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Visiting Google Maps, I came across this long, sinuous, while pretty regular mark undersea that looks like an ancient river, when the sea was way lower, or a big (big!) boulder that could have rolled down to the bottom (?).

Given the location (ring of fire), it could also be a "crack" made during a major (and ancient) earthquake that, with time, has been filled with sediments.

This looks like this question, but the shape is very different, and much less sinuous than the one in Japan.

The mark:

enter image description here

The location:

enter image description here

JeopardyTempest
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Déjà vu
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1 Answers1

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It looks like a submarine canyon incised into the seafloor and shelf by repeated sediment "flushing". Given the location, earthquakes probably flush huge quantities of sediments from the low angle plains to the north, through the canyons, and into the abyssal plain to the south. You might find these canyons in any tectonically active seafloor that sees heavy sediment loading from, say, a mountainous tropical region. This one's not that big, compared to New Zealand's Hikurangi Channel, at nearly 700 km.

There's another one off the SE coast of Hokkaido Island. What, precisely, locally controls the formation of these canyons is an interesting question.

Fred
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Knob Scratcher
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    There are canyons like this on the passive margin along the US Atlantic coast, so I'm not sure a tectonic explanation is necessary. – Spencer Mar 17 '21 at 18:57
  • True, but those canyons are likely drowned fluvial channels created by Pleistocene continental runoff. By contrast, Shionomisaki Canyon does not seem to have any surficial river associated with it. – Knob Scratcher Mar 18 '21 at 19:48
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    There are three in the upper left of the image, coming down from the higher level of the continental shelf. In the Atlantic, the abyssal plain has continuations just like Shionomisaki Canyon. – Spencer Mar 18 '21 at 22:05