How is a big lava flow going to change plate tectonic theory?

Per this story.

Huge underwater lava flow mapped - Japanese deep-sea vessel explores Pacific wonders

Vulcanism, whether from no-kidding volcanoes or from shield lava flows, generally results from subduction zones, where two plates are colliding.

From the description, I’m not sure if the East Pacific Ridge is the same thing as the Nazca Ridge, both being underwater “highlands” off the west coast of South America.

But present theories of plate tectonics suggest that the Pacific Ocean floor off the coast of Central and South America is mostly comprised of two old plates, the Cocos Plate to the north and the Nazca Plate to the south, the Pacific Plate being further out to sea. The Nazca Ridge, IIRC, marks the demarcation of the Naza and Pacific Plates. I believe that the Andes are considered to be the result of the subduction of the Nazca Plate under the South American Plate.

This vulcanism would indicate that some subduction is occurring between the Nazca and Pacific Plates, probably with the Pacific Plate riding up and over the Nazca Plate. But I’m not clear how that changes present theories of plate tectonics – I was under the impression that that was the present theory, with the Nazca Plate, like Poland in WWII, being eaten away at from both sizes.

One story is all there is on this? That’s a real stealth mission the Shinkai 6500 has going there!
From what’s available, I think the surprise here was finding a large flood eruption in a subduction zone. Vulcanism in subduction zones is generally regarded as being of the explosive variety due to the large amounts of water that get taken down to the mantle along with the sinking plate.

I don’t see where “world’s largest lava flow” comes from. The Columbia River Plateau flows were far larger. Here’s an article that describes one that’s 130km by 240km and another listing several flows of over 10k sq miles.

And the Deccan flows might have been 10 times larger than those.

Those guys need to take a ride with a geologist from Portland to Boise.

I didn’t pay close attention to that phrase, but now that you mention it, I take it as a bit of non-technical reporter hyperbole. Somebody probably said, “the world’s largest underwater lava flow” (and I don’t know if it is or not) and the reporter ran with it, missing the key word.

Anyway, aren’t the Siberian Traps even larger than the Idaho and Deccan flows?

Lava flows occur not just in subduction zones, but also in areas of divergent spreading (mid-ocean ridges) and hot spots such as the Hawaiian and Galapagos Islands (which often form shield volcanoes).

I think they are actually talking about the East Pacific Rise, which is the spreading boundary between the Pacific Plate and the Nazca and Cocos Plates. The East Pacific Rise is an area of ultrafast sea-floor spreading, and thus an area of extensive lava flows. The Nazca Plate is being subducted under South America, but the west side of it is a spreading center. The “Nazca Ridge” is neither a subduction zone nor an area of sea-floor spreading, but rather a ridge running east to west in the middle of the Nazca Plate from Easter Island to southern Peru. It has been produced by lava flows from the Easter Island hot spot as the Nacza Plate has passed over it.

The article cited in the OP really doesn’t contain enough information to tell what exactly they are going on about. The bit about “changing theories of plate tectonics dramatically” is no doubt an example of an editor condensing the original article into near meaninglessness.