PEALE.l 



THEEMAL SPRINGS AND GEYSERS OF ICELAND. 



307 



feet is the most common measurement.* When the geyser is not in 

 action the water over the tube in the center of the basin is in constant 

 motion, the hot water rising from the tube constantly displacing the 

 cold water, as proved by Paijkull, who threw bits of paper into the basin 

 and thus indicated that the water after rising was driven slowly towards 

 the edges, when it sank and flowed back along the bottom of the basin. 

 From this one would naturally expect to find the temperature in the 

 basin a shifting one, not only as regards the different parts of the basin, 

 but also as regards the times of observation when compared with the 

 times of eruptions, and such is found to be the case when the different 

 temperature observations are compared. This accounts also for the dif- 

 ferences between different observers. The steam from the geyser has 

 a slight odor of sulphureted hydrogen, and the water also has a slight 

 taste of the same gas, but it soon passes off. 



There are two kinds of eruption in the Great Geyser (in which respect 

 it resembles a number of our own geysers, especially the Union in the 

 Shoshone Basin, and the Castle and Giant in the upper basin of Fire- 

 Hole Eiver). After the minor eruptions the water does not sink, 

 although they are preceded by the same subterranean explosions as the 

 great eruptions. 



According to Descloizeaux, detonations, accompanied with upliftings 

 of two or three feet, occur regularly every hour and a half to two hours, 

 becoming stronger and more frequent as an eruption is approached. 

 Bunsen calls these upheavals "conical water hills." The eruption con- 

 sists of a succession of jets following each other at short intervals, each 

 consecutive jet attaining a greater height than the previous one, until 

 the maximum is attained at the end. The column is fountain-shaped 

 at the top. After the eruption is over, the water disappears from the 

 basin and sinks about 10 feet in the tube, and does not resume its old 

 level for from two to seven hours. 



As to the interval between the eruptions the data are mea'ger. The 

 following table gives the different observations : 



Authority. 



Date. 



Interval or period of 

 eruptions. 





Middle of aeventeentli century 



Middle of eighteenth century 



1804 









Oblsen 



Every 6 hours. 

 > Once in 30 hours. 





1809 





1810 





1814 







181C 





KiTifi Von Nidda 



1833 



24 to 30 hours. 





1846 



11 to 30 hours. 





1872 



Every 6 hours. 







From this it would appear that the most common interval is about 

 thirty hours. According to Paijkull, the natives state that weeks often 

 elapse between eruptions, and sometimes several eruptions will occur 

 in one day. 



* Mr. John Coles, loccit, p. 23, who visited thegoyser in 1881, says tlie cone rises 12 

 feet above the surrounding level, and measures 101 by 75 yards at the base, and that the 

 basin on the summit measures 5H by 49 feet. In "Frost and Fire" a sectioti of the 

 Great Geyser shows that at a depth of 45 feet there is a ledge from beneath whieh the 

 stream ajipears to come. 



