マラッカ海峡の Sand Wave

抄録

The existence of sand waves in the region as shown in Fig. 2 was confirmed by the Joint Survey Team from Indonesia, Japan, Malaysia and Singapore during the preliminary hydrographic survey in the Malacca and Singapore Straits conducted from January to March 1969.
The sand waves as appeared on echograms can be classified into the following categories :
A. Round top type group I : a. Round top type (Fig. 3)
b. Conical type (Fig. 4)
C. Compound round top type (Fig. 5)
B. Round top type group II : a. Asymmetric round top type (Fig. 6)
b. Asymmetric compound round top type (Fig. 7)
C. Pinnacle type group : a. Pinnacle type (Fig. 8)
b. Asymmetric pinnacle type (Fig. 9)
c. Asymmetric compound pinnacle type (Fig. 10)
The distribution of sand waves according to their types is as follows :
(a) Pinnacle types sand waves are developed in the area extending from the SE extremity of Malay Peninsula to Singapore offing, and their wave-heights are 8 to 15 metres.
(b) In the area between SW tip of Singapore island and Benut offing, mixed existence of round top type group I and pinnacle type group is found.
(c) Various types are found between Tg. Tohor and One Fathom Bank, but pinnacle type waves are prevailing in the offing between Tg. Tohor and Muar, where the largest sand wave (of a pinnacle type with a height of 20.6 metres and a length of 267 metres) was found. Sand waves of pinnacle type and round top type group II were seen off the coast from Muar to Cape Rachado, and their heights were 5 to 10 metres.
(d) Between Cape Rachado and One Fathom Bank, those of pinnacle type and round top type group II with heights of more than 10 metres were found, among which where included those with heights reaching 15 to 18 metres.
Of sand waves surveyed in the detailed survey area off Cape Rachado, 1, 144 waves were calculated as to their various factors for classification, and the following data were obtained :
(1) Average wave-height and average wave-length.
(2) Correlation between the height and length of waves (Fig. 14 and 15).
(3) Relation between the water depth and existence ratio of each type of wave (Fig. 16).
(4) Relation between the wave height and the existence ratio of each type of wave (Fig. 17).
Causes for creation of sand waves and their movements were not studied in this paper, since this was the first time of study and, besides, detailed observations were not conducted for currents and tidal currents in the area in question.