National Geographic

Rediscovering Ross Island 2012: “G-092 Redeployed to CONUS”

Written by Ken Sims.

“G-092 redeployed to CONUS” (the Continental United States). This Antarctic vernacular sounds almost Orwellian, but essentially it means that after five great weeks in Antarctica, our 2012 Ross Island Expedition, dubbed G-092, is drawing to a close.

Plate 1: Group photo taken on our last day camping at Cape Bird. From left to right- Phil Kyle, Erin Phillips Writer, Dan Rasmussen, Paul Wallace, Ken Sims and Glenn Gaetani. Photo by Dan Rasmussen.

It is bitter sweet to have our expedition come to its end. I will miss the camaraderie of my good friends and colleagues and the excitement of scientific discovery (Plate 1); however, I am also very happy to be back home with my family. I know this sentiment is universal amongst us all.

Plate 2: Aerial photo looking into the summit crater of Erebus volcano. Mt. Terror’s north slope is in the background. Photo by Ken Sims.

Since returning from camping out at Cape Bird, the major focus of the final phase of our expedition was to sample the flanks and summit of Mt. Bird and to finish up a few key sites around Mt. Terror and Hut point. We were extremely busy sampling until the very last day, including one day of flying a double shift when Glenn and I flew out to sample the Erebus Fang Ridge late one night (Plates 2 and 3).

Plate 3: Young parasitic cone on the lower west side of Fang Ridge on Mt Erebus. From an aerial perspective this young eruptive cone’s lava flows look like an octopus draped over a hill. Mt Bird and the Ross Sea are in the background. The summit of Mt Bird is directly behind the cone, Cape Bird, where we camped, is on the left, and the un-sampled lava flows of Lewis Bay are on the right. In the foreground, Ken Sims swings a sledgehammer to collect a fresh lava sample and Glenn Gaetani obtains a sample bag from the helicopter’s side basket to properly archive the sample. Photo by A-Star pilot Paul Murphy.

All told, it was an extremely successful expedition. Sure there were a few storms, including the “Herbie” Glenn discussed in the last blog, but for this time of year we were extremely lucky – we had only four days when the weather was so bad that we could not sample. Our coverage of the volcanoes Mt Terror, Mt Bird and Hut Point Peninsula was more complete than we planned for or even hoped for (Plates 4 and 5); in total we collected more than 120 lava samples which amounts to about 1500 pounds of rock.

Plate 4: Ross Island showing Mt. Bird, Mt. Terror and Hut Point Peninsula around the dominant and larger Erebus volcano (note the radial symmetry). Symbol and number indicate the sites sampled during our expedition. This image shows the extensive sampling we conducted on the flanks and summit of Mount Terror, the summit of Bird, most of which had never been sampled or examined. Image from Goggle Earth.

Despite our overwhelming success sampling most of the exposed volcanic flows and eruptive cones throughout the volcanoes of Ross Island, the inaccessibility of the Mt Bird lava flows exposed in the sea cliffs around Lewis bay left a significant hole in our data set. These flows, which were unreachable because of thin and rotten sea ice underneath and calving glaciers overhead, represent the best material to characterize the early basaltic lavas erupted from Mount Bird. They have never been sampled before, so there are no archived samples to work with.  However, to fill in this obvious void of key samples for our study, we are working with the National Science Foundation to return with a small team (myself and another experienced mountaineer) for a very short expedition at the very beginning of the season next year, when the sea ice should be much thicker (essentially we would start working in the early Austral fall when the helicopters start flying).

Plate 5: Aerial view looking up the East Ridge of Mount Terror. This photo shows some of the numerous lava flows and eruption cones that were sampled during this expedition. Photo by Ken Sims.

In addition to collecting a whole lot of unique samples for further study, we made a lot of interesting and exciting discoveries regarding the geology of the Mt. Terror, Mt. Bird and Hut Point volcanoes. We saw what we interpreted as magma mingling, we discovered new mantle xenolith locations, and we found lots of amazing pyroxene and amphibole (kaersutite) megacrysts in the numerous lava flows and tephra cones that we sampled. It is even fair to say at this early stage of our research that the mineralogy of the lavas we sampled support our hypothesis, namely that Ross Island is the manifestation of a mantle plume where the outside of the Erebus plume has a different chemical composition than its interior.

Plate 6: Backscattered electron image (BSE) and Ca element map of a single anorthoclase mega crystal from Erebus volcano. The darkest areas in the BSE image are the anorthoclase crystal. The abundant irregular areas, slightly brighter than the anorthoclase, are melt inclusions. Other included mineral phases are pyroxene (light grey phase on Ca map), apatite (next brightest on BSE, highlighted in red on Ca map) and magnetite (brightest in BSE, dark on Ca map). Taken from Sims et al., 2012; Journal of Petrology;

But the ultimate test of our hypothesis will be when we quantify the chemistry of the lava samples back in our laboratories at the Universities of Wyoming and Oregon. After the rocks arrive by ship to the CONUS this spring, Erin and Dan will: process the lava samples; identify their exact mineralogy using optical and x-ray microscopy; dissolve them in strong acids; measure their chemical and isotope abundances using plasma mass spectrometry; and, measure the volatile content of the deep magmas that were trapped in the growing crystals before the lavas erupted (Plate 6). So much to do, so much to learn; our exciting discoveries will continue…

Acknowledgements: It is essential to recognize and even salute all the support we received to make our expedition successful.  None of our scientific research program would have been possible without the National Science Foundation Polar Programs and the US Antarctica Support Personnel. Everyone who worked with us to organize and implement this trip, both in McMurdo station and in the United States were amazingly helpful, very efficient and always extremely pleasant to interact with. We can’t thank everyone enough!