VOLCANO OF MATAVANU IN SAVA If. 
Yol. 66.] 
329 
Places are common where the surface is covered with fresh sheets 
of lava measuring an inch or even less in thickness ; and the surface 
is honeycombed with channels along which the lava has flowed, 
channels which are occasionally deep and open, but often have a 
crust, sometimes thick, sometimes so thin as to give way under a 
man's weight, and form dangerous pitfalls for the unwary. There 
are, too, caves and bubbles of all sizes up to many feet in diameter, 
often also covered with only a thin roof equally liable to collapse 
(PI. XLTX, fig. 1), and many areas, sometimes extensive, where the 
liquid lava beneath has found a vent lower down after a crust has 
formed on the surface, and the whole crust has subsided after the 
manner of the plain of Thingvalla. Tunnels can be seen by which 
the lava has escaped. 1 
This class of subsidence by lava flowing out from under a crust 
seemed to me common on the lower parts of the lava as well as on 
the upper, and there are two notable examples at the eastern foot 
of the cone (PI. XLV, fig. 2). The lava-tunnels and evidences of 
rapid flow, superficial and deep, are numerous along the line of great 
fumaroles. On my ascent of the cone I had occasion to cross the 
line three times, in order to find a practicable route. From the causes 
named above, the surface, especially in the upper part, was so rotten 
that progress was extremely difficult; while the certainty that the 
river of molten lava was running somewhere below at an uncertain 
depth and under a crust of unknown thickness, combined with the 
approach of night, rendered delay undesirable. I was, therefore, 
unable to examine the fumaroles carefully 2 ; but, so far as I could 
see, one of them was a large hollow with precipitous sides, 
apparently of the nature of a subsidence from the collapse of a 
crust of lava by combined remelting and withdrawal of fluid 
support below ; and subsequent examination of similar places near 
Kilauea has confirmed this opinion. At Matavanu few of them 
appear to have been examined, and in still fewer was the liquid 
lava visible, but I understood that in one it had been seen flowing 
at a depth of 30 to 40 feet. 3 
The slope of these lava-fields is very gradual. The distance of 
the crater from the sea is about 7 miles as the crow flies ; but, 
following the sinuosities of the underground current, it may be 
estimated as somewhat over 10 miles. If the foot of the cone be 
taken at a height of 1800 feet, this gives an average fall of one in 
30, or about 6°, a slope which is of the same order of magnitude as 
that of many of the Icelandic streams. The slopes of some of the 
Hawaiian volcanoes formed of the same class of lava are stated by 
1 Compare T. Anderson ‘ Volcanic Studies’ 1902, pis. Iviii—Iviii A &lxxii. 
2 The next day the wind blew the fumes against us, and prevented further 
examination. 
3 I have since received from Mr. Barts of Fagaraalo a photograph of one 
such 4 pit crater,’ showing precipitous walls composed of very numerous thin 
layers of lava, presumably both surface-flows and intrusive sheets, comparable 
to those in the wall of the crater; also another photograph showing a pit with 
its walls coated with lava frozen on to them, somewhat like the wall of the 
crater shown in PI. XLVII. This pit appears to lune been an orifice by 
which lava rose and flooded the surrounding lava-field. 
