[Proc. Roy. Soc. Victoria, 32' (N.S.), Pt, I., 1920.;, " 



Art. XX. — Notes on Dust Whirls in Sub-Arid Western 



Australia. 



By J. T. JUTSON 



((Formerly a Senior Field Geologist, Geological Survey of Western Australia; 

 late Acting Lecturer in Geology, University of Western Australia), 



[Bead December 11th, 1919.] 



Introduction. 



t 



Dust whirls are well known plienomena in arid and sub-arid 

 Kjountries. Tliey are ascending spiral air currents, which also 

 move in a linear direction, and which carry varying amounts of 

 •dust and fine sand with them. 



Dust Avhirls have been well described by W. M. Davis^ and by 

 E. E. Free. 2 Davis points out^ that an inflow of air is begun 

 towards the place of ascent, but as the various inflowing currents 

 •move for too shol-t a distance to be systematically influenced by 

 the earth's rotation, and as their irregular flow does not allow 

 them to meet precisely at a centre, they turn a little to one side 

 •or the other,, according as the stronger inflow decides, and a little 

 w^hirl is then developed rotating indifferently one way or the 

 -other. Free also states^ that the rotation seems to be indiscrimin- 

 .ately clockwise, or contra-clockwise, as frequently one as the other. 



Dust whirls are recognised to be due to overheating of particular 

 portions of the land surface, with the result that equilibrium is 

 •disturbed, and the air rushes upwards. The surrounding air then 

 ilows inwards, and a whirl is caused. 5 



Dust whirls liave been recorded from various countries, and a 

 valuable list of the literature has been given by Free in tlie work 

 .already cited. 



Dust whirls may reach a considerable height. Thus Davis^ 

 .states they may reach a height of several hundred, or even a tliou- 



1. " Elementary Meteorology," 1894 p. 201. 



2. U.S. Department of Agriculture, Bureau of Soils, Bulletin No. 68, 

 1911, p. 38, et. seq. 



3. Loc. cit. 



4. L.OC. cit. 



5. See Free, loc. cit. 

 <6. L.OC. cit. 



