I've seen a new report that suggests these are deposits from the Theia collision.

Hawaii is made up of a chain of volcanoes . Volcanoes are rock , melted at excessively high temperatures , even under the ocean , creating both lava tunnels and solid mountains . So yes , there are underground areas of thicker materials than conitinents are normall constructed of .

Three cheers for curiosity. Without it, we would have neither science nor scientists.

Interesting article

I don't know what @yvilletom is talking about. The paper was published in Science. That's not self publishing. They aren't speculating that the structures are made by aliens or anything like that. They are just looking at the composition of the deep Earth.

What you read in publications whose owners publish what they think people want to read is not science; it’s opinion or speculation. Don’t believe it.