Today is the day that we leave the coast behind us and head south towards Rotorua. We have more or less everything we need from up by the Bay of Plenty and are moving south to sample Te Rere, Kaharoa, and Rotorua eruptions. The sun is shining, spirits are high, and we are ready to vigorously sample more pumice after taking a day off to observe the wonders of Whakaari.
Our first stop was actually none of the aforementioned eruptions and we stopped to sample some of the younger Mangaone eruption. This went relatively smoothly, and we headed further south to try to continue on our sampling journey. Our stop was in some logging territory that had been recently clearcut, however some of the eruption units were supposed to be easily visible. We drove up logging road, found where we were supposed to sample, and began to empty out of our vehicles. It was at this point a small pickup truck came ripping up the road and skidded to a halt just in front of us. A very large and aggressive lady stepped out and began ‘politely’ asking us to leave the premises since we did not have a permit to be there. (Logging land in New Zealand is privately owned by individual logging companies and you need a special permit to be there). We promptly obliged, went back down the mountain, and continued on our way. On our way out we noticed that there was a sign at the base of the road that notified us that this was private property and there was to be no trespassing. The only problem with this sign was that it was behind a significant amount of vegetation and not really visible. Oops.
We then moved on to sample the Te Rere eruption along the coast of Lake Rotoiti. This went off without any complications or yelling, so we considered it a success for the day. Lunch was pretty standard for the day, consisting of sandwiches, fruit, granola bars, and some corn chips. New Zealand has fantastic corn chips.
Our final stop for the day was the Rotorua Pumice Quarry. Here they mine pumice for use in making concrete, and let me tell you there is A LOT of pumice. Like…A LOT. Here we were sampling the Rotorua eruption (go figure) and had a beautiful 15m exposure of this eruption. The reason there is so much pumice here, is that we were quite proximal to the vent of the eruption. The closer you are to the eruption, the more eruptive material you will find. This relationship is actually what field geologists use sometimes to help locate vents that may be hidden in the subsurface. After shooting some informative educational videos on physical volcanology here, we were on our way and it was time to make base camp for the evening! The new home for the Tephra Team the next few days is at the Rotorua Holiday Park, and it is quite nice. We have a few cabins to house the squad, complete with small kitchens, bathrooms, and some coin operated laundry. Everyone has come to the consensus that this field work is definitely not exactly near the top of ‘most difficult’ field campaigns in our academic careers. However, none of us are complaining…except for the rotten egg smell in Rotorua. All of the hydrothermal activity in the area makes the air smell of rotten eggs…everywhere.
Goal for today, don’t get yelled at for being where we aren’t supposed to. Also, on a more scientific note…our goal is to sample some of the Taupo Volcanic Center, more specifically the Taupo, Oruanui, and Omega Dacite. Spoiler alert: we achieved one of these goals.
Our first stop was at a beautiful road cut that exhibited both the Oruanui eruption, Hinuera formation, and the Taupo eruption. Our only sample of interest here was the Oruanui and to bag some of the beautiful, large, pumice samples found within the ash flow unit. This unit is 25 thousand years old and erupted 500 cubic kilometers of ‘stuff’. For scale, the Mount St. Helens Eruption was 1 cubic kilometer. That’s a lot of stuff. On top of the Oruanui eruption was the Hinuera formation, which is ash fall derived from the Oruanui. Ash flow units (also called ignimbrites) are derived from erupted ash moving laterally across the ground, whereas ash fall (also called tephra) is the ash that falls from the sky.
After bagging a few bags of soccer ball sized pumice, we moved on to a more ambiguous unit. We believe it is either part of the Taupo or Oruanui eruption, however it has been labeled UNK (for unknown) by the Tephra Team. We did a lot of detailed stratigraphic mapping here, bagged one sample bag, and moved on to Lake Taupo for lunch. Stratigraphic mapping is where you make a ‘map’ of the vertical extent of volcanic units as they exist in the subsurface. This helps you relate the time of eruptions to one another and gives you a frame of reference for where you may be in the volcanic zone’s history (i.e. if you have units A,B,C,D with A being the youngest and D being the oldest, when you find yourself in unit B you know A must be above you and C,D below you).
Lake Taupo turned out to be a beautiful place for lunch, however a toxic algal bloom turned out to be present in the lake and prohibited any swimming.
Post lunch it was time to sample the Omega dacite, do some more stratigraphic mapping, and call it a day. It took a little bit of digging through new soil to find the correct unit that we were in (stratigraphic mapping proved to be a good frame of reference here!) but we ended up getting what we came for.
Upon returning to base camp the team organized samples, did some laundry, ate another good meal, and coordinated the next day’s sampling plan of attack.
All in all, successful and very enjoyable last couple days in the heart of the Taupo Volcanic Zone!
Tomorrow we can take our foot off the gas with respect to sampling and have a more relaxed day. We’re actually ahead of schedule for sampling at this point in the trip.