Geomorphic Contrasts in Koolaus — Palmer 
Fig. 18. Possible unconformity 0.7 miles west of 
Pearl City Junction. See Figure 12 for the location. 
ted, except to note that the Waianae Lava 
Shield had been built and considerably eroded 
before the Koolau vents discharged any of 
the flows that overlap the east side of the 
Waianae Range.) 
According to the new interpretation, the 
first Koolau episode was the building of the 
southeastern end of the present Koolau 
Range, making a somewhat elliptical dome 
or shield with a base of the order of 15 by 
20 miles. The lavas of this episode are named 
"K-l" on the tentative map (Fig. 19). Flows 
on the leeward side dip 6° to 9° (Stearns, 1939, 
pi. 2). Those on the windward side presum- 
ably had similar dips, but this cannot be 
observed because so much of the original 
shield has been removed. When this eruptive 
activity died out, stream erosion became dom- 
inant and deep valleys were cut in the dome. 
It is my opinion that a considerable part of 
the windward side of this shield was dropped 
down along a fault or fault zone, and that the 
fault scarp has receded some miles as a result 
of various erosional processes. 
Subsidence of part of the shield lowered the 
Honolulu area 800 or 1,000 feet. Data are not 
available for estimating the lowering in the 
Waimanalo and Kailua part of the windward 
side, but the fairly wide and level floors of 
Punaluu and Kahana valleys suggest sub- 
sidence of a few hundred feet, followed by 
sedimentation in the bays made by drowning 
the valley mouths. Northwest of Punaluu 
there is little or no evidence of significant 
subsidence of the windward side. 
315 
It is now suggested that a second episode 
of volcanic activity built a somewhat elong- 
ated ridge northwestward for 20 or more miles 
from the northwest end of the first oval shield. 
This ridge was about ten miles wide, and was 
built of the lavas that came up along nu- 
merous sub-parallel dikes of the "dike com- 
plex." It is indicated as "K-2" on the tenta- 
tive map (Fig. 19). Though on a much smaller 
scale it is somewhat analogous to the ridge 
that has been built up by lavas from the 
southwest rift of Mauna Loa. Stearns (1939, 
pi. 2) reports dips of 7° to 10° on the wind- 
ward side of this part of the Koolau Range. 
Data on dips are probably not obtainable on 
the leeward side, but are presumably similar. 
Dividing the constructional history of the 
higher parts of the Koolau Range into two 
Fig. 19- Tentative map of areas built during the 
suggested eruptive episodes in the construction of the 
Koolau Range. The Honolulu Volcanic Series, solid 
black, is from Wentworth and Winchell (1947). 
episodes, K-l and K-2, will explain the con- 
trasts between the southeastern and north- 
western ends as regards (1) the windward 
aspect, i.e., alcoves vs. valleys, (2) the degree 
of indentation of the main Crestline, (3) the 
relative amounts of area above the 2,000-foot 
level, (4) the shapes of the leeward valleys, 
and (5) the inland pair of cross profiles (Fig. 
10 b). The isohyetal map (Fig. 7) shows abun- 
dant, and about equally abundant, rainfall 
along the upper parts of the whole range, so 
that differences in rainfall cannot account for 
