract so rapidly that no bridge lasts very long Hence most travel is by air Few permanent rivers or bodies of standing water #re present on Arrakis and drainage systems are poorly developed even after the ecological transformation completed by Leto II. Flash floods occur occasionally in mountainous areas, hut all m all Arrakis is still quite water poor. Water ice is present in the polar caps, as is the case with all Neta-2C planets, but the total amount is small compared to that of other planets of the group. ARRAKIS, GEOLOGY 35 ARRAKIS GEOLOGY Garres are plentiful, and are easily distinguished by their flat tops They are the oldest exposed areas on the planet, being remains of ancient plateaus formed by widespread lava flow very early m the planet's evolution when water was plentiful and water erosion dominant Ancient water courses are still visible on their tops and their sides One of the most interesting aspects of Arrakeen surface rnotphology is that the mountain chains and grabens run either north-south or east-west (geographic coordinates) This geometry is noted on a number of Neta-2C planets but never as clearly defined as on Arrakis As will be seen shortly, this geometry is intimately connected with the nature of tectonic processes on the planet The small polar caps lie below bled level This "polar sink" is uncommon but geological evidence has shown that the ice caps were much more massive in the distant past even existing as such during the early periods of human habitation (Hackelrhued) Periodic episodes of ice advance occurred with massive glaciers and continental glaciation from the north polar cap extending as far south as 62 N latitude while that from the southern cap had furthest advance to 58 S These massive ice movements from the poles scoured much of the rock in the polar areas, earned it to more temperate climes where the ice melted and deposited its mix of rock flour The polar sinks were thus created Since the present ice caps exist in depressions it has been suggested that energy from Canopus be focused with large solar satellite arrays to form polar lakes The water from these lakes would then be drained through tunnels to provide irrigation to those areas of Arrakis most m need of the water Ghrahc has provided compelling arguments against such a project, concluding that the present climatic balance on the planet would be seriously disturbed with possibly disastrous results GEOLOGIC HISTORY, TECTONICS Arrakis, as a Neta 2C class planet, evolved after formation much as other planets of the classification The