Myojin-sho
Encyclopedia
is a submarine volcano
located about 450 kilometers south of Tokyo
on the Izu-Ogasawara Ridge in the Izu Islands
. Volcanic activity has been detected there since 1869. Since then it has undergone more eruptions, the most powerful of which resulted in the appearance and disappearance of a small island
.
The name Myōjin-Shō derives from a fishing boat, No.11 Myōjin-Maru of Yaizu City, Shizuoka Prefecture
, the crew of which first witnessed the major volcanic eruption of 1952.
Department of the Maritime Safety Agency, was destroyed by the volcano, with the loss of its crew of 31 (including the nine scientists studying the eruption). Consequently the Department developed Manbou (Sunfish), an unmanned radio operating survey boat, and has used it for the research of dangerous sea areas such as submarine volcanoes.
This was the first time that volcanic activity had been detected using the SOFAR channel
.
around Myōjin-Shō was made for the first time.
Manbou II conducted the survey of the sea area within a radius of 3 nautical mile
s (about 5.4 kilometers) of Myōjin-Shō. Shoyo conducted the survey of the sea area within a radius of about 10 nautical miles (about 18.5 kilometers) but farther than the area of the radius of 3 nautical miles (5.6 km). Manbou II works by the order of preprogrammed instructions and measures depth and water temperature. Bathymetric survey of Manbou II was carried out by using the "PRD-601" echo sounder at intervals of 0.2 nautical miles (about 370 meters). Shoyo conducted a comprehensive survey including the geological and geophysical surveys of sea bottom.
Bathymetric survey of Shoyo was carried out by using a "Seabeam 2112" echo sounder at intervals of 0.5 nautical miles (about 930 meters).
(rocks of 9.9 meters in height above the sea level) as a portion of the somma
(Mita, 1949). As a result of the survey, however, the authors found that both Myōjin-Shō and the Bayonnaise Rocks are cones on the somma of a double volcano. The foot of this double volcano lies 1,400 to 1,500 meters in depth and the size is about 30 by 25 kilometers east-west, north-south. The somma is almost a circle in the diameter of 7 by 9 kilometers and the height is 1,000 – 1,400meters.
The diameter of the caldera floor is 5.6 kilometers and about 1,100 meters in depth. The central cone is a high formerly known as Takane-Sho, 328 metres below sea level.
Myōjin-Shō is a post caldera cone formed in the northeastern part of the somma of the double volcano. It is the single conical cone and the height is 550 meters with the shallowest depth 50 meters. A record that suggests a gushing of bubbles near the summit was obtained and the micro earthquake were observed near the Myōjin-Shō, showing that the volcano is still active, although at a low level.
Submarine volcano
Submarine volcanoes are underwater fissures in the Earth's surface from which magma can erupt. They are estimated to account for 75% of annual magma output. The vast majority are located near areas of tectonic plate movement, known as ocean ridges...
located about 450 kilometers south of Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
on the Izu-Ogasawara Ridge in the Izu Islands
Izu Islands
The are a group of volcanic islands stretching south and east from the Izu Peninsula of Honshū, Japan. Administratively, they form two towns and six villages; all part of Tokyo. The largest is Izu Ōshima, usually called simply Ōshima....
. Volcanic activity has been detected there since 1869. Since then it has undergone more eruptions, the most powerful of which resulted in the appearance and disappearance of a small island
Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...
.
The name Myōjin-Shō derives from a fishing boat, No.11 Myōjin-Maru of Yaizu City, Shizuoka Prefecture
Shizuoka Prefecture
is a prefecture of Japan located in the Chūbu region on Honshu island. The capital is the city of Shizuoka.- History :Shizuoka prefecture was formed from the former Tōtōmi, Suruga and Izu provinces.The area was the home of the first Tokugawa Shogun...
, the crew of which first witnessed the major volcanic eruption of 1952.
Eruption of 1952-3
The volcanic eruption from 1952 to 1953 was one of its biggest activities on record, with the repetitious appearance and disappearance of an island, which at one point reached over ten metres above sea level, before sinking after a severe volcanic explosion in September 1953. On September 24, 1953, a survey vessel, No. 5 Kaiyo-Maru of the HydrographicHydrography
Hydrography is the measurement of the depths, the tides and currents of a body of water and establishment of the sea, river or lake bed topography and morphology. Normally and historically for the purpose of charting a body of water for the safe navigation of shipping...
Department of the Maritime Safety Agency, was destroyed by the volcano, with the loss of its crew of 31 (including the nine scientists studying the eruption). Consequently the Department developed Manbou (Sunfish), an unmanned radio operating survey boat, and has used it for the research of dangerous sea areas such as submarine volcanoes.
This was the first time that volcanic activity had been detected using the SOFAR channel
Sofar channel
The SOFAR channel , or deep sound channel , is a horizontal layer of water in the ocean at which depth the speed of sound is minimal. The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating...
.
Survey of 1998-9
In 1998 and 1999, the Hydrography Department conducted comprehensive sea bottom surveys around Myōjin-Shō, using the state-of-the-art survey vessel Shoyo and Manbou II, the second generation Manbou. As a result of these surveys, a detailed picture of the sea bottom topographyTopography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
around Myōjin-Shō was made for the first time.
Manbou II conducted the survey of the sea area within a radius of 3 nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
s (about 5.4 kilometers) of Myōjin-Shō. Shoyo conducted the survey of the sea area within a radius of about 10 nautical miles (about 18.5 kilometers) but farther than the area of the radius of 3 nautical miles (5.6 km). Manbou II works by the order of preprogrammed instructions and measures depth and water temperature. Bathymetric survey of Manbou II was carried out by using the "PRD-601" echo sounder at intervals of 0.2 nautical miles (about 370 meters). Shoyo conducted a comprehensive survey including the geological and geophysical surveys of sea bottom.
Bathymetric survey of Shoyo was carried out by using a "Seabeam 2112" echo sounder at intervals of 0.5 nautical miles (about 930 meters).
Structure
Previously, Myōjin-Shō was considered to be the central cone of a double volcano with the Bayonnaise RocksBayonnaise Rocks
is a group of volcanic rocks located in the Philippine Sea approximately south of Tokyo and south-southeast of Aogashima, in the southern portion of the Izu archipelago, Japan...
(rocks of 9.9 meters in height above the sea level) as a portion of the somma
Somma volcano
A somma volcano is a volcanic caldera that has been partially filled by a new central cone. The name comes from Mount Somma , a stratovolcano in southern Italy with a summit caldera in which the cone of Mount Vesuvius has grown.A number of the world's best examples of somma volcanoes are found on...
(Mita, 1949). As a result of the survey, however, the authors found that both Myōjin-Shō and the Bayonnaise Rocks are cones on the somma of a double volcano. The foot of this double volcano lies 1,400 to 1,500 meters in depth and the size is about 30 by 25 kilometers east-west, north-south. The somma is almost a circle in the diameter of 7 by 9 kilometers and the height is 1,000 – 1,400meters.
The diameter of the caldera floor is 5.6 kilometers and about 1,100 meters in depth. The central cone is a high formerly known as Takane-Sho, 328 metres below sea level.
Myōjin-Shō is a post caldera cone formed in the northeastern part of the somma of the double volcano. It is the single conical cone and the height is 550 meters with the shallowest depth 50 meters. A record that suggests a gushing of bubbles near the summit was obtained and the micro earthquake were observed near the Myōjin-Shō, showing that the volcano is still active, although at a low level.