Impact Scars at Kilauea 1 
Chester K. Wentworth 2 
Kilauea caldera is an ellipsoidal area about 
two by three miles in extent, whose floor 
around its eastern, northern, and northwestern 
margins stands 200 to 500 feet below the 
surrounding surface of Kilauea volcano. At 
the southwest the caldera is open at grade and 
any copious lava flow would pass out and 
down the south slope of the volcano. The 
floor of the caldera is a low basaltic shield 
which at its apex, around Halemaumau, 
stands more than 200 feet above the lower 
parts of the northeast margin. 
Halemaumau, the so-called firepit, is at 
present somewhat more than 3,000 feet in 
diameter, and its floor, at about 450 feet below 
the rim, consists of the surface of the 1954 
lava flow, with a few protruding cone rem- 
nants from the more bulky 1952 flow. The 
floor of the caldera to the north, east, and 
northeast of Halemaumau consists of pahoe- 
hoe lava flows marked by tumuli and other 
characteristic features. Parts of the area to the 
west and south show the fresh surface of the 
1921 lava flow, but more of the area to the 
south and west is mantled by ash beds and 
by thin layers and surface windrows of pu- 
mice. Surrounding Halemaumau, which was 
enlarged greatly by phreatic explosions in 
1924, the surface of the caldera floor is strewn 
with blocks thrown out at that time and 
1 Publication authorized by U. S. Geological Survey. 
Manuscript received July 2, 1956. 
2 Hawaii National Park, Hawaii. 
ranging up to several feet in diameter. On 
the eastern side, where the blocks landed on 
bare lava flows, in many instances the blocks 
broke through the surface lava layers into 
blister or other cavities beneath. Some re- 
mained in the holes and others ricocheted 
beyond, commonly showing their origin from 
the direction of the firepit. On the western 
side, the ash layers were thicker and offered 
more cushioning; here there are a few impact 
craters where blocks fell, but these are not 
as conspicuous as those of another older 
series which are to be described in this paper. 
The limits to which blocks of the 1924 ex- 
plosive eruption were thrown are easily seen 
in the field. The holes in the lava are shown 
in Figure 1. 
The caldera margin, from the east side 
around to the north and west and to the 
southwest of Halemaumau, is a rock cliff in 
which the lava flow section is clearly exposed. 
The southeast and south margin falls in an 
area where ash layers from successive erup- 
tions amount to 30 or more feet in thickness. 
Along this line the surface faulting is com- 
pound and the ash section shows several 
parallel cracks with displacement along some. 
The hard rock margin is exposed in only a 
few places. To the south and southwest, the 
margin of the caldera is outlined by a rolling, 
sand-covered surface, with lava rock a few 
feet down, but exposed only in gullies that 
notch the margin. 
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