Distribution of Sinuous Rilles and Water on the Moon

Abstract

WITH the aid of the Lunar Orbiter IV high resolution photographs, the morphology and distribution of sinuous rilles over a large fraction of the surface of the Moon can be studied in detail. Sinuous rilles often begin in craters although the sources of some are not so easily described. Where relative elevations are obvious, the source always appears to be on higher ground. Channel lengths range to about 10³ km and widths to a few kilometres. Although the widths of individual rilles are rather uniform along their courses, there are some that grow conspicuously narrower toward their termini; for example, Rima Prinz I (Fig. 1). Channel depth generally decreases with distance from the source. Narrower meandering channels are found on the floors of several of the wider rilles. The central channel in Schroeter's Valley (Fig. 1) and the rille in the crater Alfred E. Neuman (Fig. 2) show striking examples of mature meanders with goosenecks and oxbows. Sinuous rilles are sometimes diverted along underlying fractures or around hills (Fig. 1). With the exception of interruptions caused by more recent impact craters they show no discontinuities. A few of the channels exhibit contributory or distributary patterns. Nearly all channels fade imperceptibly into the surrounding plains whereas a few show evidence for deposition of material at their termini. For example, material from the rille emerging from the crater Krieger seems to have been deposited over a wide area that overlies part of an apparently older rille (Fig. 3).