We had anticipated that it would take sixty dredges to sample the nine ridge segments within our ~200 mile-long study area – and indeed, that is the exact number of dredges we did! And to our delight, we found that we had a bit of time left since the crew and scientists had been more efficient than expected.
So, with our remaining time, we turned our attention a bit to the south to tackle a scientific problem concerning the Galapagos microplate (GMP). Rotating at the end of the Cocos-Nazca spreading centre, the Galapagos microplate had been studied previously but there were holes in the data. Its southern edge includes a deep trough, called the Dietz Deep, which transitions into a ridge that is 30 miles long, 5 miles wide and 2000 feet high called the Dietz Volcanic Ridge. Bob Dietz was a close colleague of Harry Hess so it is natural that that the ridge and deep were named after him. There was a big snag, however, no one had shown that the Dietz Volcanic Ridge actually is volcanic. That could only be confirmed by dredging.
Now dredging is a bit like Goldilocks’s bowls of porridge: some dredges bring back too little rock, some bring back too much and most bring back just the right amount. We had some Father Bear dredge hauls on Dietz Volcanic Ridge with huge chunks of pillow lava or, in the most spectacular case, one monster slab of lava. This came perched on the top of the dredge mouth and the wire tension showed it weighed around 1000 pounds. How could it ever have tidily set itself right on top of the dredge? We could not even move it across the deck. So we collected significant portions of it, photographed it and, reluctantly, returned much of it back into the ocean. Sad but necessary.
Did we answer the big question? You already know the answer to that, which is a resounding yes. We made three dredges on and around the ridge and all brought back lava, so it is volcanic. But more than that, much of the lava was very fresh, the glass sparkling in the sun. So it is an active volcanic ridge, not just an old volcanic one. That is an important step forward in understanding the Galapagos Microplate. A great use of our extra time!