Geomorphic Contrasts in Koolaus — Palmer 
313 
the vents that yielded the lavas that built the 
Wahiawa Plateau and related, rather smooth 
surfaces. 
ENVELOPES OF CONTOUR LINES 
The levelness of the Wahiawa Plateau, or 
the gentleness of its slopes, is brought out 
by a study of the "envelopes” of the 500-, 
Fig. 14. Map of lateral lava shields northwest of 
Wahiawa. Contour intervals of 10 and 50 feet. 
1,000-, 1,500-, 2,000- and 2,500-foot contour 
lines on the lee side of the Koolau Range 
(Fig. 12). The envelopes were constructed by 
marking the down-slope salients of the re- 
spective contour lines on the 1938 U. S. 
Geological Survey topographic map of Oahu, 
on the 1:62,500 scale. Then the salients were 
joined freehand by a smooth line, thus out- 
lining the original form of the volcanic pile. 
It will be noted that in the southeastern 
area the selected envelopes are only a mile or 
so apart, in general, indicating fairly steep 
slopes. In the northwestern part, however, 
they are in general twice as far apart indicating 
the gentler slopes of the suggested, additional 
volcanic episode. 
LATERAL LAVA SHIELDS 
There is no definite evidence as to the lo- 
cation of the eruptive vents that supplied 
most of the lavas that built the Wahiawa 
Plateau and its related surfaces. The suggested 
prolongation of the Waimea Fault as the locus 
of vents is only an hypothesis. 
There are, however, certain minor, lateral 
vents indicated by half a dozen low but broad 
hills between Kipapa Gulch and Poamoho 
Gulch (Fig. 13). These small hills slope gently 
outward in all directions from their low sum- 
mits, so that their slopes are in part in the 
reverse direction to the usual, roughly west- 
ward slope of the "plateau.” Although they 
are much smaller they resemble to some 
degree the lateral lava shield named Mau- 
naiki, which was built by a flank eruption 
from the southwest rift of Kilauea in the 
winter of 1919-1920. Lava that had drained 
from Halemaumau is thought to have moved 
underground along the rift for a way, and 
then to have come to the surface to build 
Maunaiki. Such structures are called lateral 
lava shields. 
Three of the lateral lava shields, northwest 
of Wahiawa, are aligned as if their lavas had 
come from points along a rift or fissure bear- 
ing about N. 70° W. (Figs. 14 and 15). Two 
lateral lava shields, a little south of the Wai- 
ahole Aqueduct, one on either side of Kame- 
Fig. 15. The lateral lava shield in the northwest 
comer of the big triangle of roads in Figure 14. 
hameha Highway, suggest a fissure bearing 
about S. 80° W. (Figs. 16 and 17). 
Stearns (1940: 5 and pi. 1) suggested that 
the unexpectedly high ground water body, 
in the central part of the Wahiawa Plateau, 
was held up between dikes, and gave a map 
showing by two boundary lines the presumed 
extent of the high-level ground-water body. 
