Submarine Volcanic Eruption Research Articles

E41-09 房総沖海底地震計などで捉えられたマリアナ海底噴火に伴う T 波(第 2 報)

E41-09 房総沖海底地震計などで捉えられたマリアナ海底噴火に伴う T 波(第 2 報)

Precursory changes in fumarolic gas temperature associated with a recent submarine eruption near Izu‐Oshima Volcano, Japan

Significant temperature changes in a steamrich fumarolic gas from a deep hole in the Izu‐Oshima volcano, Japan, were observed prior to a series of earthquake swarms and submarine volcanic eruptions which occurred off the eastern coast off the Izu Peninsula, about 40 km NE of the Izu‐Oshima volcano, in July 1989. We suggest that temperature changes indicate that the Izu‐Oshima volcano and the submarine volcanic cone, the Teishi knoll, are linked and that upward movement of Teishi magma resulted in a gas pressure decrease of the Izu‐Oshima magma. This new suggestion of a link between two magma systems over such a large distance may be of great significance for understanding arc volcanism. Our observation may be of use in the future prediction of volcanic eruptions in the Izu area.

Volcanic Tremor Associated with the 1989 Submarine Eruption of Ito, Japan.

Volcanic tremor accompanied by sound was recorded on July 11 and 13, 1989, by two strong-motion accelerographs located at the east coast of Ito City in the Izu Peninsula, Japan. The tremor on July 13 was resulted from successive explosion earthquakes during a submarine volcanic eruption off Ito. Through a comparison of the tremor episodes on July 11 and 13, we found the same types of sources. Therefore, it is reasonable to postulate that volcanic explosions, small-scaled compared with those on July 13, occurred during the late evening of July 11, though no surface evidence was reported. The tremor accompanied by sound on July 11 and 13 was characterized by both high-frequency (3-30Hz) and low-frequency (0.5-1Hz) motion. The high-frequency motion corresponded to water waves and low-frequency one to both Rayleigh and Love waves. Several types of volcanic earthquakes were observed by temporary measurements during the late evening of July 11 and the early morning of July 12. These observations suggest that volcanic activity became intensified during this period and was strongly related to the creation of the Teisi Knoll.

Reflection Profiles of the Active Seismic and Volcanic Region off the East Coast of Izu Peninsula.

VIBROSEIS reflection explorations profiled the crustal structure under the east coast of Izu Peninsula where a seabed volcano erupted on July 13, 1989. Profiles along two exploration lines show a common feature that consists of three layers. The uppermost layer is floored with relatively intense reflections from shallow depths within 0.5s of two-way travel time, the next one is rather transparent layer, and the last is the basement ceiled with weaker reflections around 1.0s. The shallower reflectors are seen to be broken here and there. The depth of deeper reflector correctly coinsides with the upper limit of the earthquake swarm which is concentrated to the depth range of 2-4km. It is the most interesting that narrow spot-like high velocity bodies are found in the shallowest crust near the seismic swarm area. We suppose that those bodies may be interpreted as aged magma intrusions, and may create an asperity of the major earthquake of M5.5 prior to the submarine volcanic eruption.

Fixed-Point GPS Observation of Crustal Movement Associated with the 1989 Seismic Swarm and Submarine Volcanic Activities off Ito, Central Japan.

Continuous geodetic baseline measurements using the fixed-point GPS baseline determination network have been undertaken in the Kanto-Tokai district, central Japan. A crustal deformation which was associated with the 1989 seismic swarm and which preceded a volcanic eruption east of the Izu Peninsula was observed. We observed time variations of a 10km length baseline vector between Hatsushima (HTS) and Ito (ITO) across the swarm area, as well as those of a 40km length baseline vector between HTS and Shimoda (SMD). It was found that the position of ITO, south of the activity region, moved 8.2cm southward, 2.5cm eastward and 8.7cm upward, and the position of HTS, north of the region, moved 8.6cm eastward, 5.5cm northward and 3.3cm upward, resulting in the baseline extension of 14.5cm during the period of the active swarm prior to the submarine volcanic eruption. The detected crustal movements were found to be consistent with a proposed fault model.

Continuous Monitoring of Crustal Activity in East Izu Peninsula by Automatic Electronic Distance Measurement.

