Hawaiian Calderas — Macdonald 
323 
flowing, and continued for several kilometers 
down the mountainside. Until 1948 a crescentic 
bench (the South Lunate Platform) remained 
around the south side of the central pit, but 
it has been largely buried by the lavas and 
cones of the 1949 eruption. 
The original morphological forms of the 
calderas of the older Hawaiian volcanoes have 
been wholly destroyed by erosion, but the 
calderas are nevertheless clearly delineated by 
mapping. The lavas that filled the calderas 
are thick-bedded, generally moderately to very 
dense, and essentially horizontal, in contrast to 
the thin-bedded moderately to highly vesicular 
flows that accumulated with slopes of 2—10° 
on the flanks of the volcano outside the caldera. 
The thickness and horizontality of the caldera- 
filling flows resulted from their being confined 
within the caldera depression, and their dense- 
ness resulted from the greater proportion of 
gas that was able to bubble out of the thicker 
flows before they solidified. The contrast in 
general aspect and attitude of the two groups 
of flows is usually sufficient to indicate the 
former position of the edge of the caldera. In 
addition, banks of talus commonly formed 
against the foot of the caldera-boundary cliffs, 
as they are doing in Kilauea and Mauna Loa 
calderas today. The lavas accumulating within 
the caldera buried these taluses, and later ero- 
sion has exposed them as prisms of breccia 
between the caldera-filling and extra-caldera 
lavas. Careful mapping by H. T. Stearns has 
delineated the calderas of the Koolau and Waia- 
nae volcanoes on Oahu, and those on east Molo- 
kai, West Maui, and the exposed end of that 
of Kahoolawe. The caldera of the Koolau vol- 
cano was about 8 km long and 5 km wide, cen- 
TABLE 1 
Volumes of Caldera Collapse Compared with Volumes of Flank Lava Flows 
at Kilauea Volcano During Historical Times 
YEAR 
VOLUME OF COLLAPSE 
(m 3 ) 
VOLUME OF FLANK LAVA FLOWS (m 3 ) 
Actual 
Reduced to approximate 
volume in magma chamber 
1823 
539,500,000 
14,000,000* 
11,200,000 
1932 
580,600,000 
? 
1840 
219,500,000 
2l4,800,000 b 
171,800,000 
1868 
188,300,000 
<5,000,000 
<4,000,000 
1886 
39,600,000 
? 
1891 
34,000,000 
? 
1894 
8,500,000 
? 
1916 
8,300,000 
0 
0 
1919 
10,000,000 
73,800,000° 
59,000,000° 
1922 
21,200,000 
8,700,000 d 
7,000,000 
1924 
201,600,000 
0 
0 
1950 
0 
0 
1955 
200,000,000 
141,000,000 
113,000,000 
a Includes an estimated 2,000,000 m 3 that poured into the ocean. 
b Includes an estimated 150,000,000 m 3 that flowed into the ocean. . 
c Includes the volume of the flow in the caldera in 1919 and the flow on the southwest rift zone in 1919 and 1920. 
d Includes the volumes of flows on the caldera floor in 1921 and on the east rift zone in 1922. 
