Peter joined GSSI in 2016 as the archaeology and forensics application specialist, as well as a member of the training and technical support team. He is a member of the Register of Professional Archaeologists and specializes in terrestrial geophysical methods applied to archaeology, geographic information systems [GIS] analyses, and submerged prehistoric archaeology. Peter brings a wide range of GPR experience to the GSSI training team. He has conducted GPR surveys on six continents, and in the US and Canada has carried out over seventy terrestrial geophysical surveys on archaeological sites and cemeteries. Here, he discusses his experience in traveling to McMurdo Station to conduct specialized training for crevasse detection.

Q. Tell us a little about the circumstances of why you went down to conduct training.

Glaciated landscapes are dynamic environments and continental ice sheets are constantly changing.  In Antarctica the United States Antarctic Program [USAP] is responsible for moving supplies and personnel across hundreds of miles of snow and ice. They usually travel along established routes, but the ice and snow can shift and crack leading to crevasse formation. In a yearly traverse to the south pole from McMurdo Station, and for occasional scientific expeditions, USAP uses GSSI GPR equipment to avoid crevasses and other ice/snow hazards. This year I traveled to McMurdo Station to train USAP employees in the setup and deployment of GPR for crevasse and snow/ice hazard detection.

Q. How is this different from other onsite trainings that you’ve done?

A typical On-Site training is a two-day class at a customer’s facility or job site. This involves an initial day of travel, two 8-hour training days, and a final day of travel. Two days of training works well for typical GPR applications, like concrete and utility investigations. The classes are focused on data and interpretation rather than environmental variables. The Antarctica training was quite different. Data from polar regions are, for the most part, fairly straightforward. The GPR profiles reveal well-layered ice and snow, and potential subsurface hazards exhibit abundant hyperbolic tails and air voids that contrast with the well-layered background.  Additionally, glacial ice/snow is so resistive that a 400MHz antenna can penetrate 100+ feet (in New England soil conditions the 400MHz reaches 10-12 feet). The environment was extremely cold, making it a challenge to set up and monitor the equipment.

SIR 4000 screen image showing 400MHz data in Time Mode.
These data showed a deep (50ft) sequence of Antarctic ice and snow layers split by a crevasse.
The crevasse exhibits dipping upper fill layers suggesting it was once exposed at the surface but has since been filled by snow.

The Antarctica training comprised three different back-to-back classes. The first was a one-day class for advanced users who had previous experience using GPR for crevasse detection. The second and third classes ran for two days, and they covered introductory GPR method and theory for first-time GPR operators. These classes also had a field component, where we mobilized the GPR and Pisten Bully to identify crevasses in real-time.

Q. What was traveling down there like?

The travel was like most other international trips I’ve had, though the flight times were considerably longer. The flight from Boston, MA to Houston, TX was around 4-5 hours, but the flight from Houston to Auckland, New Zealand was a grueling 15.5 hours. This trip also came with expectations of potential lengthy delays. Aircraft arriving in the McMurdo vicinity land at Phoenix Airfield, a large runway constructed on the ice. With highly variable weather, strong winds, and heavy snowfall the airfield requires constant maintenance to make it safe for landing. When I arrived in Christchurch, New Zealand I expected to fly to McMurdo two days later. I ended up with a 6-day delay, and then finally departed on the 5.5-hour flight to Phoenix Airfield. However, due to the changing weather we could have easily “boomeranged” back to Christchurch because of unsafe conditions. Fortunately, the weather cooperated. I was supposed to fly to McMurdo on a military C-17, but I ended up flying in a commercial jet. This was a huge bonus because there were lots of windows. On the inbound approach I was able to see vast expanses of sea ice, and closer to the continent I saw multiple ice streams and other glacial features. I was also excited to see Mount Erebus, an active volcano that produces rare Erebus crystals (formed from anorthoclase feldspar; only found in Antarctica and Africa).

Q. What were the conditions of the survey?

Each of the two-day introductory classes had a field component that prepared students for real-time detection of crevasses and other ice/snow hazards. Antarctic GPR surveys typically use a SIR 4000 control unit a 400 MHz antenna to conduct real-time monitoring of the subsurface traverse conditions. The 400MHz antenna is placed into an inflatable ring (for protection) and is then mounted on a rigid framework/boom extending 20 to 25 feet in front of a Pisten Bully. A long control cable runs from the 400 MHz antenna to the inside of the Pisten Bully where it connects to the SIR 4000. The length of the antenna boom provides adequate time to detect a crevasse/hazard before the Pisten Bully crosses it.

The overarching goals of the field exercise were to familiarize participants with the setup and optimization of the SIR 4000 and 400 MHz antenna, and to refine their ability to identify crevasses in real time. Since the stakes are quite high (the safety of traverse and science personnel) the training exercises had to be representative of actual field conditions.

If the operator spots a potential crevasse the Pisten Bully’s driver is notified, and the vehicle is stopped. The GPR operator and the driver will then work together to establish the orientation and size of the crevasse. This usually involves backing up and approaching the crevasse from different angles and across parallel tracklines; this provides a good estimate of the direction and width of the target. After some additional calculations the team decides whether they can safely cross the crevasse, or if they need to avoid it and look for a safer route.

Q. Did anything unexpected occur during your training?

Aside from lengthy delays (not entirely unexpected), the training went quite smoothly. I was highly impressed by the participants; they were very enthusiastic and quickly mastered the concepts. I was surprised by the beauty of Antarctica. I’m originally from Maine, and I’ve seen my share of snow and extreme winter conditions, so I anticipated a typical winter landscape. I was totally wrong. Antarctica has a vastness and scale that can’t be appreciated from maps or globes. It leaves you feeling overwhelmed by majestic snowy vistas, near-constant daylight (during southern hemisphere spring/summer), and the realization that you are a long way from home. My time on the ice helped me to understand what the original explorers must have faced and helped me appreciate the drive and determination of everyone who works in Antarctica today.

Q. Would you go again?

You bet! Traveling to Antarctica was an amazing adventure, and I met some great people in New Zealand and at McMurdo Station. I see all GPR projects/research as continuing education opportunities, and the Antarctica training was all that and more. Plus, I checked off my sixth continent for GPR data collection!