IODP Expedition 360: Starting a Hole to the Mantle
The task is simple: drill a hole through the Earth’s crust to the mantle. However, the last 55 years have demonstrated this is easier said than done; numerous attempts have failed due to a lack of technology, funding, or luck. Expedition 360 of the International Ocean Discovery Program consisted of a determined group of scientists who still trying to accomplish this ambitious goal. It took place during the last month of 2015 and the first of 2016 and I was lucky enough to join them as an Education and Outreach Officer. That means my job was to talk to students and the general public about the science happening onboard the ship in terms that are easy for anyone and everyone to understand.
The expedition was aboard the JOIDES Resolution (“The JR”), one of two scientific drill ships that travel the world taking samples of the seafloor to learn about our planet’s history and composition. The JR departed Colombo, Sri Lanka at the beginning of December and sailed for eleven days to the Southwest Indian Ridge, an undersea mountain chain. Why go to this specific spot? Ocean crust is formed at these mid-ocean ridges all over our planet but this one spreads apart and forms new crust much more slowly than those in the Pacific or Atlantic. This creates large faults (some of the biggest on Earth) and one fault in particular lifted up a section of lower crust to form an undersea mountain called Atlantis Bank; this is what we drilled into. Because the upper crust has been faulted away at this site, we’re taking a shortcut to get much close to the crust-mantle boundary.
Above: The drilling rig aboard the JOIDES Resolution.
This is not the first hole drilled in Atlantis Bank, one of our Co-Chief Scientists, Henry Dick brought the JR here in both 1987 and 1997; the later expedition made considerable progress (it is still the second deepest hard rock hole ever drilled) until an unexpected wave snapped the drill, sending tens of thousands of kilograms of metal free-falling into the hole, permanently blocking it. The reason that he and others are so determined to break through the crust at this site is to test the nature of a layer called the Moho. This is a boundary deep below the Earth’s surface that we can see in seismic waves. It has long been assumed to be the transition from rocks that make up the crust to those that comprise the mantle. However, geologists are starting to think that this may not be true everywhere; at sites like the Southwest Indian Ridge, the Moho may represent the limit of seawater penetrating into the crust. Seawater triggers a reaction called serpentinization, which alters the physical properties of the rock and changes the speed at which seismic waves travel through it. This reaction also produces organic molecules and this has led to speculation that there could be an undiscovered microbial biosphere hiding in the lower oceanic crust.
In my role as an Outreach Officer, I acted as an interface between the science party onboard the ship and interested people on shore. This most commonly was done through live webcasts to classrooms in schools and universities, taking students through the onboard laboratories and giving them a chance to ask their questions directly to the scientists. There was also considerable media interest in the expedition, resulting in many articles both positive (see The BBC, Smithsonian, Nature, and The Boston Globe) and negative (see The Daily Express, but note there are major inaccuracies in this article). These sparked an unexpected number of comments from concerned members of the public including our drilling triggering a volcano or earthquake. We learned that a commonly held belief is that the mantle is a violent pool of magma, ready to burst and the crust is under constant stress, ready to snap. These are not realistic risks but they highlight the critical importance of outreach activities to inform, educate, and allay fears.
After our long transit to the study site, the drilling itself got off to a good start, we began with a smooth setup of a reentry system (so we can get back into the hole after every drill bit change and on future expeditions), after which we made quick progress. The scientists and crew settled into ship life and enjoyed brief holiday celebrations. Everything was going really well… too well. This all changed over a few hours on the evening of December 30th. We knew we were drilling through a fault zone, as recovery of rock samples was low and what we did bring up was fractured into small fragments. Then the drill got stuck; when we managed to pull it back on deck we found three of the four tungsten carbide drill cones that actually cut the rock had broken off and were presumably sitting at the bottom the of hole, blocking our path.
Mere hours later we learned that we had to evacuate a crew member for medical reasons so we quickly prepared the ship for the three day transit required to get within helicopter range of land. After meeting a chopper from the Mauritius police force, we returned to the study site to clean out the hole using a combination of a large magnet and what is essentially a vacuum cleaner for rocks. Doing this and finishing to drill through the fault was difficult and resulted in another broken bit but eventually we got back into solid rock and truly excellent drilling conditions. Tremendous progress was made in the last two weeks of the expedition and we even managed to recover the longest unbroken hard rock sample ever drilled from the seafloor (2.85 m)! There was however one final setback as the expedition ended with a metal ring breaking free from the drill pipe and falling to the bottom of the hole where it now sits.
It was disappointing to leave debris in hole as we steamed away from it but overall things are looking very positive for the future of this site. We drilled 789 m (currently the 5th deepest hard rock hole in the seafloor) and conditions at the end of the expedition were truly excellent. In fact, it has just been announced that The JR will return in just a few short months as it transits from South Africa to Sri Lanka. During this brief stop the metal ring will be fished out of the hole and cement will be pumped into the fault zone in an attempt to stabilize the upper section and maximize the likelihood of successfully deepening it in the future.
Will this be the first hole to reach the mantle? Perhaps. Conditions on Expedition 360 were far from ideal but they also could have been a lot worse. Only time will tell and hopefully the stars will align to bring The JR back to this site for another drilling leg sooner rather than later. As Co-Chief Scientist Henry Dick often said, “drilling is the prefect combination of really high tech engineering and science and pure black magic”.
Lucas Kavanagh is a science communicator originally from Victoria, British Columbia. Aboard Expedition 360 he produced A Hole in the Bottom of the Sea, a podcast with stories and interviews of the science and ship life. You can learn about all his projects on his website and stay up to date by following him on twitter, @lucaskavanagh.
Views expressed in blog posts reflect those of the author, and not necessarily those of the CFES.