A review of lava flow processes related to the formation of lunar sinuous rilles

Abstract

Abstract. This paper reviews processes which, it is argued, occurred in lunar lava flows and were involved in the formation of lunar sinuous rifles.The development of ideas relating to rille formation is described and evidence which suggests that they are products of lava effusions is outlined.An analytical lava flow model is described which relates the shapes of lava flows to conditions at the commencement of the flows. An essential part of the model is its use of the yield strength of lava as a parameter. It is shown that the model predicts the occurrence of the channel/levee morphology of lava flows.It is argued that the channels of large flows were deepened by melting. Heat transfer processes within lava flows are discussed and analysed and it is shown that a prolonged period of flow is required before melting of the substrate begins. Estimates are given of initial heating periods and subsequent melting rates.The possibility of the occurrence of turbulent lava flow is discussed. Application of the flow model to sinuous rilles and tlows in Mare Imbrium shows that both types of feature could be the remnants of similar effusive events in which the flow could have become turbulent. Turbulent flow is shown to promote erosive melting and it is suggested that the sinuous rilles were cut by the flows which became turbulent.A process of rille formation is described which is consistent with the foregoing arguments and with observations made at Hadley Rille. It is concluded that rilles were formed by the rapid effusion of large volumes of low yield strength lavas.

Estimation of volcanic eruption conditions for a large flank event on Elysium Mons, Mars

“…Unfortunately, the only way of estimating the thickness of the precursor flow itself involves assumptions about the volume eruption rate and rheological properties of the lava. We therefore begin by assuming a We next evaluate the heat fluxes from the lava to the substrate due to viscous dissipation G and conduction through the laminar boundary layer in contact with the ground C. These are given by Hulme [1982]:…”

“…Using the MOLA data, the slopes for the various channel segments are estimated to be 8.5 ø for the proximal "old" part of the channel, 10.0 ø for the vent area, 8.9 ø for the main part of the channel, and 7.1 o for the distributed channel. The concept that a long-lived, high effusion rate volcanic eruption could create an incised channel, rather than a conventional lava flow, was developed to explain the presence of the meandering channels called sinuous rilles on the Moon which must have been formed in the complete absence of water [Hulme, 1973[Hulme, , 1982Cart, 1974]. The volcanic mechanism involves the transfer of enough heat into the surface beneath the lava to raise its temperature to the point where purely thermal erosion (as assumed by Hulme [1973] Fagents and Greeley, 2001] emphasizes that the erosion process is most pronounced when the lava effusion rate and temperature are high, the lava viscosity is low, and the ground over which the initial flow moves is steep and has low mechanical strength.…”

Numerical modelling of sedimentary structures in rivers on Earth and Titan

“…Me an der ing chan nels could also be a re sult of lava flow, e.g. on the Moon (Hulme, 1973). Therefore, we be lieve that our in ves ti ga tions could have some value not only for un der stand ing pro cesses on Ti tan but also for general knowl edge of flu vial pro cesses.…”

The nature and origin of Venusian canali

“…Among these features are meandering channels or canali which range up to -6800 km in length. These channels occur mainly on the planitia and are similar in some respects to lunar sinuous rilles, which are widely believed to have been produced by very low viscosity, high Fe-Ti-rich basaltic lava flows [Hulme, 1973].…”

“…The residual, unmelted material may be transported by the fluid and deposited downstream within the channel (leading to braiding) or as levees and other types of overbank deposits. Essential requirements of this process are that the lava contain sufficient heat to raise the temperature of the substrate to that of its solidus, and that flow be turbulent [Hulme, 1982]. The latter condition is also necessary in order to permit transport of residual, unmelted material.…”