332 T. A. Jaggar — Conditions affecting Geyser Eruption. 



escape at the surface during the intervals between eruptions, 

 were less numerous, very small, and slower in their upward 

 movement through the soapy solution ; after five or six erup- 

 tions it became evident that the intervals were somewhat 

 shorter (averaging 1 min. 20-30 seconds instead of 1 min. 30-40 

 seconds) and the periods very noticeably longer (40-45 seconds 

 instead of 20 seconds). The ebullition in the flask was 

 more violent than in the case of pure water, and columns 

 of fine bubbles accumulated in the geyser-tube, only to be 

 ejected with a violent sputter and give place to a new accumu- 

 lation. It was evident that these accumulated myriads of tiny 

 steam bubbles, confined within the tube and adhering to the 

 walls of the tube, formed a cushion opposing considerable 

 resistance to pressure from below. 



After the diffusion of the soapy solution had become general, 

 the reservoir (and consequently the geyser-column) was lowered 

 to the level a ; the intervals were at once shortened to an aver- 

 age of about one minute, in consequence of the rapid accumu- 

 lation at the surface of the column and within the tube of the 

 cushion of steam bubbles. So resistant is this cushion, that as 

 it grows by the addition of new bubbles rising from below, the 

 water column is actually depressed, down to the neck of the 

 flask ; here a point is reached where the f rictional resistance of 

 the froth cushion and the hydrostatic pressure are balanced. 

 A further accumulation of steam forces up the column of 

 foam, release of pressure permits the water to burst into vio- 

 lent ebullition and an eruption takes place. From this it 

 would appear that in those geysers where the tube is small, the 

 growth of a cushion of steam soap-bubbles may play a very 

 important part in accelerating the development of eruptive 

 conditions. 



Summary. 



1. Geysers and boiling springs are subject to the laws of 

 hydrostatic pressure, in common with other springs. 



2. In a geyser-spring, overflow once established may be main- 

 tained by convection even against a reversed head ; this leads 

 to a critical point in the spring's mode of discharge. 



3. In this condition, with a constant source of heat, very 

 slight changes in the local head are sufficient to induce a change 

 in the nature of a geyser-spring's mode of action. Such change 

 in the head may be caused by variation in rainfall, by building 

 up a sinter cone, by forcing new outlets at lower levels, or by 

 clogging of old conduits. 



4. Geyser basins afford drainage channels for meteoric 

 waters. The drainage takes place by either continuous over- 



