Drill rig servicing day

The night crew drilled to a depth of 805 ft last night.  Today the day shift drill crew serviced the rig, changing its oil and filters and performing other routine maintenance.  Meanwhile, the core processing team boxed rock to 737 ft and logged core boxes to 371 ft. 

One of the more interesting finds from processing today's rock was an intrusion only a few feet thick.  This intrusion (rock above the fracture) is almost glassy at its top and bottom margins, and has invaded a weak point in an olivine-rich flow (rock below the fracture).  Although this intrusion is thin and does not necessarily indicate on its own that we are drilling near a rift zone of Mauna Kea, the high abundance of extremely vesicular pahoehoe flows suggests that the lavas we're drilling through didn't travel very far before they covered the area beneath the drill site. 

Because it is so vesicular, the rock core doesn't have much internal strength and can't hold itself together well.  Fragments of rock break loose from the sidewalls and cave in onto the drill pipe, making the drillers lift up the drill string a bit and then re-drill back down on that cave-in material until the sidewalls of the hole are clean.  Drilling loose cave-in material quickly eats away at the drill bit, head driller Ron Fierbach estimates that we've had to change the bit every 150 feet or so since we started drilling shield-stage lava flows.  Changing the bit is a time-consuming and tiring process for the drillers, as all the drill pipe has to be pulled out of the hole. This process is also expensive, each bit costs $800 and the drill hands are tripping pipe in and out of the hole instead of the bit cutting on bottom and extracting more rock.  Bit life in the less vesicular Hawaii Scientific Drilling Project lavas averaged many hundreds of feet, with one bit cutting over two thousand feet!  We'll be keeping our fingers crossed for a slight change of lava type that would enable such drilling conditions again.