The horizontal crustal deformation accompanying the east Izu swarm earthquakes of July 1989 was observed by the automatic electronic distance measurement. The amount of elongation of the measuring line of length 9.7km attained to 22.4cm. The earthquake with a magnitude of 5.5 resulted from right-lateral faulting with a strike of N86°W. Right-lateral strike-slip of 30cm along the fault and opening of 10cm across the fault were estimated on the basis of the amount of elongation and another data observed by the Geographical Survey Institute. A submarine volcanic eruption occurred in the central part of the fault four days after the appearance of the fault. Probably the eruption resulted from the deep-seated faulting and the observed opening across the fault plane. The crustal deformation of the east Izu area is characterized by a volumetric expansion that includes horizontal dilatation and upheaval. A speculative interpretation on the geologic processes that are occurring in the crust of the region is presented in the following. The volumetric expansion was brought about by the increase of pressure of pore-filling fluid in the crust because the east Izu area is a region of high geotherm in the Fuji volcanic belt that is abnormally activated during the past ten years. The earthquake swarm occurred as shear failure due to the decrease of effective stresses in the rock. Thermal water heated by magma in the depth of the crust will move upward in the shape of convection current and exert an additional pressure on the wall rock as a result of expansion at the level where it is coverted from a critical state of water to an ordinary gas and liquid phase.

Submarine Volcanic Eruption at Teisi Knoll off Ito in the Eastern Coast of Izu Peninsula

Submarine Volcanic Eruption at Teisi Knoll off Ito in the Eastern Coast of Izu Peninsula

口絵1:伊東沖海底火山 (手石海丘) の噴火

口絵1:伊東沖海底火山 (手石海丘) の噴火

Volcanic tremors associated with the July, 1989 volcanic activity off eastern Izu peninsulla. Analysis of data by JMA network.

On June 30, 1989, an earthquake swarm started off the east coast of the Izu Peninsula in Japan. During the activity, volcanic tremors were observed from July 11 and submarine volcanic eruptions were visually observed on July 13. In this paper, some characteristics of the volcanic tremors are investigated by analyzing the data obtained by the permanent seismic network of the Japan Meteorological Agency (JMA). The volcanic tremors occurred when the earthquake swarm activity was on the decline. The spectra of these tremors are composed of low-frequency waves (about 1Hz) and high-frequency waves (more than 3Hz). The ratio of the amplitudes of the former to those of the latter increased from July 11 to July 12, and more low-frequency waves are observed in July 13. Four isolated events which were observed from 19h 03m to 19h 05m of July 13 simultaneously with a continuous low-frequency tremor (about 1Hz) show similar spectra with those of the continuous tremor during the submarine eruptions. Hence, the continuous tremor during the submarine eruptions seems to include a lot of such events. The high-frequency waves in the tremors were predominant while explosive sounds and water domes were frequently observed, and seem to be P-waves associated with explosions at the sea bottom. The low-frequency tremors are classified into continuous tremors (about 1Hz) and surface waves associated with the explosions. As the result of particle motion diagrams at the KMT station, the low-frequency tremors associated with the explosions seem to be composed of both Rayleigh waves and Love waves and the continuous tremors seem to be composed of only Love waves. After the eruptions, intermittent volcanic tremors with small amplitude were observed until July 21. Very little high-frequency waves are found in these tremors. The predominant frequency of the tremors was about 1Hz until July 16, changing to about 1.5Hz from July 17.

１９８９年７月の伊東沖群発地震と海底噴火に対する自動光波観測

The Off-East Izu Peninsula has been a realm of active swarm earthquakes since the end of 1978. Earthquake swarms with a magnitude of around 5 have occurred once or twice a year in a belt extending in a NW-SE direction. The trend of the seismic belt coincides with the regional pressure axis inferred from many active strike-slip faults. The seismic belt is situated in the Fuji Volcanic Belt that is characterized by active volcanoes and high geotherm. The purpose of this study is to detect a mode of horizontal crustal deformation that is expected to occur before and after an earthquake swarm.A new automatic electronic distance measuring device was manufactured for this investigation. The device uses an electronic distancemeter as a sensor and is controlled by a personal computer. A measuring line was laid between Ito on the east coast of the Izu Peninsula and the Hatsushima Island in Sagami Bay. The distance between the two points is about 9.7 km. Laser beam is shot from Ito and reflected from Hatsushima. Measurements are carried out every 10 minutes. The observation was started on April 14 of 1989. Although seismicity was low and no change in distance was observed toward the end of June, a new earthquake swarm commenced to occur on June 30 in the region covered by the measuring line. Day by day earthquakes increased in number and magnitude and eventually a large earthquake with a magnitude of 5.5 struck the region on July 9.The earthquake resulted from right-lateral strike-slip faulting with a trend of N 86 °W. In accordance with seismicity the distance on the measuring line gradually increased and attained to an elongation of 22.4 cm just after the occurrence of the large earthquake. Right-lateral slip of 30 cm along the fault and opening of 10 cm across the fault were estimated on the basis of the amount of elongation and another data of 16 cm elongation that was observed on the different measuring line by the Geographical Survey Institute. A submarine volcanic eruption occurred in the central part of the fault four days after the appearance of the fault. But no considerable elongation was observed on the measuring line.Aftershocks clustered in the tension region of the right-lateral strike-slip fault. This fact as well as the opening across the fault and the volcanic eruption suggests the increase of pressure of pore-filling liquid within the crust that results from a convection current of thermal water heated by magma. The author concludes that the present earthquake swarm is a phenomenon of shear failure due to decreasing effective stress in concurrence with increasing pore pressure in the rock.

