What evidence do geologists have that volcanoes occur on the ocean floor?

Answer 1

Plenty. The biggest is that core samples show iron particles in the floor of the Atlantic to be polarized in north-south "strips". As you move away from the mid-Atlantic ridge in either direction, you get a strip polarized north-south, and then another where strip polarized the opposite way, south-north, and so on ... and these strips match up perfectly for age and orientation on either side of the mid-Atlantic ridge. This discovery led Tuzo Wilson directly to his theory of continental drift. The only thing that could explain this pattern, he said, was if the floor of the Atlantic was growing and spreading over time, and that these polarization patterns were reflecting the polarization of the earth's magnetic field (which flips periodically) at the time that section of floor was formed.

A second piece of evidence, perhaps more compelling for laymen, was his subsequent prediction that an entire chain of successively smaller, submerged volcanic islands would be discovered northwest of the Hawaiian island chain. This is because, he hypothesized, the Pacific plate is drifting northwest over a "hot spot" in the underlying magma that burns its way through, creating volcanoes which create islands. Over time, the plate continues to drift and the volcano goes dormant. The island erodes away, but by then a new island is forming, similar to the effect you might get by passing a sheet of paper slowly over a candle.

Answer 2

Mauna Loa the largest volcano on Earth is one of the Shield Volcanoes that made the island of Hawaii. The base sits on the floor of the ocean and reaches up 9,170 meters forming the island.

Answer 3

Because magma forms at tectonic plate boundaries and most tectonic plate boundaries are underwater.

Answer 4

• midocean ridges
• alternating bands of different magnetic fields appearing nearly symmetrically on opposite sides of midocean ridges
• deep sea trenches
• etc.

Answer 5

ocean ridges