A report to be given at the 34th Lunar and Planetary Science Conference in March shows experimentally that geysers of H2O can occur under Mars conditions and lead to channels cut in slopes on Mars:

MARTIAN GULLIES AND THE STABILITY OF WATER IN THE MARTIAN ENVIRONMENT.
J.Thompson1, D.W.G. Sears2, P.H. Benoit2, and M.S. Kareev2. (1) Arkansas-Oklahoma Center for Space and Planetary
Sciences, Dept. Physics, Univ. Arkansas, Fayetteville, Arkansas 72701. (2) Arkansas-Oklahoma Center for
Space and Planetary Sciences, Dept. Chemistry and Biochemistry, Univ. Arkansas, Fayetteville, Arkansas 72701
"While monitoring the surface of the mixture during reduction in atmospheric pressure, we noted the formation of surface features on the scale of centimeters, notably geysers which appeared suddenly and decreased
in activity over time. The most prominent and abundant surface features were formed between the water volume percentages of 15%-25%. Less prominent
features were also formed in mixtures with a water volume percentage of 30% and 35%."
...
"We find that liquid water, or even ice, if existing in small quantities at near surface levels can be a primary agent in the formation of surface feature formations.
"The intermediate water volume percentages that produced the most numerous surface features are similar to
those suggested for shallow regolith aquifers by Odyssey."
http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1035.pdf

This confirms an earlier report that reached the same conclusion:

Martian Outflow Channel Formation by Water Erosion Under
Nonequilibrium Conditions.
Abstracts of the Lunar and Planetary Science Conference, volume 20,
page 666, (1989).
"An experimental study was carried out in a 2.4m by 4.9m cylindrical
vacuum chamber in order to investigate the possibility that martian
outflow channels were formed by the melting of ground ice. Frozen
soils that were subjected to an increased geothermal gradient at
temperatures about 273K and at an average pressure of 8.38 mbar,
melted and formed water-filled depressions and outflow channels. The
depressions formed as a subsurface ice layer thawed. Water initially
appeared at the surface either during gradual collapse of the surface
material or as geysers. The mode of appearance of water at the surface
was a function primarily of the strength of the ice and the
temperature of the water vapor."
http://adsabs.harvard.edu/cgi-bin/bib_query?1989LPI....20..666M

Bob Clark