Hotspots are like the strong, silent type. On the surface it is obvious they are very powerful, but it is difficult to find out what is going on with them underneath the surface, because there is no way to force your way down there. Until someone builds a vessel out of unobtainium that can travel through the earth’s mantle, to get to know a hotpot, you have to look closely at the rocks it produces at the surface (though, seismic waves help as well). One of the main reasons the JOIDES Resolution is on this expedition is to try to get to know the hotspot that created the Louisville Seamount Trail a little bit better.
Most likely, there is a mantle plume down underneath the Louisville hotspot. Mantle plumes are really hot magma that is thought to rise up like a mushroom cloud from the boundary between the Earth’s core and the mantle. They reach the lithosphere (the crust and uppermost portion of the mantle) and, if they melt through to the surface, form a volcano or a chain of volcanoes.
For decades, mantle plumes were thought to be completely stationary in the mantle, but research on a JOIDES Resolution drilling expedition (ODP Leg 197) showed that the Hawaiian mantle plume has not been sitting still. Since then, computer models have predicted that the Louisville mantle plume has also been moving. Right now, the science team onboard the JR is looking for evidence in the Louisville seamount rocks to see whether this is true or not.
Other new research has been showing that not all hotspots have a mantle plume underneath them. Shiki Machida, one of the volcanologists onboard, has done research that shows that some small hotspot volcanoes (called “petit spots”) are occurring in places where the ocean plate is being bent. Cracks form in the lithosphere there, allowing small amounts of magma to seep through to the surface. Alex Nichols, another volcanologist onboard, has done research that shows that water in the mantle may be playing a more significant role in the formation of some hotspots than previously thought (water causes rock to melt at lower temperatures). Volcanologists not currently on the ship have been finding other explanations as well that suggest that hotspots may result from varied causes.
The scientific method that is allowing us to better understand hotspots has been hugely successful in expanding our knowledge of the world. One of the reasons for this is that scientists never assume they already know everything. They are constantly asking new questions and making new observations that increase our understanding. For a nonscientist like me, it is exciting to play a small role in that process as we attempt to uncover some of the mysteries of hotspots.
In the photo: Shiki (one of the Expedition 330 volcanologists) in a long distance relationship with the Louisville hotspot, trying to get to know it better by studying the rocks it produces. Photo by Christoph Beier.