Blowing Sand

Now lets take a look at what it takes for dirt and sand to start blowing across the land.

Any one who has been to the desert, beaches or dust boll knows it doesn't take much wind to start sand and dust blowing. What the amount or percentage this is with wind speed I have not been able to find measured reference data on yet. The concern is that as more and more sand and dirt gets picked up into the air then the pressure it exerts at any one speed goes up proportional to the weight of a cubic ft of this mix as compared to a cubic ft pure air (density ratio).

During the PS it is likely to have earthquakes of vertical g force greater than one. This means that dirt, sand, and rocks will bounce into the air. If at the same time winds are of sufficient magnitude to catch the dirt then this will begin to move as a dense cloud rapidly across the landscape. I would expect rather dense clouds of blowing dirt and sand to be possible with winds above 160 miles/hr (257 KM/hr) under these conditions. Dirt could be moved great distances and easily completely cover things up. It's just a chance we all will be taking.

As an example: If one assumes its possible for 2% dirt and 2% water blowing with sufficient wind speed to stay airborne then how much additional force does this result in?

Density of air is about .00119 gm/cc (cc=cubic centimeters). With water = 1 gm/cc and sediments (sand-dirt) about = 2 gm/cc. Assume high winds cause a blowing mixture of 2% dirt, 2% water and 96% air. Resulting density is about (.98*.00119)+(.02*1)+(.02*2) = .0612 gm/cc. Since wind force is proportional to density we get .0612/.00119 = 51.4 time more force of pressure than air alone. At this time I can only estimate this to occur around or above 160 Miles/Hr. This would result in a force of 51.4*107.6 = 5530 lb/sq ft (38 lb/sq inch or 2700 gm/sq cm or 27000 KG/sq Meter) for a surface 90 degrees to the wind. This is equivalent of the weight of about two cars for each square foot for a wind of just 160 miles/hr (257 KM/hr). I don't know many structures that will withstand this much force.

Summary: With wind picking up sand, dirt and water (total of 4%) it can easily produce over 51 times the surface pressure, as compared to pure air, at above an estimated 160 Miles/hr (257 KM/hr). At one percent the force is approximately 13 times that of air alone. Wind blowing water and dirt can produce significant forces on anything standing in it's way. With sand, dirt and water in the air even at low percentages of .15 to .2% one can expect double the forces of air alone. This extra force would significantly lower the speed at which things in general become airborne.

Offered by Mike.