10P. Infrasonic waves observed in association with the submarine volcanic eruption off Ito.(Abstracts of Papers Presented at the Fall Meeting of the Society)

10P. Infrasonic waves observed in association with the submarine volcanic eruption off Ito.(Abstracts of Papers Presented at the Fall Meeting of the Society)

1A. Electromagnetic wave radiation associated with the submarine volcanic eruption off east of the Izu peninsula, July 1989.(Abstracts of Papers Presented at the Fall Meeting of the Society)

1A. Electromagnetic wave radiation associated with the submarine volcanic eruption off east of the Izu peninsula, July 1989.(Abstracts of Papers Presented at the Fall Meeting of the Society)

27A. Thermal water anomalies to the 1989 east off Izu peninsula earthquake swarm and associated submarine volcanic eruption in the Teishi sea-mount.(Abstracts of Papers Presented at the Fall Meeting of the Society)

27A. Thermal water anomalies to the 1989 east off Izu peninsula earthquake swarm and associated submarine volcanic eruption in the Teishi sea-mount.(Abstracts of Papers Presented at the Fall Meeting of the Society)

The Volcanic Island of Surtsey, Iceland, a Quarter-century After it ‘Rose from the Sea’

An account is given of the island of Surtsey, which rose out of the sea near the Westman Islands off the south coast of Iceland as the result of a submarine volcanic eruption in November 1963. In the nearly twenty-six years since it emerged, the surface of Surtsey has undergone rapid–on the geological time-scale–transformation especially by the actions of wind and water. Indeed the changes have been far more rapid and considerable than had been expected.Despite the harsh conditions for colonization by biota, a fair amount of vascular-plant-dominated vegetation now covers an estimated 1–2% of the surface of the island, aided particularly by winds and birds bringing in disseminules. These and other features are being studied so far as possible without disturbance. Despite a general shortage of water, as rain seeps rapidly into the surface lava, sand, or tuff, a total of 25 species of vascular plants (including one fern) have been identified as having attained ecesis on the island, but not all have persisted. Five species of birds have so far colonized Surtsey, and now nest there, in addition to which there are numerous migrants coming and going, and the overall conclusion is that, despite the generally difficult environmental conditions, ‘a flourishing growth of vegetation can be expected to develop’ eventually.These studies and their implications could be useful indicators for the possibilities of rehabilitation of land areas that have been devastated by human conflict or other abuse.

Thermal condition of Surtsey

The island Surtsey was created by a submarine volcanic eruption which started on the 14th of November 1963, 21 km southwest of the Westman Islands. Volcanic activity continued in this area for nearly 4 years. During the summer of 1979 a 181 m deep continuously cored borehole was drilled on the Surtsey island. Several temperature profiles have been measured in the hole since 1979. The results of these temperature measurements are used as the basis for a discussion of the thermal condition of Surtsey. The hypothesis that intrusions rather than pillow lavas are responsible for the excess heat content of Surtsey is favored. It is found that the 13 m thick discontinuous dike complex, observed in the drill core, is sufficient to explain the excess heat content in the vicinity of the borehole and the shape of the temperature profiles recorded. It is demonstrated that the heat transfer in Surtsey has been dominated by hydrothermal convection and that the system is vapor dominated above sea level. It is estimated that the permeability of a 40 m thick section of altered tuff below sea level is 4.1 × 10 −13 m 2, while the permeability of the unaltered tuff above sea level is estimated as 1.2 × 10 −10 m 2.

