In 2016 a large ice deposit has been found within the Utopia Planitia region on Mars by the SHARAD instrument on board of the Mars Reconnaissance Orbiter.
The thickness of the deposit ranges from 80 to 170 meters with a composition that's 50 to 85 % water ice, mixed with dust and rocky particles.
It is shielded from the atmosphere by a soil covering estimated to be about 1 to 10 meters thick.

The volume of the ice in the deposit is estimated to be about 14,300 cubic km, so the mass will be about 14 teratons, the mass of the atmosphere of Mars being 25 teratons.

Now, if bulldozers could remove the soil covering in summertime, at daytime the ice would sublimate into the atmosphere and the water vapour would be spread out by the winds.
Of course, at night the vapour would have deposited on the surface again, and when all the ice of the deposit could be spread out evenly in this way about the whole planet, its thickness would be about 10 cm. In practice however it's likely that the various winds will gather the ice at certain places.

The atmosphere of Mars is quite dusty, containing particulates about 0.0015 mm in diameter which give the Martian sky a tawny color when seen from the surface.

Question: if so much water ice could have been spread out on the surface of Mars by uncovering the ice deposit, would that not cover a large portion of the regolith and could not the water vapour in the air at daytime in the summer eventually "wash out" much of the dust in the atmosphere?

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    $\begingroup$ @Conelisinspace check out some of the material discussed in Terrestrial Exoplanet Skies – I've Built a Visual Sky Chart. Is it Accurate? $\endgroup$ – uhoh Oct 19 '18 at 10:46
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    $\begingroup$ Background information for the uninitiated, Earth's blue sky appears blue due to Rayleigh scattering off of statistical fluctuation the number of molecules over lengths similar to a wavelength of light, see also this hyperphysics article [Blue Sky ](hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html). The OP nicely points out that Mars' sky isn't also blue because of the extra stuff in the atmosphere, but I'm not sure if it's because the stuff is red, or because it back-scatters red light from the planet's surface. $\endgroup$ – uhoh Oct 19 '18 at 10:59
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    $\begingroup$ It will not be that bright certainly, but $\lambda^{-4}$ is $\lambda^{-4}$ and so I'm guessing the shape of the spectrum in visible light (i.e. hue) wouldn't change much. It would have to be even lower density (near the surface) before the individual molecules were so far apart on average that it reached wavelength-scale. At that point the sky would be so dim that (I'm guessing) you wouldn't be able to perceive its hue anyway. $\endgroup$ – uhoh Oct 19 '18 at 12:22
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    $\begingroup$ A few issues: (1) dust is raised when dry fine regolith is moved, either by something moving over the regolith, such as a vehicle, or the wind blows the fines of the regolith. (2) would permanently wetting the surface of Mars create issues for people & vehicles moving over the surface of Mars. (3) wind can dry the soil (4) Mars is cold, it only reaches a high temp of about 20C for short periods, would the atmosphere absorb water vapor in useful amounts? (5) will the thin atmosphere of Mars be problematic? (6) over time will the water be lost, like the oceans Mars once had? $\endgroup$ – Fred Oct 19 '18 at 14:04
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    $\begingroup$ On Earth, we have large oceans and big lakes and rivers, humid areas covered with green plants, but also dry deserts with dust storms. Dust from the Sahara is transported by wind from Africa to Europe. I don't believe that the water from ice deposits would spread evenly on Mars. $\endgroup$ – Uwe Oct 20 '18 at 21:10

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