[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 



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

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



[Read December 11th, 1919.] 



Introduction. 



Dust whirls are well known phenomena in arid and sul)-arid 

 'Countries. lliey 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 whirls have been well described by W. M. Davisl and by 

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

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

 move for too short a distance to be systematically influenced by 

 the earth's lotation, 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 

 whirl 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. Tlie surrounding air then 

 flows inwards, and a whirl is caused. ^ 



Dust whirls have been recorded fi-om various countries, and a 

 valuable list of the literature has Ix^en given by Free in the work 

 already cited. 



Dust whirls may reach a considerable height. Thus Davis^ 

 states thev mav reach a height of several hundred, or even a thou- 



1. " Elementary Meteorology," 1S94 p. 201. 



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

 1911, p. 38, et. seq. 



3. Loo. cit. 



4. LiOc. cit. 



5. See Free, loc. cit. 

 «6. L/OC. cit. 



