The very first time I really thought about ice core drilling, I couldn’t picture how it worked. To me, a drill is something that just makes a hole, like a drill you use to hang something on the wall in your house. I’ve had a few friends ask about it too, so I am clearly not the only one. So, here’s a short intro to how it works!
The drill barrel is a hollow tube, with three cutters around the edge. As the drill goes down into the ice, it is cutting a circle around what will become the ice core.
A view of an ice core inside the drill barrel, freshly pulled up from the ice. You can see the three cutters around the edge.
Drilling into ice produces what we call “chips” - tiny pieces of shaved ice that look like snow, just like how sawing wood produces wood shavings. Those ice chips will clog up the drill if they are not given anywhere to go, so the outside of the drill barrel has a spiral called a “flight” that the ice chips slide up along as the drill goes down.
We drill one meter at a time, lowering the drill into the ice using a long cable on a winch. Our ice core drillers monitor the depth, speed, and tension of that winch, which gives them information about how the drilling is going down there.
One of our drillers operating the Blue Ice Drill
When the meter of ice is completed, the driller will then reverse the winch, quickly enough to engage the core dogs and break the bottom of the core. The core dogs - so named because they bite! - are spring-mounted and have a sharp edge that rotates and digs into the ice.
Once the core comes up, the drillers then have to separate the core barrel from the body of the drill (the sonde) and then push the core out of the barrel. Here are a couple of videos of that process from our smaller-diameter drill:
Drilling has been going really well! Our Blue Ice Drill hit bedrock at 91 meters last week (check out the COLDEX video of the inside of that borehole!) so that drill is finished for now. Based on data previous cores drilled nearby, that core should have ice from 3 million to 5 million years old.
The smaller drill (pictured in the videos above) is expected to go to 300 meters. As of last night we were at 160 meters. This drill is called the Shallow Wet Drill, because it is capable of using drilling fluid. We started out with dry drilling and waited until core quality degraded before adding the fluid, which happened at about 114 meters deep. Fluid drilling is commonly used for deep ice core drilling projects but that has never been tried at Allan Hills before now. The drill fluid, a biodegradable solvent called estisol, helps improve core quality by making the drilling process smoother and preventing fracturing in the cores due to pressure in the borehole. The cores have been extremely high quality ever since! The downside is that the estisol gets everywhere, has a strong odor, and stays very very cold (about -30 degrees C) without freezing, but I think it is worth it for the good cores!