ORIGIN OF LAKE BASINS. 19 



At Ice Spring biittes, a group of small volcanic craters, near Fillmore, 

 Utah, there is a pool of water in the throat of an extinct volcano, which 

 occupies a depression formed by the recession of the lava that once rose in 

 and partially filled the crater.^ 



The Soda ponds on the Carson desert, near Ragtown, Nevada, occupy 

 lapilli craters, the rims of which rise 20 to 80 feet above the surface of 

 the adjacent plain. The larger pond has an area of 268 acres and a 

 depth of 147 feet, and its surface is 60 feet below the general level of 

 the desert .- 



A crater similar in character to those holding the Soda ponds, occurs 

 on one of the islands in ]\Iono lake, California, and is oc-cupied by alkaline 

 waters. The water within the crater stands at the same level as the sur- 

 face of the surrounding lake, a connection between the two being main- 

 tained by percolation through the intervening embankment of incoherent 

 lapilli.3 



One of the numerous craters near San Francisco peak, Arizona, is said 

 to hold a lake at a considerable altitude above the adjacent country. In 

 the summit of ]Mt. Toulca, Mexico, a deep depression produced by violent 

 eruptions is stated by Davis to have been similarly transformed. 



In many volcanic regions in other countries, lakes of this class are 

 known to occur. They are common in Italy, on North Island, New 

 Zealand, and are reported to occur in the Caucasus, on the Solomon 

 Islands, in India, etc. A typical example of a water-filled crater is fur- 

 nislied by Laacher See, on the border of the Eifel, Germany, and has been 

 described and illustrated by Edward Hull.* 



Still another class of lakes due to volcanic agencies occur where the 

 summits of volcanoes have been blown away by the energy of the con- 

 fined vapors within ; or when the base of a volcanic pile has been melted 

 so as to cause it to suljside into the conduit from which the material com- 

 posing the mountain was extruded. 



It is believed that basins have resulted from each of these processes, 

 but observations on their actual formation are lacking. It is known, 

 however, that volcanic mountains of large size are sometimes literally 

 blown away, as happened in the case of Krakatoa, in 1886. 



1 G. K. Gilbert. " Lake Bonneville." V. S. Geol. Surv., Mono^napli No. 1, 1800, p. ".22. 



2 I. C. Kussell. "Lake Lahontan." U. S. Geol. Snrv., Monograph No. 11, 1885, pp. 

 72-80. 



* I. C. Ku.ssell. "Quarternary History of Mono Valley, California." U. S. Geol. Surv., 

 8th Ann. Rep., 188(5-87, p. 87:}. 



* " Volcanoes : Past and Present." Contemporary Science Series, pp. 122-123. 



