Week 6: Erebus Perimeter

The PASSCAL team finished installing all Erebus Perimeter stations.

The Erebus crew (Avi and Alan), fondly known as the "Octopus Bois" by the helitechs, took me along to finish the Erebus Perimeter installs.

The "Octopus Boi" moniker originated from this slingload configuration. Photo credits: Avilash Cramer.

There are 3 sites in the Erebus Perimeter network, located at Cape Royds (ROYDS), Trachyte Hill (TRACH), and Oamaru Peak (OAMA). The sites make a triangle around the base of Mt. Erebus.

The all-caps site designations are used in seismic/infrasound metadata to identify which site the data comes from. The convention is to use a 3-5 character alphanumeric code to identify the site, and a 2 character code to identify the network. The Perimeter network uses 8H.

Labelled map of Ross Island. Red stars are Erebus Perimeter sites. Yellow stars are the test site near Castle Rock and McMurdo Station, for reference. Original image from Wikipedia, modified in powerpoint by me :)

The three Perimeter sites had already been installed (ROYDS, with my help, TRACH, and OAMA), but we had a few changes to make at TRACH and ROYDS. We loaded up the Bell 412 helicopter (the larger of the 2 types of USAP helicopters) with minimal equipment -- a few grey boxes of equipment and some tools, plus our personal gear and ECW.

So much leg room compared to other trips I've taken! No extra equipment to carry along!

Crevassed and broken-up ice near the base of Erebus out the helicopter window.

We landed at TRACH, also known as Trachyte Hill, located near Cape Bird. Thus named because it is made of trachyte, a type of volcanic igneous rock (meaning it is formed from lava that extrudes onto the surface and cools, as opposed to plutonic rocks formed from magma that intrudes and cools underground). Trachytes are made of a fine-grained matrix, formed by rapid cooling on the surface, with large crystals of different minerals embedded within (also called phenocrysts).

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I didn't get any up-close images of the rocks (I know, I know, but I'm a geophysicist, not a geologist, let me be), but you can see the reddish-brown color of the rocks from the pictures I did take of the site.

A picture from the Trachyte Hill site, with Erebus in the background.

At the site, we needed to swap the datalogger for a different one. Avi and Alan had accidentally installed a model that only has 3 channels for data collection, which correspond with the 3 masses inside the seismometer (one oriented N-S, one E-W, and one vertical). However, all Perimeter stations have a seismic sensor and an infrasound sensor, which provides an additional channel of data. We swapped the 3CH model for a 6CH model, and all was well.

Opening the enclosure (large orange box) to swap the datalogger. We checked everything out on our laptop to make sure the site was still functioning and transmitting data.

Bell 412 helicopter parked at the site. The orange dome protecting the seismometer is just visible on the right of the image.

We also added more rocks around the base of the enclosure and on top of the conduit protecting the cables, to make sure they didn't blow around in the wind.

Avi walking to grab some rocks to weight down the solar cable.

We took some group photos, then climbed back in the helicopter to fly to the next site.

Left to right: Alan, me, and Avi. Framed by two tripole lampshades. I'll talk more about this style of solar panel mount in just a bit. Photo credits to the helicopter pilot, Ryan.

Sea ice breaking up outside the helicopter window on our flight from TRACH to ROYDS.

Once we landed at our site at Cape Royds, Avi realized that we had accidentally left behind the toolkit that he meant to bring. We had some tools, but he worried that it wouldn't be enough. The helicopter was going to leave us and fly back to McMurdo, so Avi decided to fly back with the helicopter, and would bring the tools we needed when it came back to pick us up. In the meantime, Alan and I would do what we could.

The goal was to add tripoles to each of the lampshade solar panels. We had originally installed the lampshades with 3 guy wires, but the mothership back at PASSCAL realized that it would be more secure if we added the 3-legged tripole mounts to the solar panels, as well.

Luckily, with a bit of ingenuity and imagination, Alan and I were able to improvise with the tools that we had and re-installed the solar panels before the helicopter came back. And we even finished with a few hours to spare!

Possibly the best picture of me ever taken. I am tightening the bolts on the tripole legs with a vicegrip and ridiculously large adjustable wrench. Not the intended tools for the job, but it did the trick!

Me posing with the newly-installed tripoles. Not pictured: when I lost my balance and nearly faceplanted into the tripole leg.

Another view of the Cape Royds site. Left to right: infrasound windscreen (shiny aluminum), orange seismic sensor dome, orange electronics enclosure, and two tripoles.

After we checked the site and weighted down the conduit with more rocks, we had a few hours to burn before the helicopter came to pick us up. We could see a mysteriously pale-colored rock in the distance, and as any two geophysicists would, we hiked out to it to check it out. Also, like any two geophysicists, we named the rock.

Me posing with Mysterious Jay, the mysterious rock.

As it turns out, the mysterious light colored rock in the sea of dark was a giant chunk of granite! It was likely deposited here by moving glaciers.

Proper geology picture with my glove for scale. This was the most perfect granite specimen I have ever seen. Like, straight out of a textbook perfect.

We hiked back up to the camp where the penguin scientists were still living, stopping on the way for more rock hunting. The lava produced by Mt. Erebus is pretty unique in its composition, anorthoclase phonolite.

Phonolite is a type of felsic rock (meaning that it contains mostly light-colored minerals high in silicon, oxygen, and aluminum; contrasted with mafic rocks containing dark-colored minerals high in iron and magnesium). However, phonolite does not contain any quartz, a mineral common elsewhere. 

Anorthoclase refers to the chemical composition of the type of feldspar mineral contained in the Erebus magma. If you've heard of "Erebus crystals", these are just large pieces of anorthoclase feldspar that form on Erebus. I found a few really nice ones around our site. Feldspars have two planes of cleavage at 90° (aka planes that the mineral is weak and breaks easily along), and when they are formed nicely, they make perfect rectangular prisms. Super cool!

Really pretty anorthoclase feldspar crystal showing off perfect 90° cleavage.

The penguin scientists kindly cooked dinner for us again. This time, a delicious chicken and veggie stew with cheese toast. The cheese toast had OREGANO on it, which I have never thought to try but it completely changed the cheese toast game. I am only having cheese toast with oregano from now on.

Plus oreos for dessert!!!!!

As you may have gathered by now, I am a silly person. Alan is nearly as silly as I am, and we sang/yelled loudly the entire time we were working. When we came up for dinner, the penguin scientists noted that they could hear everything we were singing the entire time, and were "a little concerned" when they heard us screaming. But they decided that if we were really hurt, there would probably be a lot more screaming, and they didn't need to check it out.

The helicopter finally arrived to pick us up, along with Avi and several bags of tools. But we told him we had managed without, and the three of us climbed back in to fly back to McMurdo. And with that, the entire Erebus Perimeter network was completed!!