Phase 2 of the RAID project entails construction, assembly and testing of the RAID drilling platform, through to staging in Antarctica for future scientific operation on the East Antarctic ice sheet. In anticipation of future readiness, a field trial with the RAID system is planned in Antarctica during the 2016-17 summer field season. Having tested what we can in North America, we are conducting the Antarctic Field Trial (AFT) in thick firn and ice in order to validate our operational plan, evaluate full integration of the drilling system in a deep-ice setting, and learn from drilling operations in order to prepare for science drilling as an autonomous, traverse-capable system. Antarctica is the only place to effectively integrate the entire drilling system and evaluate the capability of those components designed for operation in thick firn and ice.
In order to prove the operational capacity of the RAID system, goals of the AFT include traversing over snow, site set-up, augering of firn and installation of casing, drilling through thick ice, retrieving ice and rock cores, rigging down, stabilizing the borehole, and redeploying to a base station. Specific goals are outlined below.
The AFT in 2016-17 will take place in the area near McMurdo Station, in order to take advantage of the established USAP transport and logistics system, thereby reducing risk, cost, and footprint in Antarctica. The RAID equipment was shipped to Antarctica in late 2015 and off-loaded at McMurdo Station in January 2016. After wintering over, the AFT will commence in late 2016 after the RAID equipment is moved from winter storage to the nearby ice shelf, where it will be loaded onto ski platforms. After a traverse from McMurdo, the RAID system will be set up for drilling at a site near Minna Bluff [see figure]. After completion of the AFT, the equipment will be winterized on snow berms at Williams Field in anticipation of a future traverse to South Pole. The RAID field trial will be conducted autonomously from McMurdo and other Antarctic services in order to provide a realistic exercise of future science operations, but the close proximity to McMurdo will provide a backup of mechanical, field, and medical services if needed.
The primary criteria for selecting a site to conduct a field trial of RAID are simple — thick, grounded ice. Ideally, a suitable location should be accessible for multiple ski-module deployment, within relatively short traverse range, and be fairly flat with no steep slopes. The ice plateaus on the south side of Minna Bluff provide the best location for a full-scale field trial of the RAID drilling system [see figure]. At Minna Bluff the ice has a thickness of about 600 m, is easily accessible by traversing across the Ross Ice Shelf along the established South Pole traverse (SPoT) route, and rises gently above the ice shelf at two small ice plateaus, all within a point-to-point distance of about 90 km. Depending on route chosen, the traverse distance is <200 km and is expected to take about 3 days transit from McMurdo.
The region near McMurdo Station is primarily underlain by rocks of the McMurdo Volcanic Group, chiefly alkaline basalts exemplified by the eruptive units on Ross Island, Mt. Erebus and Mt. Discovery. Minna Bluff is a narrow, 45 km-long ridge extending southeast from Mt. Discovery, a Miocene alkaline stratovolcano. The main rock types are basanite and phonolite containing large (up to 5 cm) kaersutite and feldspar megacrysts, abundant comagmatic inclusions (kaersutite-rich), and rare mantle xenoliths. Since the late Miocene, Minna Bluff has been a terminal pinning point for the Ross Ice Shelf and is a local topographic barrier helping to block the Ross Ice Shelf from flowing into McMurdo Sound. Eruptions of alkaline basalt occurred between about 8-12 Ma, during which time lavas partly interacted with ephemeral glacial ice. Minna Bluff is surrounded by thick, relatively stable ice of the Ross Ice Shelf, which extends to McMurdo Station.
Radargram of line Y39a from north to south across Minna Bluff and the flank of Black Island, showing location of the primary RAID drilling site A1. Radar data provided by Duncan Young (University of Texas Institute of Geophysics) as part of the GIMBLE project.
Airborne ice-penetrating radar (IPR) data were recently flown across this area by the University of Texas-Austin to image the edge of the Ross Ice Shelf in the vicinity of Minna Bluff, White Island and Black Island. A representative radargram is shown (see figure), which transects the eastern of the two small ice plateaus and the eastern flank of Black Island. On the southern end, this record shows the transition between thick ice overlying water in the Ross Sea and bedrock of Minna Bluff. A grounding line is visible at about -45 km (at the surface break in slope). The very intense, flat reflector at about -400 m depth is the base of floating ice over seawater, and shows strong multiples (reflected radar waves) below. The rougher reflector toward Minna Bluff is the grounded ice interface. Internal reflectors within grounded ice show a continuous record of ice accumulation banked against bedrock. AFT site A1 is our primary target for the drilling trial because it has greatest thickness (≥600 m) and lies farthest from subglacial water of the Ross Sea.
The primary objective of the Antarctic Field Trial is to probe the RAID system’s ability to operate successfully as an integrated whole instrument in a realistic, thick-ice environment. RAID is a complex system whose components have been individually tested, but experience shows that a successful system is much more than the sum of its components. For this reason whole-system testing is crucial. Personnel are also very much a part of this system, and the field trial will give us an opportunity to assess field team integration.
For practical reasons, the lack of deep ice in North America has precluded a realistic test of the deep-borehole fluid circulation, the airlift process, and other unique facets of RAID. Although completion of the North American Test in Utah in early 2015 required successful integration of key RAID components, the test facility simply could not reproduce Antarctic deep-ice conditions. Computational fluid dynamics modeling indicates no fluid pressure problems, but given the importance of deep ice drilling to the future success of RAID a real-world field trial is needed.
Also, the speed of penetration and other RAID operational steps must be measured for overall RAID planning purposes and ultimate success in the deep field, and this is only possible in a realistic setting. At the same time, a trial is best done in a low-marginal-cost and low-risk environment, rather than directly on the East Antarctic ice plateau. Taking into consideration all these factors, we settled upon a field trial near McMurdo at Minna Bluff as the best compromise between realism, cost, and risk.
The Antarctic Field Trials in 2016-17 provided an invaluable opportunity for drillers to learn in the harsh environment of Antarctica. The Minna Bluff site is legendary for its sudden storms (“Herbie Alley”), yet it is relatively close to McMurdo in the event of a true emergency. Safety is the number one priority of RAID operations, and the field trials provided an excellent chance to flag potential safety concerns and implement mitigation of safety issues.
The RAID concept fundamentally embodies speed, with a design ultimately intended to produce 5 holes to bedrock per season. This translates to a design goal of about 40 hours to drill through 3000 m of ice. Therefore, one important objective of the Antarctic field trials is to measure how fast RAID can penetrate thick ice, including all the pipe handling and fluid recirculation system connections and disconnections. With only 600 m of ice at Minna Bluff, the comparable duration at this speed would be 8 hours. Because the ice thickness is slightly more than 600 m, a small increment of ice at the bottom of the borehole can be used for further tests of the ice coring and airlift systems.
A multitude of other small tasks must be performed in a nimble fashion if RAID is to ultimately succeed and deliver scientific discovery at a high rate. We have defined a full list of criteria that will be evaluated for determining success of the field trials, including many speed-related benchmarks. These are provided in section 6 of the AFT Field Plan [download PDF].