RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 113 



i 



FIG. 109. Surface of lava of the Pahoehoe type. 



The surface which flowing lava assumes, while subject to con- 

 siderable variation, may yet be classified into two rather distinct 

 types. On the one hand there is the billowy surface in which 

 ellipsoidal or kidney-shaped masses, each with dimensions of from 

 one to several feet, lie merged 

 in one another, not unlike ah 

 irregular collection of sofa 

 pillows. This type of lava has 

 become known as the Pahoehoe, 

 from the Hawaiian occurrence 

 (Fig. 109). A variation from 

 this type is the " corded " or 

 " ropy " lava, the surface of 

 which much resembles rope as 

 it is coiled along the deck of 

 a vessel, the coils being here the 

 lines of scum or scoriae arranged 

 in this manner by the currents 

 at the surface of the stream 

 (Fig. 123, p. 124). A quite 

 different type is the block lava 

 (Aa type) which usually has a 

 ragged scoriaceous surface and 

 consists of more or less separate 

 fragments of cooled lava (Fig. 



131, p. 130). 

 i 



FIG. 110. Three successive views to 

 illustrate the growth of the Island of 

 Savaii from the outflow of lava at 

 Matavanu in the year 1906. a, near the 

 beginning of the outflow ; b, some weeks 

 later than a ; c, some weeks later than 

 6 (after H. I. Jensen). 



