Hachijo Island Research Articles

TRANSPACIFIC DETECTION OF MYOJIN VOLCANIC EXPLOSIONS BY UNDERWATER SOUND

On 17 September 1952 a fishing boat, the MYOJIN MARU, discovered a submarine volcanic eruption 200 nautical miles south of Tokyo. The volcano appears to be the central cone of a caldera lying along the Fuji volcanic zone. The near-by Bayonnaise Rocks mark the highest, and the only subaerially exposed, portion of the caldera rim. A series of great explosions accompanied the extrusion of augite-hypersthene dacite. Since 26 September, when the main series of explosions ended, there has been only sporadic activity. Because of its remoteness, only a few visual observations of Myojin were made. Additional data were obtained from a tsunami recorder on Hachijo Island, 130 kilometers north of Myojin, which detected several tsunamis initiated by the volcanic eruptions, and by an atmospheric electricity recorder at Tokyo which detected atmospherics associated with the eruption. In contrast, a rather complete record of the Myojin activity was recorded by the U. S. Navy Sofar stations at Point Sur and Point Arena, California, about 8600 kilometers from the scene. More than 100 explosions were detected, one of which lasted for more than an hour. Explosions recorded on Sofar equipment agree in time with those observed visually or inferred from tsunami and atmospherics data. From the tsunami data and the Sofar records, it was independently concluded that the explosion which destroyed the Japanese Hydrographic vessel, No. 5 KAIYO MARU, occurred at about 1220 JST on September 24. All 31 people aboard the vessel were lost. This is believed to be the first time any signals on Sofar records have definitely been identified as of volcanic origin, and, since some of the signals were distinctive, installations similar to those of Sofar stations may prove of value for monitoring oceanic volcanic activity.

Preliminary Report on the Marine Diatoms from Hachijô Island, Japan

Hachijo Island, one of the Zunan Group (or Izu Islands), is located at lat. 33° 02'-09' N and long. 139°43'-52' E, 157 miles south of Tokyo, just exposed to the great warm current, “Kuroshiwo.” The plankton materials dealt with here are those collected five times in the coastal waters beyond the breakwater, nine times at the beach, and twice in the tide pools of the island, covering the years 1950, 1951, and 1952. All were collected by means of plankton net of ordinary type, made of bolting cloth of 128 meshes a linear inch.

恙虫の生態に関する研究 (II) : Trombicula scutellaris Nagayo et al. 1921 の地表分布について

In the previous paper of this series on the ecology of trombiculid mites, some accounts of the collecting method using bakelite plates were reported. The technique made it possible to survey the unengorged stage of the larvae of chigger in natural conditions on the fields. The unengorged larvae are the very stage which attack human or other hosts and are of epidemiological importance. The present study was designed to obtain the informations about the surface distribution of Trombicula scutellaris Nagayo et al, 1921, which is suspected to be the vector of Shichito Fever, the scrub typhus in Izu Seven Islands of Tokyo. The experiments were conducted at the Hachijo Island, the most southern one in the Archipelago, in December 1953, during the season of the endemic. Small bakelite plates (5×5cm^2) were placed upon the surface of the ground and the number of chigger mites that crawled up to the plate after 5 minuites was observed. To survey all over the surface of 1 square meter ground, two hundred and twenty two sheets of small plate were used. They were sufficient to cover nearly all of the surface of 1m^2 area. The temperature and relative humidity (2 cm height over the surface), the illuminating intensity, pH of soil at the surface and the soil temperature (10cm beneath the surface) were also observed at 25 points in the area. The results of the experiments indicate that the unengorged larvae of Tr. scutellaris are not scattered at random on the ground surface, but they form a certain type of congregation or patch. The findings that support this view are as follows : 1. The frequency distribution of the observed number of mites per plate did not fit to that of Poisson's distribution. 2. The divergence coefficient (F_0=V/X^^-) was obviously larger than 1. 3. The gamma type compound of Poisson distribution fitted to our case. 4. Un-uniformity of numbers of scattered mites was also shown by the analysis of variance. 5. The spacial correlation was examined according to the method introduced by Student (1907). 6. It was pointed out that both the structural correlation coefficient (r) and ratio (η) were not zero, and r>0, η>0 were confirmed. Thus the surface distribution of this chigger mite was shown not to be that of "by chance, " and the structure of spacial distribution apparently consisted of patches. The correlations between the observed number of chiggers and the micro-meteorological observations were also examined. The results showed that the temperature had positive correlation with the number of chiggers and the humidity negative one. The soil temperature, illuminating intensity and soil pH were found not to have any correlation.

On the Diplopods collected in the Seven Islands of Izu, Japan

One of the authors previously investigated on a few diplopods collected on Hachijo Island, the Seven Islands of Izu. Recently we were fortunate enough to study 25 specimens brought back from these islands by Mr. T. Aoki in 1949, 1951 and 1952. Besides these seven more specimens have been presented to us by Mr. K. Shinohara. Thus we have at our disposal nine species of millipedes, five of which are considered to he new to the fauna of the Seven Islands of Idz. The diplopod fauna hitherto known from these islands are as follows: -Polyxenidae 1 Monographis takakuwai nigricans Miyosi Hachijo 1. Strongylosomatidae 2* Haplogonosocna silvestre dichotomum Takakmva Oshima 1. 3 Orthomorpha gracilis (C. L. Koch) Hachijo I., Niijima 1. 4* Nedyopus cingulatus (Attems) Hachijo 1. Polydesmidae 5 Epanerchodus jägerskiöldi insularum Verhoeff Oshima 1. Cryptodesmidae 6 Niponia nodulosa Verhoeff Hachijo 1. Oniscodesmidae 7* Kiylindogaster sp. ? Hachijo 1. 1)iplomaragnidae 8* Syntelopodemna sp. Oshima 1. Blaniulidae 9 Skleroprotopus insularum Verhoeff Oshima 1. Julidae 10 Fusiulus quadrates Takakuwa Oshin a I., Niijima 1. 11* Amblyiulus sp. ? Niijima I. Among the above no. 5 and no. 9 have been recorded by the late Dr. K. W. Verhoeff while no. 8 was identified basing on two males brought back from Oshima Island by Mr. Shinohara. Asterisks are given to species new to the fauna of this area.

Cygnus olor (Gmelin) obtained in Hachijo I., the Seven Islands of Izu

Mr. G. Okuyama in November, 1933 procured a swan on Hachijo Island, one of the Seven Islands of Izu and, it was identified by Mr. Tokutaro Momiyama (1939) as Cygnus cygnus (specimen no. 340033).I have recently exmined this specimen and found out that it is Cygnus olor, not C. cygnus as formerly considered it to be. This fact constitutes the first record of the Mute Swan found in the Japanese Islands.

On spiders collected on Hachijo Island and Aogashima Island, Seven Islands of Izu

On spiders collected on Hachijo Island and Aogashima Island, Seven Islands of Izu

The industry of Hachijo island (Local forestry)

The industry of Hachijo island (Local forestry)

三宅島, 八丈島住民の體質人類學的研究

三宅島, 八丈島住民の體質人類學的研究

Notes on Centipedes collected by Mr. Fajiyama in Hachijo Island

Notes on Centipedes collected by Mr. Fajiyama in Hachijo Island

八丈島に於ける大雨の強度に就て

八丈島に於ける大雨の強度に就て