The “Hodder” Phenomenon of 1902: No-active submarine volcano off St. Lucia (Lesser Antilles)

The “Hodder” phenomenon (discoloured sea-water patches) observed in 1902 off the west coast of St. Lucia (Lesser Antilles) cannot be ascribed to a submarine volcanic eruption, since recent detailed bathymetric surveys did not reveal any active submerged volcanic edifice. It is assumed that this event was due fo fault reactivation triggered by seismic shocks occurring during a major volcanic crisis affecting Martinique and St. Vincent.

Long Waves in Ocean and Coastal Waters

Long Waves in Ocean and Coastal Waters

COASTAL EROSION OF NEW VOLCANIC ISLAND NISHINOSHIMA

A new volcanic island named Nishinoshima Shinto was formed soon after the submarine volcanic eruption occurred about 800km south of Honshu in April, 1973. The Hydrographic Department of Maritime Safety Agency has continuously observed from aircraft the phenomena of the submarine volcanic eruption as well as its growth into a new volcanic island and the process of subsequent topographical changes. The result showed that large-scale coastal erosion occurred along the south coast of the island. The coastal process of the new volcanic island is very much interesting and important for geomorphological study. The Hydrographic Department carried out aerial photogrammetric surveys of the island ten times during the period from December, 1973 to January, 1978. These surveys revealed that the new volcanic island continued to grow according to active volcanic eruptions till August, 1974. The tendency thereafter was towards the reduction in size of the island due to the tranquillization of volcanic activities and the effect of active coastal erosion. Comparing the coastline of the maximum growth in August, 1974 with the latest coastline in May, 1977, it was found that the coastline retreated maximum 170 metres along the southern coast for a distance of 900 metres. To the contrary, the coastline along the northern bay formed by the old and the new islands advanced maximum 80 metres. In the process of the retreat of the coastline, there were two remarkable erosional stages with a calm stage in-between. The first erosional stage was from August to October, 1974 when the coastline retreated maximum 120 metres. The second erosional stage was from November, 1975 to August, 1976, and the coastline retreated more than 50 metres at this stage. The coastline in the calm stage was stable and the change was negligible. The process of the coastal erosion was closely related to storms attacking this locality. Namely, five typhoons passed over this area in the first erosional stage and five others in the second stage, while there were no typhoons visited there during the calm stage. In the first erosional stage, it was the main cause of the remarkable coastal erosion that Typhoon No.16 in 1974 passed northward on the west of Nishinoshima Shinto, as it caused strong southerly wind blowing to the south coast of the island. In the second erosional stage, Typhoon No. 20 caused similar coastal erosion in 1975. It was the effect of submarine topography that the eroded area was confined to the southern coast of the new island. Nishinoshima Shinto is a central cone of Nishinoshima submarine volcano. Nishinoshima old island westward and the several reefs northward, located several hundred metres apart from the new island, are parts of a somma of Nishinoshima submarine volcano. On the other hand, there is no somma to the south of the new island, where a flat sea floor deeper than 20 metres is widely extented. Accordingly, the north and west sides of the new island are protected by the comma from wave attacker, while the south side is exposed to wave erosion. The stable coastline in the calm stage was held by the resistance of lava stuffed in craters and those flown from such craters. In the erosional stages, lava stuffed in craters remained from wave erosion and stood as stacks above the sea surface. A new abrasion plafform with a width of more than 100 metres appeared along the south coast after the coastal erosion. The terminal depth of this platform was about 15 metres, which indicated the depth of the wave base of vigorous abrasion.

Undersea volcano in the Marianas located by SOFAR

Transient underwater second signals were detected at widely spaced SOFAR depth hydrophones in the Pacific during 14 December 1973. The signals, which had sound pressure levels of up to 45 dB above background in the frequency band 10–100 Hz, were spaced from 15 sec to several minutes apart, and all came from the same source area. Preliminary SOFAR fixes obtained from selected transients plot south of Myojin volcano in the Mariana Island arc near 22°N, 145°E, and are believed due to submarine volcanic eruptions. [Supported by Office of Naval Research and Naval Ship Systems Command.]

Significance of spectral banding in hydroacoustic signals from submarine volcanic eruptions: Myojin, 1970

The 1970 submarine eruptions of Myojin volcano were both visually observed and acoustically recorded by Sofar hydrophones. The acoustic record shows sustained spectral banding except at times inferred to correspond to surface-venting eruptions. The change in spectral structure occasioned by surface-venting explosions is ascribed to a change in interference patterns when the reflecting sea surface is partly removed. The longer events with sustained spectral banding are interpreted as explosive submarine avalanching.