Natural Hazards: Causes and Effects - Disaster Management Center ...

Success in diverting lava flows by bombing depends on several factors. Bombing may be
ineffective until the flow has developed a well-established feeding tube, a channel confined
between levees at a level above its surroundings, or a lava pool confined at a high level in a
thin-walled cone. Even when one or more of these conditions exists, there must also be good
visibility to permit selection of the best targets and accurate bombing. Very commonly, during
eruptions visibility from the air is poor because of volcanic fume, smoke from burning
vegetation, and ordinary clouds. Even if bombing can be accomplished, the successful
diversion of the flow is dependent on favorable topography. If a flow is in a valley appreciably
deeper than the flow is thick, there is no hope of directing the diverted lava out of the valley.
The new lava stream will simply follow the margin of the old one, and it may actually flood over
the old one and rejoin its feeding river downslope.
Although there does appear to be a considerable possibility of diverting fluid basaltic lava flows
by bombing where conditions are favorable, it is not at all certain that the method would work on
the more viscous block lava flows.
Diversion of lava flows from important areas may also be accomplished by means of artificial
walls, designed not to act as dams but to turn the flow through a relatively small angle into a
new course. The possibility depends on the fact that many flows exert a surprisingly small
amount of thrust against objects in their path.
The diversion barriers can be constructed by bulldozers, using loose rock materials readily at
hand, or ripped up from the substrata by the bulldozers. The height of wall that is necessary
depends on the local topography and the size of the lava flow it is to divert.
Still another method of restricting and diverting lava flows has been the subject of half-joking
conjecture for several decades. The idea, finally tried, was simply to spray water from fire
hoses onto the edge of an advancing lava flow to chill it and retard its progress. It was given
some credibility by the behavior of some lava flows on entering the ocean. For instance, when
the 1911 flow of Matavanu, Samoa, entered the ocean it turned and advanced along shore,
instead of continuing straight on into deep water. It seemed possible that the change of course
was caused by chilling of the oceanward side of the flow, making it easier for the lava to spread
laterally. It was also possible that the change was at least partly the result of the lava following
the broad depression between the shoreline and the low ridge at the outer edge of the coral
reef. However, in 1960 at Kilauea the flow behaved in the same way, and there was no
depression parallel to the shoreline to guide it. Later in the 1960 eruption, on several occasions
the Hawaii Fire Department tried spraying the flow margin to determine its effects. One
example may be given. For several days the edge of the flow had been creeping slowly toward
a wooden house. When the lava was about six meters (20 feet) from the house, volunteer
firemen, who were not then otherwise occupied, turned two streams of water from 75 millimeters
(three-inch) hoses onto the side of the flow. Within a few minutes the lava stopped moving, and
it remained stationary for several hours. In short, it was found that even with rather small
amounts of water the spread of the flow could locally be checked for periods long enough to
remove the contents of buildings, or even to move entire buildings to safety.
The use of the spraying method depends, of course, on the availability of large amounts of
water and of suitable pumps and other equipment. Its success depends on favorable
topography and on the volume and rate of flow of the lava. 16