11:00 AM - 1:00 PM
[MIS16-P05] Development of Ocean Bottom Mounted Turbidity Current Detector (TCD)
Keywords:Turbidity Current, Suruga bay, Instrument Development
In August 2018, sub-surface Structure Exploration based on the research title "The integrated research project for the Fujikawa fault zone" (Research Delegate Prof. Hiroshi Sato) was began in the northern Suruga Bay. We have mounted eighteen (18) pop-up type Ocean Bottom Seismographs (OBS) along planned survey line (from Shimizu to Heda). Typhoon No. 24 had been passing around the vicinity of Suruga Bay in the period from September 30 to October 1 2018. After the typhoon passed, it was revealed that three (3) OBS were drifted from extension of the mouth of Fujikawa estuary area supposed to be affected by Turbidity Current, and spread into central Suruga Bay (Baba et al., 2021).
We also conducted a trace survey of this turbidity current using the R/V Shinsei Maru (KS-21-1 Cruise). The results of this KS-21-1 Cruise will be presented separately in this meeting.
In the cases of submarine landslides such as influenced to Sulawesi Is. (Indonesia), September 2018, or turbidity currents as earthquake off Pacific coast of Tōhoku (Japan), March 2011, both cases associated with large earthquakes, there have been cases where became the source of Tsunami and cause of damages.
In addition, when large typhoons hitting coastal land areas and short torrential rain also become some major cause of turbidity currents, as they supply large amounts of sediment from rivers into the coastal waters in a short period. According to the recent global trend, human casualties are increasing caused by the number of large or super typhoons. First-class Rivers (Fujikawa, Oigawa, Abekawa, Kanogawa) flowing into the Suruga Bay, and the seafloor topography of Suruga bay is quite complicated. Therefore, there is possibility of occurrence of river originated Turbidity Currents frequent occurrence repeatedly as seen in the case of Typhoon No. 24 in 2018. The number and the strength of large typhoons hitting Japan tend to increase every year. The probability of turbidity current occurrences are expected to be much higher than by volcanic eruptions or by major earthquakes. However, the observation method of Turbidity Current has not been established yet, and the actual situation is still unclear. Therefore, we have started the development of the Turbidity Current Detector (TCD) that the instrument to observing turbidity currents suppose to be triggered and generated by natural impacts such as Typhoon hitting, Earthquakes, Submarine landslides and some events.
We report TCD, the Turbidity Current monitoring device, to be mounted on the seafloor to observe their behavior such as when and where are the Turbidity Currents generated, how fast are they flowed, how expand and spread are they under the seafloor. The prototype TCD is equipped with function mechanism to take photographs when detected angular velocity exceeds the preset threshold value due to the Turbidity Current occurrence. We have tested and implemented the observation equipped with Camera and Inertial Measurement Unit (IMU) at the actual seafloor, and acquired still pictures once an hour, constant observation of acceleration and angular velocity with 5Hz sampling. Experimental observations were conducted from 2021/08/29 to 2021/11/22, of which records were acquired from 2021/08/29 to 2021/09/16 due to equipment malfunction, and no turbidity currents were encountered during the period of acquisition.
Although there was no typhoon approaching during this year's test observation, there was a problem with the TCD recording stops.
We present the results of a survey on the turbidity currents generated by typhoons in Suruga Bay, Japan.
We also conducted a trace survey of this turbidity current using the R/V Shinsei Maru (KS-21-1 Cruise). The results of this KS-21-1 Cruise will be presented separately in this meeting.
In the cases of submarine landslides such as influenced to Sulawesi Is. (Indonesia), September 2018, or turbidity currents as earthquake off Pacific coast of Tōhoku (Japan), March 2011, both cases associated with large earthquakes, there have been cases where became the source of Tsunami and cause of damages.
In addition, when large typhoons hitting coastal land areas and short torrential rain also become some major cause of turbidity currents, as they supply large amounts of sediment from rivers into the coastal waters in a short period. According to the recent global trend, human casualties are increasing caused by the number of large or super typhoons. First-class Rivers (Fujikawa, Oigawa, Abekawa, Kanogawa) flowing into the Suruga Bay, and the seafloor topography of Suruga bay is quite complicated. Therefore, there is possibility of occurrence of river originated Turbidity Currents frequent occurrence repeatedly as seen in the case of Typhoon No. 24 in 2018. The number and the strength of large typhoons hitting Japan tend to increase every year. The probability of turbidity current occurrences are expected to be much higher than by volcanic eruptions or by major earthquakes. However, the observation method of Turbidity Current has not been established yet, and the actual situation is still unclear. Therefore, we have started the development of the Turbidity Current Detector (TCD) that the instrument to observing turbidity currents suppose to be triggered and generated by natural impacts such as Typhoon hitting, Earthquakes, Submarine landslides and some events.
We report TCD, the Turbidity Current monitoring device, to be mounted on the seafloor to observe their behavior such as when and where are the Turbidity Currents generated, how fast are they flowed, how expand and spread are they under the seafloor. The prototype TCD is equipped with function mechanism to take photographs when detected angular velocity exceeds the preset threshold value due to the Turbidity Current occurrence. We have tested and implemented the observation equipped with Camera and Inertial Measurement Unit (IMU) at the actual seafloor, and acquired still pictures once an hour, constant observation of acceleration and angular velocity with 5Hz sampling. Experimental observations were conducted from 2021/08/29 to 2021/11/22, of which records were acquired from 2021/08/29 to 2021/09/16 due to equipment malfunction, and no turbidity currents were encountered during the period of acquisition.
Although there was no typhoon approaching during this year's test observation, there was a problem with the TCD recording stops.
We present the results of a survey on the turbidity currents generated by typhoons in Suruga Bay, Japan.