within the range of the amazing disaster. So powerfully was this water
driven from the crater that the districts immediately at the base of
the cone were in a manner overshot by the vast stream, and escaped
with relatively little injury.

When it comes forth from the base of the cinder cone, or from one of
the small peripheral craters, the lava stream usually appears to be
white hot, and to flow with almost the ease of water. It does not
really have that measure of fluidity; its condition is rather that of
thin paste; but the great weight of the material--near two and a half
times that of water--causes the movement down the slope to be speedy.
The central portion of the lava stream long retains its high
temperature; but the surface, cooling, is first converted into a tough
sheet, which, though it may bend, can hardly be said to flow. Further
hardening converts these outlying portions of the current into hard,
glassy stone, which is broken into fragments in a way resembling the
ice on the surface of a river. It thus comes about that the advancing
front of the lava stream becomes covered, and its motion hindered by
the frozen rock, until the rate of ongoing may not exceed a few feet
an hour, and the appearance is that of a heap of stone slowly rolling
down a slope. Now and then a crevice is formed, through which a thin
stream of liquid lava pours forth, but the material, having already
parted with much of its heat, rapidly cools, and in turn becomes
covered with the coating of frozen fragments. In this state of the
stream the lava flow stands on all sides high above the slope which it
is traversing; it is, in fact, walled in by its own solidified parts,
though it is urged forward by the contribution which continues to flow
in the under arches. In this state of the movement trifling accidents,
or even human interference, may direct the current this way or that.