228 THE ERUPTION OF VESUVIUS IN APRIL, 1906. 



led. Two types are common. Great streams that have spread out 

 rapidly at a high temperature, and consequently in a condition of 

 great fluidity, have a surface broken by very angular scoriaceous 

 blocks. A^Tien, on the contrary, the magma flows slowly, its surface 

 stretches or wrinkles, and finally breaks in places, allowing the mol- 

 ten material to exude. These lavas have a more or less even surface. 

 Their j^rogress is silent, whereas the others advance with a charac- 

 teristic noise produced by collisions of the blocks. 



The great flows of 1906 belong essentially to the first type. When 

 I visited Boscotrecase, six days after the eruption, there were no 

 observations possible upon the progress of the lava. It Avas still 

 incandescent in places, however, and till April 24 it was possible to 

 find cavities at the bottom of which glow^ed red-hot lava. 



My observations of 1905 have been most valuable in permitting a 

 better comprehension of the details observable in the lava field of 

 Boscotrecase. In the evening of October 3, 1905, guided by Mat- 

 teucci. I climbed to a point where lava w^as issuing from a tunnel a 

 short distance below the fissure. The opening was hardly more than 

 a square meter in diameter. The incandescent magma flowed rap- 

 idl}', with a velocity of 6 meters a minute. It formed a straight 

 torrent upon the steep slope of the cone. For the first 25 meters the 

 surface was stretched in the direction of the flow. The fluidity w^as 

 such that the lava was easily pierced by a stick, but great blocks of 

 rock thrown upon this moving mass did not sink into it. They simply 

 became fastened to the surface, firmly enough to maintain their posi- 

 tion on the steep slope as they were carried away by the current. 

 Beyond the first 25 meters solidified fragments began to appear on 

 the surface, especially along the edges, where they formed a moraine. 

 This increased rapidly in thickness and encroached upon the central 

 part of the stream, which, at 100 meters from the source, was entirely 

 covered with incandescent fragments. 



The lava flowed continuously, without disturbance or effort, but 

 at one moment we saw^ coming from the mouth of the opening a 

 great fragment which emerged half way and then, caught by the cur- 

 rent, plunged afresh into the moving magma, leaving behind it a 

 swelling, which soon lost its circular shape by merging into the 

 longitudinally striated surface of the surrounding lava. This block 

 formed a large inclusion or pseudo-bomb. 



At the base the flow became a fiery lake. It was an inspiring 

 spectacle. From the incandescent torrent and the Strombolian ejec- 

 tions sheaves of a vivid red vaulted far above us, illuminating the 

 darkness of the night, while at our feet in the distance glowed like 

 small white stars the electric lights of Najiles. 



The surface of another flow studied b}^ me, from a position as 

 near as the radiation of heat would permit, exhibited a constant 



