282 
of the cliff. At B the tuff is 3 feet thick, lies 
10 feet above the present crater floor at an 
altitude of 3,560 feet, and ends abruptly to the 
northeast against the edge of a rim block which 
has slumped about 20 feet with respect to the 
rim section in which the tuff is exposed— 
enough displacement to bury the tuff layer 
beneath the crater floor if it continues into the 
slumped block. At C the tuff is exposed at the 
base of the crater wall at an altitude of 3,590 
feet, then follows an unconformity which trun¬ 
cates some lava layers in the cliff, rising steeply 
to the southwest to an altitude of about 3,690 
feet where it levels off for a short distance be¬ 
fore it disappears to the southwest behind a 
rim block which has slumped about 300 feet 
with respect to the main crater wall containing 
the tuff outcrops (Plates 2A and 3A). 
A third occurrence of tuff, interbedded in 
lavas of crater-rim age, is found at the bottom 
of the largest tree mold under the surface 
pahoehoe flow a third of a mile northwest of 
that corner*of Kilauea crater (Doerr, 1933: 
3-7). Here, a group of koa trees apparently 
grew in soil formed on a surface blanket of 
tuff. At least 20 of these trees were surrounded, 
without being toppled over, by the last lava 
flood which covered this part of the outer slope 
of Kilauea, and molds of their trunks are pre¬ 
served in the congealed lava. The largest mold, 
having a maximum diameter of 7 feet and a 
depth of about 18 feet, is so located that it acts 
as a sump to drain the surface runoff from 
several acres, and erosion by water entering the 
mold has removed the tuff layer to form a 
cavern as much as 20 feet wide and 150 feet 
long, floored by an underlying pahoehoe lava 
surface and roofed by the bottom of the upper 
lava flow. The tuff exposed along the sides of 
the cavern ranges from 0 to 36 inches in thick¬ 
ness. It mantled the irregular surface of the 
underlying pahoehoe lava, and had been greatly 
eroded before burial by the surface flow. The 
tuff lies at an altitude of slightly over 4,000 feet. 
For reasons stated in the following paragraphs, 
PACIFIC SCIENCE, Vol. II, October, 1948 
this tuff is correlated with the Uwekahuna for¬ 
mation of the type locality. 
The type deposit of the Uwekahuna tuff (in 
the base of the northwest crater wall) ranges in 
thickness from a few inches to over 7 feet. It 
consists of several beds of fine to coarse vitric 
pumice, intercalated with variable thicknesses 
of lithic debris mantling an unmodified surface 
of pahoehoe lava. A typical section (locality S 
on Plates 2A and 2C) is: 
Inches 
Bottom of overlying lava 
Coarse vitric pumice... 3 
Oxidized desert surface 
Coarse pumice with a few lithic fragments. 6 
Oxidized desert surface 
Agglomerate of lithic dust and fragments.15 
Oxidized desert surface 
Coarse pumice with a few lithic fragments. 4 
Oxidized desert surface 
Coarse vitric pumice...... 8 
Oxidized desert surface 
Fine vitric shards grading down to coarser.12 
Surface of underlying lava flow 
Most outcrops show the five layers of vitric ma¬ 
terial separated by oxidized desert surfaces; the 
amount, coarseness, and texture of the inter¬ 
calated lithic debris vary greatly from outcrop 
to outcrop. The section on the outer slope of 
the Kilauea dome at the bottom of the tree 
mold consists of: 
Inches 
Bottom of overlying lava flow 
Vitric pumice ....... 2 
Oxidized surface 
Medium vitric pumice... 5 
Oxidized surface 
Fine to medium, bedded vitric pumice. 6 
Oxidized surface 
Fine, bedded vitric pumice. 9 
Oxidized surface 
Very fine vitric ash and pumice. 3 
Surface of underlying lava flow 
Thus, five epochs of magmatic fountaining, 
separated by times of quiet but with no inter¬ 
vening deposition of lithic debris, are repre¬ 
sented at the tree mold locality. If the variable 
lenses of intercalated lithic debris are ignored 
in the type section, the five vitric layers in the 
