Barriers Against Lava — MACDONALD 
267 
the height of a barrier need not be as great as 
the depth of the lava in order to turn the 
course of the flow. 
The next experience with a barrier came on 
March 13, when fluid pahoehoe flows were 
erupted in cleared land adjacent to the Pahoa- 
Kalapana road. Seizing a favorable oppor- 
tunity, we placed in the path of one of the 
advancing flow tongues a wooden plank about 
8 feet long, 18 inches wide, and 2 inches thick. 
The plank was set on edge in nearly vertical 
position, diagonally to the path of the flow, 
and held in place by a few loose rocks placed 
behind it. The intense heat of the approach- 
ing flow front prevented us from doing a good 
job of blocking the plank in place. The lava 
came in contact with the plank and tilted it 
back to a somewhat flatter angle, but the lava 
was turned to one side by the plank, and in 
spite of the insecure blocking did not push 
the plank aside (Fig. 4). The plank ignited 
and burned slowly, but continued to divert 
the flow for half an hour, until a new tongue 
of lava approached it by a different path and 
buried it. 
On the morning of March 21a tongue of a 
large aa flow entered the head of a small valley 
that led directly to a small plantation camp 
owned by Koji Iwasaki. It was obvious that if 
the lava continued down the valley the camp 
was doomed. In an effort to divert the flow 
across the low ridge south of the valley, a wall 
about 1,000 feet long and averaging about 10 
feet high was hurriedly thrown up by bull- 
dozers (Fig. 5) working under the direction of 
Arthur Lyman of Olaa Sugar Company, with 
the advice of J. P. Eaton of the Hawaiian 
Volcano Observatory staff. During the after- 
noon the flow front reached the barrier, and 
was successfully turned by it. However, after 
the flow front had moved only about 50 feet 
along the barrier the supply of lava was cut 
off, and that tongue of the flow stagnated. 
Later in the eruption another flow tongue 
came against a different part of the barrier. But 
again, after the lava had moved along the bar- 
rier only a few feet, the flow stopped. Still 
later flows swept down the mountainside by 
other routes remote from the barrier and 
destroyed the Iwasaki camp. 
Thus, the Iwasaki barrier was not actually 
subjected to a critical test. However, it does 
supply some valuable data on barrier con- 
struction. The wall was built by 6 bulldozers 
(three D-8’s, two D-7’s, and one TD-14) in 
less than 4 hours, working in an area of old 
pahoehoe flows where loose material avail- 
able for incorporation in the wall was not 
abundant. At times the bulldozers worked 
within a few feet of the advancing flow front 
without trouble, and after the first few min- 
utes without undue worry to the operators. 
Because of the small amount of space avail- 
able, the wall was placed at too flat an angle to 
the course of advance of the flow for best 
results. Nevertheless, the flow front was suc- 
cessfully turned. The flow piled up to nearly 
double the height of the wall, but only a few 
fragments rolled over the wall. 
About noon on March 22, Robert Yamada 
started construction of another series of bar- 
riers to try to divert another portion of the 
flow from his coffee plantation near the coast. 
The work was done by four TD-24 bulldozers 
under the supervision of Yamada’s son, 
Donald. The first barrier was placed at much 
too obtuse an angle to the course of the ad- 
vancing flow. Moreover, the terrain was not 
really favorable to the successful operation of 
diversion barriers. The drainage system is 
poorly defined, and the slope of the land sur- 
face is so low that barriers need to be placed 
at a very acute angle to the course of the flow 
in order to provide sufficient grade in the new 
channel behind the barrier. A plan of the 
Yamada barriers is given in Figure 6. 
At 3:30 p.m. on the same day a tongue of 
the lava flow was advancing down a road 
toward the barrier at a rate of about 60 feet an 
hour, with its front only 260 feet from the 
growing barrier. It became evident to Curtis 
Kamai and me that this tongue would reach 
the barrier before the main body of the flow 
reached it somewhat farther upslope, and 
