I had an excellent day on the Rangitoto drillsite recently. There is nothing like being one of the first people to see something that hasn’t seen the light of day in hundreds (or even thousands!) of years! We’re talking about rock that is much speculated about, rock that will hopefully answer pressing questions about Auckland’s volcanic future: this rock is IMPORTANT (and full of clues, as Tamzin says.). So yes, I am not ashamed to say that I was geeking out the entire time.
The above picture shows what the inside of a core box looks like when it is filled. Depth markers are noted, and the box is filled from right to left. Rangitoto is composed of thin lava flows such as this one. The top of the flow is top right, and is marked by red oxidized/weathered and very vesicular (full of gas bubbles) lava. The lava gets denser as we go deeper into the flow, with less gas bubbles. It then transitions back to very vesicular lava at the base of the flow (not pictured here). Flows seem to get slightly thicker as they drilled deeper (this would be a ‘thicker’ flow at 105 – 109 m).
The main aim of drilling is to get samples of all the lava from the top layer to the original seafloor below. This would mean that we have the entire sequence and history of Rangitoto in the spot that was drilled, and can piece together how long the volcano has been erupting, perhaps why it was erupting, and how it has been erupting (off and on or continuously?). As sea level is around ~120 m depth, geologists onsite are expecting to see a transition from lava into seafloor around that point.
The day that I went to observe the drilling, they drilled from ~104 to ~115 meters. It was the 6th day of drilling. It is expected to continue for a few more days.
Once drillers have broken through the lava layers to the original seafloor, drilling will continue to be sure that there is no lava lurking underneath, and to hopefully reach the rocks that lie under most of Auckland, called the Waitematas. At that point, we will know that we have cored the entire eruption sequence from start to finish!
Here are some highlights from my day:
All photos by Elaine Smid.