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Degrees of Valley Whiteness - wbdeford - 2021-12-16
There is a discussion elsewhere about the effect of flooding on the color of the valley. It has been my experience that after the valley dries from a flood, it is much whiter than before, while others are saying it is often browner after the flood.
Anyone with light to shed on this?
RE: Degrees of Valley Whiteness - DVexile - 2021-12-17
It depends on how long after the flood and whether the water table below the surface eventually stops providing water to the surface by capillary action.
Flooding events tend to both dissolve white surface minerals as well as deposit sediment so initially after the flood the surface is just a dirty brown as most of the water is absorbed into the soil rather than immediately evaporating. The flood basically washes the white surface from the top with the minerals being absorbed into the top soil layers. So on that short time scale flooding events make the surface less white.
Over time capillary action brings high salinity water to the surface where it evaporates leaving white minerals behind and thus the surface whitens over time. Thus during this stage the longer in time from the flood the whiter the surface.
Eventually however the soil desiccates enough that the water table is too low for capillary action to continue to bring mineral laden water to the surface and evaporate. At this point wind takes away white minerals and deposits brown minerals and without the capillary action to continuously replenish the surface with white mineral the surface becomes brown over time. So at this stage the more time since the flood the less white the surface.
Section 2.2 on page 5 of the article linked below gives good photos and explanation of the process on a different salt pan:
https://mdpi-res.com/d_attachment/remotesensing/remotesensing-12-00474/article_deploy/remotesensing-12-00474.pdf
BTW, I learned much of this first hand the hard way some 20 years ago when I made the mistake in Saline Valley of thinking it would be safest to walk on the whitest part of the pan. No indeed, a really white pan means there is quite a bit of water under it keeping the surface nice and white with capillary action. Feet punched through into some of the grossest mud I’ve ever encountered…
RE: Degrees of Valley Whiteness - GowerGulch42 - 2021-12-18
Confirm and concur. The salt flats are generally whitest just before the first big rains of monsoon or winter.
RE: Degrees of Valley Whiteness - wbdeford - 2021-12-18
Great stuff!!...thanks for the detailed explanation
Attached is how I came to my hypothesis that flooding makes it whiter. The middle 2010s were very dry, at least in the winters, and I noticed the valley getting browner and browner. It was very brown when I was out there in April 2015. Then, came the storm in October 2015, after which I visited in November and found it whiter than I have ever seen it. By April 2016, it was still very white. I attributed this to the flood and still am having trouble seeing any other explanation for it.
The four satellite images in the attached are:
1) Before the flood
2) Still flooded
3) Dried surface
4) A few months later.