Measuring Waves and Permafrost to Better Understand Erosion on Alaska’s Arctic Coast
Two groups of U.S. Geological Survey (USGS) scientists traveled to Barter Island off Alaska’s northeast coast in July and September of 2018. They installed video cameras overlooking the island’s outer shore and measured properties of the frozen soil, called permafrost, that strengthens the coastal bluffs. Their work is part of a USGS project to better understand erosion along the U.S. Arctic coast—erosion that threatens Native Alaskan villages, sensitive ecosystems, energy- and defense-related infrastructure, and large tracts of Native Alaskan, State, and Federally managed land.
Video station records coastal events
In July, the team installed thermistors to measure permafrost temperatures and a video system to record images of the beach and the breaking waves. Oceanographer Shawn Harrison of the USGS Pacific Coastal and Marine Science Center (PCMSC) designed the solar-powered monitoring system. It uses video cameras attached to a small computer to record and quantify processes such as wave run-up, development of rip channels, bluff erosion, and movement of sandbars and ice floes. The video images can even be used to map the shape of the seabed beneath nearshore waters. All these factors can be measured by traditional methods, but the video system—modeled after the “Argus station” developed at Oregon State University—has the advantage of collecting data almost continuously over long periods and in conditions, like storms, that make traditional data gathering difficult or dangerous.
Harrison installed the video system on a Barter Island bluff with the help of technician Cordell Johnson and project chief and research oceanographer Li Erikson. Atop a tall pole they placed two cameras, one facing north over the Arctic Ocean and one facing east along the shore. Below the cameras they buried a small seismometer to record vibrations caused by breaking waves. They put two wave gauges attached to small buoys immediately offshore. One of their goals was to combine the data from these instruments to test the possibility of remotely estimating wave heights—an important factor in coastal erosion—without maintaining wave gauges in the ocean.
In September 2018, Harrison and Johnson returned to Barter Island with oceanographer Ferdinand Oberle and PCMSC Director Guy Gelfenbaum. By the time they arrived, the wave-gauge buoys had disappeared, one of them dragged away by an ice floe. Local residents and colleagues from the U.S. Fish and Wildlife Service are keeping an eye out for the gauges, which could wash ashore and yield valuable data.
During the September fieldwork, the crew downloaded data from the thermistors, seismometer, and video cameras; made repairs; and strengthened the structure supporting the video cameras. They also repaired and fortified the mounts for four “game cams,” sturdy cameras that take photographs of the bluffs and shoreline at regular intervals. Although these cameras provide only images—not the rich datasets amassed by the video monitoring system—they have proven useful over the years for recording the presence or absence of shore ice (which tends to protect the coast), slumps along bluff faces, and large waves that undercut the bluffs. (For example, view a time-lapse sequence of photos taken during summer 2014.) One of the game cams looks toward the video system, which helps the scientists keep an eye on it remotely from their Santa Cruz, California, offices.
The video cameras captured the motion of waves and ice floes during numerous autumn storms, until frigid temperatures in early October made the battery too weak to power the system. Collaborator Will Wiese (a biologist with the U.S. Fish and Wildlife Service) put the battery and solar panels into storage in late November, as daylong darkness set in. The cameras are still on the mast, and the USGS team hopes to re-activate them in time to capture ice breakup in the spring. The rugged game cams were also left in place.
Distribution of permafrost within the bluffs
Another task for the team in September was mapping the permafrost in the coastal bluffs. Led by oceanographer Oberle, the scientists collected an unprecedented number of electrical resistivity tomography (ERT) profiles—spanning the entire length (about a mile and a quarter) of the Barter Island bluffs. ERT images provide a cross-sectional view of the ground’s electrical resistivity—how resistant it is to the flow of electricity. Electrons move easily through water in the soil, but not through ice, which is a poor conductor. Because of ice’s high electrical resistivity, ERT profiles give scientists a detailed picture of ice-rich permafrost within the bluffs.
Project scientists have collected ERT data from Barter Island bluffs every September since 2014 to monitor changes in the permafrost. This year’s collection spans a longer stretch of bluffs than ever before. Geophysicist and former USGS contractor Jason Greenwood (now with Advanced Geosciences, Inc.) helped Oberle process the data into one continuous profile.
Oberle wants to measure how much frozen water is locked up in Barter Island’s coastal bluffs and where the ice is concentrated. The melting of this ice, especially large pockets of nearly pure ice, can potentially cause severe erosion. It could also explain the recent opening of crevasses, or “sinkholes” as locals refer to them, that pose a falling hazard. Oberle reported that these crevasses—some as deep as 26 feet—are a new feature on Barter Island since he began working there in 2016.
Sharing knowledge about Barter Island
The USGS scientists hosted community outreach events in July and September to present results from earlier studies and to hold an open-floor discussion of their ongoing research. These events provided an opportunity to exchange knowledge and perceptions of the many coastal processes occurring along the shores of Barter Island. Local government officials, residents, and visitors attended. The USGS scientists particularly appreciated the information, insights, and concerns about the changing coastline offered by long-time community members.
On the way home from Barter Island, Gelfenbaum gave a talk to the National Research Council’s Ocean Studies Board, which was meeting in Fairbanks to discuss Arctic infrastructure issues. Gelfenbaum presented background information on Arctic coastal geology, recent and historical shoreline-change data, and findings from USGS studies of Arctic coastal processes.
View additional photographs of the July and September fieldwork.
in this issue:
Understanding Erosion on Alaska’s Arctic Coast