T2k-UPLD (Tech-2000 Ultra-Portable Land Drill)
We developed a highly mobile drill rig that is optimized to recover glacial-aged fossil corals and deployed to Espiritu Santo, Vanuatu in Sept – Oct. 2019.
We were in the field for 35 days, and we spent 21 of those days drilling. Meeting with government officials, packing and unpacking the container, transport across the island, and using the system for the first time accounted for the days not drilling.
During the 21 days drilling, we drilled 9 different holes for a total of 107 meters, recovered 77 meters of core, and the deepest hole we drilled was 15.8 meters. While the average drilling rate appears to be ~5m/day, this rate includes the time it takes to break down the drill, move to a new drill site, and set back up again across the 9 different drilling sites.
Normally we stopped drilling at each hole when we encountered marine sediments and were no longer drilling coral reef. We also recovered 19 samples by hand that were exposed on the surface.
In total, we recovered 19 meters of Porites coral that are suitable for climate reconstructions. Ages of coral material ranged from 2,500 years ago at the surface to our oldest age of 15,690 years ago.
We had to travel over three streams and some rough terrain to reach the places we needed to drill.
Our guiding principle for the prototype drill and for the upgrades to Version 2 is that the number of fossil coral heads recovered is directly proportional to meters cored.
The proposed changes for Version 2 center around spending more time drilling and less time transporting and setting up the system at new sites.
Our plan is to replace much of the parts in the prototype that were steel with lightweight aluminum.
Wheeler went into the field and took detailed notes to improve designs on the system so that we can break it down and set it up faster.
We will again use wire-line coring, as this means that the drill rods remain in the hole keeping it open and obviating the need to pull the entire drill string to recover core. We plan to use drilling mud again to stabilize boreholes and maintain reverse circulation to greater depth.
It was no easy task to haul all the equipment to the site, but with the help of some of the locals, we got 'er done.
We used a 20 foot ladder on a steep incline to lower all the equipment down to our location.
We enjoyed getting to know the locals in Vanuatu.
Fossil corals that grew during the deglacial (12-18 ka) and the Last Glacial Maximum (~19,000 to 23,000 years ago) offer ideal records of the El Niño-Southern Oscillation (ENSO) if they could be procured, but are currently under 30-150 m of seawater and meters of sediments, making them inaccessible except by ocean drilling vessels.
Corals grow deeper than the shorelines by up to 30 m, and glacial shorelines were up to 125 m below present. Land-based drilling has successfully recovered fossil corals from uplifted terraces during the last glacial period (Burr et al., 1998; Cabioch et al., 1999; Cabioch et al., 2003; Cutler et al., 2003; Cutler et al., 2004).
However, over the past 15 years, attempts to drill for older ENSO coral records have been neglected due to limited recovery of large glacial to early deglacial corals.
A major problem was that it was impossible to move heavy land-based drills over extremely rugged terrain to the geologically best sites. To address this issue, we built a drill system that can work economically and recover 70 mm cores from corals that grew during the last deglaciation, greatly expanding our ability to study ENSO under changed boundary conditions.
The type of drilling operations we carried out fundamentally differs from ship-based operations (Barbados and Tahiti) and from previous land-based drilling. Land-based operations, like Huon Peninsula, Tahiti, and Vanuatu, successfully drilled on uplifted reefs (Edwards et al., 1993; Bard et al., 1996; Cabioch et al., 1999; Cutler et al., 2003; Cutler et al., 2004), as we are proposing, but drilling sites were severely limited to where a truck could drive or a landing craft could land.
Maximum core diameters from previous drillings were only 45 mm; we are drilling 71 mm cores with our special rig. Ship-based drilling is also limited by water depth and weather, environmental concerns, heave compensation, and expense.
The drill we designed and built can drill virtually anywhere on land, including terrain that a truck or landing craft cannot access.
The relative simplicity and mobility of this system minimizes the costs of using it. The delivery of older corals to present sea level by rapid uplift on Santo means that all of our bore holes would be less than 30 m depth and always within the broader time frame of 12,000 to 25,000 years ago.