692 



THE NATIONAL GEOGRAPHIC MAGAZINE 



COLLAPSED MUD VOLCANO — A CALDERA IN MINIATURE — NEAR VOLCANO LAKE, 

 MEXICO, 40 MILES SOUTH OF THE INTERNATIONAL BOUNDARY LINE 



they in the featureless silt plain which 

 constitutes most of the desert surface. 

 The best known of these groups is now 

 submerged by the Salton Sea. Its situ- 

 ation is about 6 miles south of the station 

 of Old Beach, the junction point for the 

 Imperial and Gulf branch of the South- 

 ern Pacific Railroad. ' These solfataras, 

 before their submergence, were dis- 

 tributed in two or three sub-groups, near 

 some mounds of volcanic rock which rise 

 above the desert floor. They have been 

 visited at various times by explorers and 

 during at least one of these visits a 

 tragedy was narrowly averted. The ex- 

 plorer, in attempting to cross the thin 

 crust that covers the hot mud bog which 

 separated the mounds from the solid 

 ground around them, broke through the 

 crust and was so scalded that his explo- 

 rations had to be given up and his life 

 even was for a time in jeopardy. 



The craterlets of mud look more like 

 irregular beehives in various stages of 

 dilapidation than like any other familiar 

 form which might be mentioned (see 



page 698). In the tops of these mounds 

 there are often cup-shaped depressions, 

 and from these or from vents in the sides 

 steam and other gases are constantly 

 rising (see page 699). These gases con- 

 tain much sulphurous vapor, and this 

 vapor, condensing as it reaches the air, 

 lines the vents with brilliant yellow crys- 

 tals and powders the adjacent surface 

 with a golden dust that gives curious 

 and even attractive effects. Round about 

 the mounds are pools of hot mud or 

 water, the latter often so acid that shoes 

 or wearing apparel moistened with it are 

 destroyed. 



The second important group of solfa- 

 taras lies not in California, but about 40 

 miles south of the international boundary 

 in Mexico, along the western shore of 

 A r olcano Lake and near the base of a 

 dark butte called Cerro Prieto. The vol- 

 canoes here cover many acres (see pages 

 698 and 699) and are much more active 

 than those on the American side of the 

 line. Many of them are boiling and bub- 

 bling continually, emitting weird muffled 



