A primitive but effective tool we sometimes use for collecting rock samples from the seafloor is this heavy-duty chain bag we call a rock dredge. Here I am rigging the ropes and chains for our first deployment of an Antarctic expedition. The dredge is connected to a cable trailing behind the ship so we can drag it across the bottom scraping up whatever loose rocks are around. While this is usually a reliable method for collecting rocks, it provides little information about what the seafloor looks like. And if we find two or more different types of rocks in one dredge haul we have no idea exactly where they came from along the dredge track because they are all mixed together in the chain bag by the time the dredge is back on the ship. That is why we have to use a submersible such as Alvin to collect rocks if we truly hope to understand how a geologic feature on the seafloor formed.
Related Links
