Ocean rift zone saw spreading happen in a sudden burst

One of the central features of plate tectonics is the formation of new crust at mid-ocean ridges. Part of the spreading process that drives continents apart, it was arguably the discovery of these ridges that drove widespread acceptance of plate tectonics as a theory. Thanks to decades of exploration, we now have a good picture of what the crust that forms at the site of spreading looks like. But we still have an incomplete idea of how its features are actually produced.

In other words, we have a good idea of the outcome of the process, but not a detailed picture of the process itself.

That is starting to change. In 2024, a team of French scientists was able to remotely monitor a major event on the border between the Australian and Antarctic plates, only two months after they installed equipment on the ocean floor. Their data shows that most of the spreading occurred in a relatively short time window, and some key events happened without any obvious seismic activity.

Lots of changes

The site where the events took place is incredibly remote, about halfway between Australia and Madagascar, and far south of India. There’s a large seafloor feature called the Amsterdam–Saint Paul Plateau that rises above the deep ocean plane in the area, interpreted as a rise driven by the presence of a deep ocean hotspot. The rift between the Antarctic and Australian plates runs right through the middle of this plateau.

Despite the indications of a tectonic hotspot, only two volcanic islands are present in the area, Amsterdam and St. Paul. The islands have a long history of failed colonization attempts, accidental strandings, and regular visits by fishermen and sealers. Initially claimed by France, they ended up so useless and remote that France dropped claim to them only a decade later. Forty years after that, the crew of a French ship reclaimed them on behalf of a country that didn’t seem to be certain whether it wanted the honor.