Happy Easter! Farther down the rabbit hole we go...

We have been logging the past few days because of some drilling issues that needed to be taken care of.  A couple nights ago, some sticks found their way into the mud tank and blocked the flow of drilling mud into the hole.  Below is an image of what happens to a drill bit when there is no mud lubricating the cutting face (these are PQ drill bits with an inner diameter of 3.378 inches):

 The bit on the left is "used" and needs to be replaced.  The bit on the right is "abused" and has had its cutting teeth ripped off by turning on bare rock without drilling mud to lubricate the cutting face. Here's another view to illustrate the point:

Note that the bit on the right is also bowed beneath the teeth, a response to the weight of the drill string on top of the bit as it tried to cut without the help of drilling mud. 

The drill crew was able to recover from this issue, and after spending yesterday doing maintenance on the rig, we are back to standard coring operations. 

Logging from post-shield to shield stage

Today we changed gears from core processing and logged 20 core boxes, completing from Box 57 to Box 76.  This was interesting work, as we probably covered some of the earliest post-shield material of Mauna Kea and then got to the shield-stage lavas that we will continue to log for the rest of this hole. 

Please feel free to browse the newly uploaded high-resolution box photos in our archive, we have added through Box 100 today (there is a link in the Photos tab above)

The ash deposit

Today we processed rock core to a depth of 1198 ft.  The weather has been cooperating and we can dry the boxes of rocks in the sun before photographing and logging them.

Speaking of photography, we finally got a decent picture of the ash I've been mentioning lately.  For a sense of scale, the rock shown here is 3.5 inches across.  Feel free to click on the photo to look at the ash beds in greater detail.  The cross bedding seen in the upper left of the picture might just be a surface scratch, I didn't notice any other cross bedding.  This is by far the finest and most well-bedded ash we have seen so far, from a depth of ~950 ft below the surface.  Such ash is an indicator of an explosive eruption, which is an eruptive style thought to be relatively uncommon from Hawaiian volcanoes.  However, there are a number of historical accounts of explosive eruptions from Kilauea volcano, as well as ash deposits found all over the island that date long before the first Polynesian explorers arrived.  Such fine ash can be carried far by the wind, so we can't say yet which volcano may have produced it. 

Another day, another 83 feet of rock core

Today we processed rock core to a depth of 1118 ft, and received nine more trays of rock at the end of the day.  We will start processing again right away tomorrow morning; lately the drilling seems to be proceeding a bit more smoothly than before.

Apologies again for no photo of the finely bedded ash, I'm working on getting a good close-up shot of it under good lighting conditions.  

Over 1000 feet of core processed!

We processed rock core to 1035 ft today, only 5000 or so more feet to go before the first hole is finished!  Over the past 10 days, the drill crew has penetrated over 750 ft for an average of ~75 ft/day. The average run length has been just over seven feet, less than the maximum ten feet because there has been so much loose material that has been blocking the core barrel and causing early run pulls to the surface.  This drilling rate is as good as can be expected, considering how fractured the rock has been. 

My apologies for the lack of a photo in today's update.  I took pictures of some fine ash beds that we saw today when logging, but the lighting was poor and the photos are all too dark.  I'll post a picture of this layered ash tomorrow.

We rock the dock

Today we processed rock core to a depth of 947 ft, and the trays that were dropped off at the end of the day will carry us over the 1000 ft mark.  As always the rocks were interesting to interpret, but I forgot to take a picture of anything photogenic.  Instead, here's a look at yesterday's lineup of full core trays at our loading dock:

This isn't even all the trays we processed yesterday, there are more on our work table that you see on the far left.  Each core tray is six feet long and has a painted top end, so the drill crew can extract the rock into the tray in proper vertical orientation.  The trays also have circular foam end pieces to keep the rocks from sliding out, and tray covers to prevent rocks from bouncing out of the trays during transport to UH Hilo from PTA. 

The effect of intrusions

Today we processed a lot of core, to a depth of 858 ft.  Last night, the drillers were able to advance downward a significant amount because the rock was so loose that they could push right down through it without the bit having to cut much.  You may recall that they encountered conditions like this before, when we drilled through what we believe was the cinder of a cinder cone.  However, this time the loose rock was created by a different process.

The photo above (co-worker's hand for scale) shows the bottom contact of an intrusion that measures ~16 ft thick.  The rock on the upper side of the photo has been welded together, but the rest of that unit is intensely broken (as unconsolidated as the cinder we encountered earlier in the hole).  Similarly, the rock above the intrusion is also broken to a cindery mush.  The intrusion itself is in great shape, as you can see by the unbroken nature of the lower part of the core shown in the photo.

I think that this intrusion caused the breakup of the rock above and below it, both fracturing it and baking it (there is abundant, black baked olivine in the rock above and below the intrusion, not to mention the intense baking of the loose rock fragments themselves to a bright orange color).  In addition, there may have been groundwater in the vesicular rock that was invaded, which was turned to steam by the intrusion's heat.  The expansion of this steam probably contributed significantly to baking and breaking apart the surrounding rock, particularly above the intrusion where the most extensive baking is found. 

This intrusion is different from the one described yesterday in that it is at least five times thicker.  Yesterday's intrusion didn't significantly affect rock above and below it, because it was thinner and cooled more quickly.  Both intrusions support the idea that we are drilling in an area not far from the eruptive source of the lavas that the drilling is sampling.