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PACIFIC SCIENCE, Vol. II, October, 1948 
forest growth. The advance of the koa forest 
across more than half a mile of barren surface 
would seem to demand at least 300 years, and 
growth of the tree with a diameter of 7 feet 
would seem to require perhaps 300 years. The 
time lapse between emplacement of the two 
upper lava flows enclosing the Uwekahuna tuff 
could well approach 1,000 years. 
Above the lower outcrops of Uwekahuna 
tuff, truncated by the present crater wall, are 
at least 30 pahoehoe flows ranging in thickness 
from 1 to 35 feet (Macdonald, in press) and 
separated by flow contacts which show no evi¬ 
dence of prolonged erosion or soil accumulation. 
This epoch of rapidly recurring eruptions of 
fluid lava apparently filled the supposed old 
crater, overflowed the old outer rim at least 
one flow deep on the northwest (the tree mold 
flow), and restored a constructional dome shape 
to the summit of Kilauea. Reconstruction of 
the probable shape of the dome by using present 
surface contours in segments that have not been 
faulted, and restoring the measurable amount of 
slump in the down-faulted segments, indicates 
that the probable summit of the dome was 
elongated east-west across the north end of the 
present caldera between Uwekahuna and the 
east end of Kilauea Iki. On Figure 1, the con¬ 
tours of the unfaulted Kilauea surface are indi¬ 
cated by a slightly heavier contour line. 
This epoch of rapidly recurring overflow ap¬ 
parently closed with the collapse of at least 
part of the present caldera and with the start 
of a series of explosive eruptions which de¬ 
posited the members of the Keanakakoi forma¬ 
tion (Wentworth, 1938: 92) on the surface 
of the present caldera rim. 
KEANAKAKOI FORMATION 
The Keanakakoi formation includes all frag¬ 
mental deposits emplaced on the present rim of 
Kilauea by explosive eruption of the summit 
crater. In theory it should represent all of the 
late explosive eruptions, but of necessity any 
explosions too feeble to deposit an appreciable 
layer of material on the rim exclude themselves 
because they have left no visible record. The 
present interpretation identifies deposits from 
21 different explosive eruptions separated by 
breaks representing time lapses to be measured 
at least in years. Not less than seven of these 
breaks were long enough for re-establishment of 
a vegetative cover on the humid windward rim. 
Ten of the eruptions involved only phreatic 
explosions; 11 were magmatic explosions or in¬ 
tense lava fountaining. 
The oldest layer of known pyroclastic material 
on the surface of the Kilauea rim lavas is 
the "reticulite” (Wentworth, 1938: 93) or 
"thread-lace scoria” (Dana, 1891: 163). In 
places on the northeast rim, thin patches of 
lavender clay are found on the lava under the 
reticulite, but it is not known whether this clay 
represents the remnants of an earlier explosive 
eruption deposit, or is merely surface detritus 
which was mechanically eroded from the surface 
of bare pahoehoe, concentrated into pockets, 
and mixed with accumulated humus. Oxidation 
of the glassy pahoehoe skin is found everywhere, 
though it cannot be demonstrated that this oxi¬ 
dation occurred before deposition of the reticu¬ 
lite. The surface of the clay pockets is also 
oxidized and contains humus, so it is quite 
probable that a vegetative cover had at least 
partially developed on the northeast rim prior 
to the eruption of the reticulite. This deposit 
can be found in blanket thicknesses of about 
12 inches on the north and east rims of the 
crater (Fig. 2A). Thin blanket deposits and 
pocket accumulations have been found entirely 
around the rim and as far away as the Bird 
Park. It is found under the edge of the Kea- 
moku aa flow from Mauna Loa. 
It is difficult to appraise the time interval 
between deposition of the reticulite and its 
burial by the next eruption deposit. Charcoal 
fragments are found on the surface of the 
reticulite on the northeast rim. They may be 
relics of vegetation burned by the deposition of 
the reticulite, or they may represent vegetation 
