WAIS Divide: The Drill
** We have set a US Ice Core Drilling Depth Record. The previous record was 3053.6 m in Greenland. We past that depth at 1 AM on Jan. 18! **
I answered a question about the drill a couple of days ago, and I thought it deserved a more complete post along with some pictures.
We are using the DISC Drill – Deep Ice Sheet Coring Drill. It was designed about 10 years ago for this project. The drill is about 15 meters long.
It’s hard to get the entire drill in one photo, so I needed two. Something you need to know about drilling ice cores is that the boreholes (that the drill travels through) are fluid filled starting about 100 meters below the surface. The fluid is necessary to keep the borehole from closing in on itself. If the hole were left dry, the ice would flow to the borehole (an area of low pressure) causing it to close.
There are four main sections to the drill from bottom to top:
Core Barrel – The core barrel is the part of the drill on the bottom which does the cutting and collects the core. You can see the ice core inside the core barrel. For scale, the ice core has the same diameter as a CD. There are four cutters on the bottom of the drill barrel which spin around, shaving away the ice between the core and ice sheet. The core barrel can fit about 3 meters of ice per run.
To get the core back up to the surface, the bottom has to be broken away from the ice below it. To do this, four “core dogs” are pushed into the core at the bottom. These are the four metal pieces that you can see sticking into the core. These hold the ice core as the drill is raised, causing it to break off from the ice below.
This is the longest section of the drill. The chip screens collect the ice that gets shaved away by the cutter head. That ice has to be removed so that you don’t keep drilling the same chips over and over again. The DISC drill gets the chips up and away from the cutter heads by pumping the drilling fluid through the chips screens. The chips are moved with the fluid and get trapped.
The pump is the curved part just above the chip screen. This is what pumps the chip-filled fluid up through the screens. Above that is the motor which turns the drill. And further above is the instrument section, which has all of the electronics to control the drill. Most of the electronics are actually in the drill itself rather than being up in the control room. The core barrel, chips screens, and the motor, pump and instrument section all spin.
The anti-torque is the fancy name for what keeps the drill in place in the borehole. If you look closely, you can see three pieces of bowed metal (the fourth is hidden). These press against the borehole wall, holding the top of the drill in place and allowing the cutter head to cut rather than just spin in circles.
So there are the main portions of the drill. One last part I need to mention is the cable.
The cable is not only what lowers and raises the drill, but it also runs the power and communication channels down to the drill. You can see the cable is not wrapped cleanly in this photo. This caused about an hour delay, all because one little screw on the winch became loose.
In about 20 minutes, WAIS Divide will be the second deepest ice core ever drilled. I’m about to head down to the arch to see it come through. Pretty exciting – 3271.2 m
More on ice cores in a future post!