Eruptions of Kilauea—POWERS 
283 
type sections of the Uwekahuna tuff may be 
correlated satisfactorily with the five vitric layers 
found at the tree mold locality. Future study 
may indicate that the lithic debris represents 
deposits from phreatic eruptions; the present 
evidence suggests that the composition and dis¬ 
tribution of the lithic lenses are too erratic even 
to represent phreatic eruption deposits. At 
present it is thought that they are talus debris 
and outwash material interbedded with the 
mantle deposits of pumice on the floor of an 
old crater near the base of an old crater wall. 
Of the tuff pictured in Plate 2B, Sidney 
Powers (1916: 230) gives the following de¬ 
scription: "The beds are composed principally 
of yellow ash with some rock-fragments 1-2 
inches in diameter, lava droplets, thread-lace 
scoria, and a few bombs 6 inches in length.” 
Wentworth (1938: 88) discounts the possible 
correlation of this tuff with the Pahala tuff. 
Macdonald thinks it may be a continuation of 
the tuff still exposed northeast of Uwekahuna 
and it is so considered by the writer. 
To the northwest and the northeast, beyond 
the edge of Kilauea surface flows, a deposit of 
partly consolidated crystal-vitric tuff is found 
which possibly correlates in age with one of 
these Uwekahuna magmatic eruptions. In the 
Bird Park area (Fig. 1), this bed lies on pala- 
gonitized Pahala tuff under the edge of an aa 
flow from Mauna Loa, which in turn is older 
than the lowest member of the Kilauea surface- 
ash deposits. About two miles northeast of 
Kilauea, at about 3,800 feet (locality D, Fig. 1), 
a bed of coarse, slightly palagonitized vitric 
shards lies on top of the completely palagoni¬ 
tized Glenwood tuff under a layer of unaltered 
surface ash from Kilauea. 
All of these tuff deposits are considered parts 
of the same formation—the Uwekahuna tuff— 
deposited on different parts of an older Kilauean 
dome with a collapse caldera in the summit. 
The tuff is considered to be the remnant de¬ 
posits of five epochs of intense lava fountaining 
or magmatic explosion separated by intervals 
of relative quiet measured in at least tens of 
years. 
Studies now in progress on the rate of refor¬ 
estation in given climatic zones may eventually 
yield data making useful the state of reforesta¬ 
tion as a quantitative indicator of elapsed time 
since a given area was a new volcanic surface. 
At present, the use of forest growth as an 
indicator of the age of a surface is not much 
better than intelligent guessing, but one is 
tempted to use it in evaluating the lapse of time 
between the eruption of the pre-Uwekahuna- 
tuff pahoehoe flow and the destruction of the 
koa grove by the post-tuff flow at the tree mold 
locality. Present climatic conditions between 
the tree mold locality and an area just north¬ 
east of Keanakakoi are not widely different; 
the average annual rainfall is approximately 60 
to 70 inches at both places, with slightly more 
fog at the tree mold area. Deposits from the 
1790 eruption average over a foot thick on 
the Kilauea rim just north of Keanakakoi, but 
thin to 3 inches in less than a quarter of a 
mile to the northeast. The present surface is 
practically barren of tree growth north of Kea¬ 
nakakoi, but supports a dense forest of ohia and 
amaumau fern a quarter of a mile to the north¬ 
east. In fact, the transition from dense growth 
to barren surface occurs in a zone about 300 
yards wide in which scattered trees and ferns 
have obtained a foothold (Plate 1A). The 
conclusion seems justified that the 1790 deposit 
killed the surface vegetation up to a fairly 
sharp line and that the advance of reforestation 
over the new surface has progressed about 300 
yards in 150 years. Judging from the present 
relationship of the slopes of Kilauea to the 
forested slopes of Mauna Loa, the tree mold 
area could not have been closer than half a 
mile (probably a mile) to living koa forest 
after the eruption of the pre-Uwekahuna sur¬ 
face lava flow. The trees which formed the 
molds hardly could have obtained foothold until 
the end of the second Uwekahuna magmatic 
explosion since its eruption of 9 inches of 
pumice at this spot probably would have killed 
