Posts Tagged ‘ice cores’

The Stuck Ice Drill Saga; the team completes drilling

Monday, February 1st, 2010

The LARISSA ice core team has successfully drilled an ice core to bedrock (extending from the surface of the snow/ice to the Antarctic rock surface), reaching 445.65 meters. The team took less than a month at a campsite (Site Beta) in Antarctica to finish the job. During this time, the team experienced trouble with two drills used to recover ice cores. Being in the middle of a vast field of ice in Antarctica, the team had to use ingenious engineering tactics to work around problems. The story is included below:

Saga of the “stuck” Electrical-Thermal (ET) drill

“The LARISSA Bruce Plateau Science Team has the goal of drilling an ice core to bedrock (estimated to be 425 meters) on the Bruce Plateau in the Antarctic Peninsula. At approximately 2:00 PM on Thursday January 21 we experienced a seizure of the ET drill and it could not be extracted from the drill hole. The heating element (see photo) on the head of the drill that melts through to recover the ice core stopped heating because the heating element burned out due to water leaking into the coil. Immediately upon the “burnout” event the fresh meltwater at the head of the heater (at the very bottom the hole) froze in roughly 10 seconds and locked the drill in place at the bottom of the hole, which was 384 meters below the surface.

The initial approach was to pour several gallons of glycol-anti-freeze along the drill cable so that most of it would be delivered to the top of the drill. This was not successful and we determined later it is not a good practice as the glycol-anti-freeze dispersed on the top of the 130-meter thick column of ethanol-water solution. Thus it had virtually no impact. Quickly it was determined that the only chance of success would be to deliver the glycol-anti-freeze directly on top of the drill as was done by our team when the ET drill became trapped at about 380 meters during the 2002 drilling of a core to bedrock on the Bona-Churchill expedition. The different between these 2 situations is that on Bona-Churchill, there was no cable connected to the drill, but on Bruce Plateau the cable was still connected to the top of the drill. Thus, all of our efforts to reach the top of the drill had to also take into account the cable in the 130 mm diameter borehole. Several devices were designed and tested to pass through the 138 meter thick column of ethanol-water solution to deliver the glycol-anti-freeze directly on the top of the drill. At the same time there was concern that the borehole might begin to close due to ice flow or the diameter might be reduced by the formation of “slush” somewhere between the top of the ethanol-water solution column and the drill. In this case, even if we were to free the drill at the bottom we might not be able to bring it to the surface through a constricted borehole. We lowered and raised our bailer system multiple times to check the borehole diameter. We found that the diameter of the borehole was slightly constricted at about 288 meters depth. The reason for the constriction is not precisely known but was likely associated with a buildup of slush. Basically, we had two problems to overcome: (1) free the drill from the bottom of the borehole and (2) enlarge the diameter at the constriction so the drill could return to the surface.

Modifying a pump used to filter the ethanol-water solution and placing it into the bailer allowed ethanol to be squirted at the top of the constriction and then again at several other depths below the constriction. Next our bailer was modified to work not as a bailer which takes in water, but as a glycol-anti-freeze delivery system. The bottom of the bailer was redesigned to include a valve with a small activation rod that opened the valve when the rod touched the top of the drill. The bailer was then filled with the glycol-anti-freeze and delivered to the top of the drill. About 9 liters of glycol-anti-freeze was delivered to the top of the drill in two different runs. Subsequently, the drill cable was placed under tension and after waiting about 36 hours, the ice around the bottom of the drill had melted enough that the drill separated from the bottom of the borehole and could be raised to the surface (see photo). Interestingly, the drill barrel contained 66 cm of ice (see photo) that had been drilled before the drill became trapped. Our best estimate is that only 1 to 2 cm of ice was dissolved by the glycol-anti-freeze that settled at the bottom of the borehole (end of the drill).

This entire process, from when the drill became stuck to retrieving the drill safely to the surface, required almost exactly 5 days. During this time we received glycol-anti-freeze from Rothera and the Nathaniel B Palmer (ice breaker ship) that was working nearby in Berilairi Bay. In addition, the OSU team made numerous modifications to the equipment they had on hand with limited machining capacity. For example, the bailer that is normally used to take liquids from the borehole was modified to deliver glycol-anti-freeze to the top of the drill, to check the diameter of the borehole and to deliver a specific quantity of ethanol to multiple specific locations along the borehole wall. As just one example of the ingenuity required – we had no hose of the proper length and diameter to deliver the ethanol using the pump that was available. Thus the wires on the inside of a spare piece of drill cable were removed and the sheath on the drill cable was connected to the pump and placed in the bailer for ethanol delivery.

The drill was recovered at approximately 11:00 AM on January 26, it was repaired by 2:00 PM the same day and the team recovered 10-meters of new core before the end of the day. The photo shows the nearly 2-meter long piece of ice core that was drilled on the first run after the drill was extracted.

EPILOG: In the afternoon on January 31, 2010 the LARISSA ice core team’s electrical-thermal drill reached bedrock at a borehole depth of 445.65 m. The three photos, all taken on January 31, 2010, show (1) a nearly 2-meter long section of core recovered just above the bottom of the hole, (2) the last piece of core recovered from the borehole and the LARISSA drill team upon completion of drilling to bedrock on the Bruce Plateau, Antarctic Peninsula.”

Updates for January 21st

Thursday, January 21st, 2010

From Ellen Mosley-Thompson on the ice core drilling progress: “Today we reached 350 meters in the long hole that is expected to be 425 m (± 5 m) deep.”

Here is a photo of one of the 2 meter ice cores that have been recovered: