"CRATERS OF THE MOON" STEARNS 311 



There are three distinct types of cones in the area — cinder, spatter, 

 and lava cones. The cinder cones, with black, loose, cindery surfaces 

 and smooth conical profiles, are the heaps of lava froth or spray 

 formed at the time of eruptions. Big Cinder Butte is the finest 

 example in the area. Spatter cones are formed when the clots of 

 lava hurled out were insufficiently inflated with gas to form cinders 

 and moved so slowly and for so short a distance that they fell as 

 clots in a viscous state and adhered to each other, building up 

 rather steep-sided cones of small height and diameter. The line of 

 spatter cones southeast of the end of the motor road, all less than 50 

 feet high and 100 feet in diameter, is one of the most perfect in the 

 world. The third type of cone found in the Craters of the Moon 

 is the lava cone or dome. Lava domes consist entirely of lava and 

 are broad and flat, and sometimes surmounted by tiny spatter cones 

 less than 10 feet high. These inconspicuous domes are formed by 

 the quiet and continuous welling out of pahoehoe lava, and as most 

 of the lava escapes through tubes the cones are not high, often only 

 30 to 50 feet. Owl Cavern, Indian Tunnel, and Surprise Cave mark 

 sites of lava domes. 



A curious feature found in the monument are the lava bombs 

 scattered on the cinder and spatter cones. These bombs vary in 

 length from one-half inch to over 13 feet, and in diameter from one- 

 fourth inch to 3 feet. There are three types — spindle, ribbon, and 

 bread-crust bombs. Spindle bombs, which have earlike projections 

 on the ends of a football shaped body, were clots of lava which 

 were hurled through the air with a rotational inotion. The best 

 formed bombs are found close to their source. The ribbon bombs 

 are the long tapering twisted ears that project 3 to 10 inches from 

 the ends of the spindle bomb. These long thin strips of lava were 

 broken otf by the fall of the projectile and lie scattered on the sur- 

 face. Some were formed by the pulling apart of two clots of lava 

 traveling at slightly different speeds or in slightly different direc- 

 tions. The long ribbon bombs, 2 to 13 feet in length and a few 

 inches wide, seem to have originated in one of two ways. A few are 

 lava clots that fell on the side of a cone, ran down the slope while 

 still molten, and were later detached by weathering, and the removal 

 of the adjacent cinders. Other ribbon bombs are formed by the 

 throwing out from a spatter or cinder cone of a large clot of very 

 liquid lava that stretches out during its flight and falls on cinders 

 sufficiently loose to prevent its breaking. A third kind of bombs are 

 light and porous and covered with a skin resembling bread crust. 

 They are formed by a clot of lava filled with gas being hurled 

 through the air. During its flight the crust cools, and as the gases 

 expand the hard skin is cracked open in numerous places. 



