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Jim KAUAHIKAUA,**.  -  ,-  ,**/  -  ,- Morphometric Study of the Lava Entering the Sea : the +33* Kaimu Bay Flowfrom Pu’u ‘O’o-Kupaianaha Vent, Kilauea Volcano, Hawaii
Miyuki NONAKAῌ, Susumu UMINOῌῌ and Jim KAUAHIKAUAῌῌῌ
The Pu’u ‘O’o-Kupaianaha eruption of Kilauea Volcano has been active since +32- and e#used ,.- km- oflavas by September ,**,. In +33*, lava ﬂows fed by tubes from Kuapainaha vent covered Kalapana Village andentered Kaimu Bay. Kaimu Bay was covered with “main lobes” emplaced parallel to shoreline and “outﬂows”
emplaced between the main lobes. The edges and surfaces of main lobes are often covered with thin pahoehoe
lobes, and have clefts and pits on the surface formed by inﬂation of the lobes. Flow directions of main lobes
indicated from buckled ropy wrinkles were parallel to shoreline, and new lobe branched from edge of older lobe
also ﬂowed along the older lobe. The lava lobes are holohyaline at their surface with sporadic varioles ofclinopyroxene, and become intersertal at the interiors with increasing microcrystals of plagioclase andclinopyroxene. The solidiﬁcation temperature of lava estimated from MgO content in the glass of the lobe surface
is ++.* (-) . On the other hand, the temperature of lava on Kupaianaha and Pu’u-O’o lava lake is ++/. (-) , the di#erence is only +. when lava carried to Kaimu Bay over ,* km away from vent, hence tube system
keep high adiabatic e#ect. At the last period of Kaimu bay ﬂow, the temperature of lava is ,*ῌ,. lower than
the former period. This suggests that whole tube systems in Kaimu bay cooled by air, and molten lava stagnatedin lava lobes at the last period. As examined daily outline of expanding ﬂow lobes from observation data of lava
ﬂows from land and air by Hawaiian Volcano Observatory and morphometric survey of present lava lobe on
Kaimu bay, a mean supply rate of lava ﬂux to Kaimu Bay was 22,*** m-/day during 21 days from 0 August to ,0October. It is consistent with other data of Pu’u ‘O’o-Kupaianaha eruption.
The emplacement and development process of lava lobes on Kaimu bay is inferred as following : When lava
entered the sea, front part of lava was solidﬁedy by rapid cooling of water. Although following molten part
avoided solidiﬁed front part, it also entered the sea and was solidiﬁed by rapid cooling of water. Lava lobe makes
barrier to the sea and ﬂow along shoreline. Soon, lava lobes stopped from gentle cooling by air and beganinﬂation due to injection of molten lava. Clefts on “main lobes” resulted from inﬂation of lava and “outﬂows”
from leakage of molten lava from clefts. When internal pressure rise due to injection of molten lava got over thetensile strength of crust, cracking and large drainage of molten lava occurred, new lobe formed and ﬂew alongolder lobe. Finally, shallow zone of Kaimu bay was buried by many lava lobes parallel to shoreline.
Key words : Kilauea Volcano, Kaimu Bay, lava lobes, entering the sea, morphometry
.,,ῌ2,/3  2-0 !"#$%&&Department of Biology and Geosciences, Faculty ofScience, Shizuoka University, 2-0 Oya, Shizuoka .,,ῌ2,/3, Japan.
'() : ++-ῌ**-, *+,-+./ +ῌ+ῌ+*+"012(Present address : Earthquake Research Institute, theUniversity of Tokyo, +ῌ+ῌ+, Yayoi, Bunkyo-ku, Tokyo++-ῌ**-,, Japan.
.,,ῌ2/,3  2-0Faculity of Science, Shizuoka University, 2-0 Oya,Shizuoka .,,ῌ2/,3, Japan.
U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 3202-, U.S.A.
Corresponding author : Miyuki Nonaka
e-mail : nonaka-m@eri.u-tokyo.ac.jp