Posted by Rebecca Thomas, Department of Physical Sciences, The Open University, UK.
Recent channelized flows from vents in the Cerberus plains of Mars demonstrate the difficulties of uniquely ascribing process to landforms on other planets. The image below shows two fissures emanating from a wrinkle ridge. Both fissures appear to be sources of approximately contemporaneous channels running down onto the surrounding plains (Thomas, 2013). The channel in the west is constructive and differs from that in the east which is clearly shows several phases of incision (Image 1).
On Earth, lava channels tend to be constructive and confined between levees of their own making. In contrast most water flows incise their channels. One potential explanation for the origin of these channels is that the western channel was constructed by lava flowing from a fissure caused by dyke propagation to the surface. The eastern channel may have been incised by an outpouring of water from a breached aquifer. There are other examples of water outflow on Mars have been ascribed to dyke propagation breaching aquifers (e.g. Russell & Head, 2003), so it is reasonable that the two processes could occur at a similar time in the same region.
However, it is not possible to state categorically whether lava or water is responsible for either type of channel. For example, incised channels are seen on volatile-depleted bodies such as the Moon and Mercury (Hurwitz et al. 2012, 2013), where thermal and/or mechanical erosion by very fluid lava is the probable agent (Image 2). Conversely, water-bearing sediment can form constructed channels with marginal levees in an aggradational settings particularly where the sediment fraction is high.
For this example on the Cerberus plains, there is not a clear source for the sediment to form the constructed channel by aggradation, so a volcanic explanation is best-supported. The material which formed the incised channel, however, is open to debate: it must have been a low-viscosity fluid, but data beyond the channel’s planform morphology will be necessary to determine whether this was water or lava.
Hurwitz, D. M., Head, J. W., Wilson, L., and Hiesinger, H. (2012). Origin of lunar sinuous rilles: Modeling effects of gravity, surface slope, and lava composition on erosion rates during the formation of Rima Prinz, J. Geophys. Res. Planets, 117(E3), doi: 10.1029/2011JE004000.[Abstract]
Hurwitz, D. M., J. W. Head, P. K. Byrne, Z. Xiao, S. C. Solomon, M. T. Zuber, D. E. Smith, and G. A. Neumann (2013), Investigating the origin of candidate lava channels on Mercury with MESSENGER data: Theory and observations. J. Geophys. Res. Planets, 118(E3), 471–486,doi: 10.1029/2012JE004103. [Abstract]
Leverington, D.W. (2011). A volcanic origin for the outflow channels of Mars: Key evidence and major implications, Geomorphology, 132, 51-75, doi: 10.1016/j.geomorph.2011.05.022. [Abstract]
Russell, P. S. and Head, J. W. (2003). Elysium-Utopia flows as mega-lahars: A model of dike intrusion, cryosphere cracking, and water-sediment release. J. Geophys. Res. Planets, 108(E6), 5064, doi: 10.1029/2002JE001995. [Abstract]
Thomas, R.J. (2013). Identification of possible recent water/lava source vents in the Cerberus plains: Stratigraphic and crater count age constraints, J. Geophys. Res. Planets, 118(E4),789-802, doi: 10.1002/jgre.20071.