Crust and rock sampler

 Crustal and rock samples are collected by crushing or scraping crust and rocks using a sampler. Since most of the seafloor is covered by sediments, it is necessary to precisely locate exposed seafloor areas such as ridges in order to collect rock samples. In addition, such terrain is often so rugged that the sampler often gets caught, requiring different observation and maneuvering techniques from those used when handling mud samplers. Here we introduce some rock-related sample collectors.

・Chain-bag dredge

　A chain-bag dredge is a collector that combines a net made of metal chains and a mud box, which is towed over a rocky seafloor or ridge to scrape off and collect samples. It is similar in shape to a biodredge, which collects organisms living in the sediment, but uses a net made of chain so that it will not be destroyed by rubbing on the hard seafloor. The collector is towed by moving the vessel forward once it reaches the bottom of the sea floor. Another method is to collect sediment and rock samples simultaneously by using a combination of a chain-back dredge and a cylindrical dredge as shown in Figure 1, where the seafloor is mixed with sediment and rocks. Since the dredge drags over an uneven seafloor, the collecting instrument may get caught on the seafloor. Therefore, the tension on the wire is constantly monitored during the observation, and when an abnormal tension is observed, the collector is retrieved by using the ship's maneuvering technique so that the collector is released from the seafloor.

　Fig 13　chain-bag dredge

・Rock corer

　The rock corer is a metal pipe with a weight at the top and a metal fixture for crushing and collecting rock at the bottom end. The collector is impacted onto the seafloor, where the crust and rocks are exposed, and the crushed sample is collected by sticking to the grease applied to the tip of the instrument and the side of the weight. It was developed to collect even a small amount of rock samples from the seafloor, where towing a dredge is dangerous due to the jagged and complex topography, such as ocean ridges.

　　　 　Fig 14　Rock corer