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Fieldwork

An Inside Look at Eroding Coastal Bluffs on Alaska’s North Slope



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In September 2015, scientists from the U.S. Geological Survey (USGS) and the University of California, Santa Cruz (UCSC) surveyed rapidly eroding permafrost bluffs on Barter Island, a remnant of low-elevation tundra on Alaska’s Arctic coast. Warming air and sea temperatures in the Arctic are leading to longer periods of permafrost thaw and ice-free conditions during the summer months, which can weaken the coastal bluffs and increase their vulnerability to storm surge and wave impacts. The 2015 survey is part of a long-term effort to document seasonal to decadal coastal-bluff change on the island’s north coast.

Large map shows Barter Island on Alaska’s North Slope
Above: Large map shows Barter Island on Alaska’s North Slope. LRRS, Long Range Radar Site. [larger version]

Close-up map shows study sites on the coastal bluffs.
Above: Close-up map shows study sites on the coastal bluffs. [larger version]

In spite of bleak weather conditions that thwarted scheduled flights to Barter Island for many days, the survey team achieved its goals on the island. The researchers drilled into the permafrost to obtain samples of permafrost ice, pore water, and sediment. They are using geochemical techniques, such as measurement of radon and stable isotopes, to trace the movement of groundwater and examine its effects on sediment erosion. Several geophysical techniques were used to image the subsurface structure of permafrost features, such as ice-wedge polygons, and to measure the salt content and internal structure of materials that make up the frozen ground.

Repeat electrical resistivity tomograms (ERTs) had been collected on the coastal bluffs in Barter Island in early and late summer 2014 to evaluate the effects of one summer’s thaw cycle. ERTs provide a cross-sectional view of electrical resistivity within the bluffs. Because ice is a poor conductor of electricity and thus has high resistivity, ERTs reveal the distribution of subsurface permafrost. ERTs were collected from the same bluffs during the 2015 survey to examine annual change and to identify sites for drilling into the permafrost.

Repeat electrical resistivity tomogram (ERT) images
Above: Repeat electrical resistivity tomogram (ERT) images collected on the coastal bluffs of Barter Island reveal the effects of one summer thaw cycle. Hotter colors indicate high resistivity values, which in this case likely represent low-conductivity permafrost. ERT profiles were collected along the same transects during the 2015 fieldwork to examine annual change and to identify sites for drilling into permafrost. [larger version]

To complement these geo-electrical methods, the September 2015 survey team collected data with a phase-sensitive radio echo sounder (pRES). Whereas traditional echo sounders send sound waves through water to detect boundaries between materials with differing physical properties, the pRES sends radio waves through ice. pRES data can be used to image the base of an ice mass and also internal reflecting layers, such as layers of liquid water or variations in the size of air bubbles in the ice. The USGS researchers were particularly interested in another strong radio-wave reflector: the interface between freshwater and saltwater. They collected pRES data along select survey lines for comparison with the ERTs to determine where the subsurface gets salty and so document the influence of seawater in permafrost.

A primary focus of the 2015 effort was to ground truth the remote-sensing methods by collecting permafrost samples. A custom-designed drilling platform allowed the team to obtain samples from depths down to approximately 6 meters in permafrost. Preliminary results confirm that the permafrost pore-water salinities near the bottom of the cores exceeded seawater values, an observation supported by the 2014 and 2015 ERT images. The pore-water samples from these drill holes are being used for additional geochemical analyses to illuminate the oceanic and geologic evolution of this dynamic coastal environment.

Eroding coastal bluff on Barter Island.
Above: Eroding coastal bluff on Barter Island. [larger version]

The researchers aim to document seasonal to decadal coastal-bluff change and associated hydro-geologic processes along a 3-kilometer stretch of coast on Barter Island by using the techniques outlined above along with recently collected time-lapse photography; historical maps and imagery; GPS surveys of the beach and nearshore; sediment sampling and analysis; 3-D models of the terrain derived from aerial photography and airborne lidar (a laser-based surveying technique); photographs of the bluffs taken from an all-terrain vehicle (ATV); measurement of water levels, currents, and salinity in lagoons and nearshore waters; and numerical models of waves, storm surge, and inundation.

Sea ice and frozen shoreline Ice-free and wide beach
A: [larger version] B: [larger version]
Summer storm from the west eroding the beach Late-summer extreme storm with waves crashing into the bluff
C: [larger version] D: [larger version]
Above: Photographs from a mounted time-lapse camera looking eastward along Barter Island’s north shore document how the coastal bluffs and beach changed during a single summer. The photographs show: A, Sea ice and frozen shoreline (June 15, 2014). B, Ice-free and wide beach; dark-colored material on beach is fine-grained sediment eroded from bluffs (July 10, 2014). C, Summer storm from the west eroding the beach (July 25, 2014). D, Late-summer extreme storm with waves crashing into the bluff (September 3, 2014). View the complete time-lapse sequence at http://walrus.wr.usgs.gov/climate-change/time-lapse.html.

The Barter Island study is part of a larger investigation of climate-change impacts on Alaska’s Arctic coast. (See website, “Climate Change Impacts to the U.S. Pacific and Arctic Coasts: Research” and related Sound Waves article, “Northern Alaska Coastal Erosion Threatens Habitat and Infrastructure.”)

Left, researcher drilling and coring the interior of the bluff to ground-truth geophysical methods. Right, core section filled mostly with ice.
Above: Left, Cordell Johnson drilling and coring the interior of the bluff to ground-truth geophysical methods. Right, a core section filled mostly with ice. [larger version]

Scientists who contributed to the September 2015 survey included Peter Swarzenski, Bruce Richmond, Cordell Johnson, Tom Lorenson, Li Erikson, and contractor Amy West from the USGS Pacific Coastal and Marine Science Center, and Neil Foley and Slawek Tulaczyk from UCSC. The work falls under USGS projects on Coastal Aquifers and Climate Change Impacts to the U.S. Pacific and Arctic Coasts.

Essential support for this field effort was provided by aquatic biologist Greta Burkart and Arctic National Wildlife Refuge (ANWR) Manager Brian Glaspell, both of the U.S. Fish and Wildlife Service (USFWS). On the last day of fieldwork, Bruce Richmond was asked to give a briefing to USFWS Director Daniel Ashe, Senator Tim Kaine (D, Virginia), Senator Martin Heinrich (D, New Mexico), Deputy Regional Director of Alaska Region USFWS Karen Clark, and Brian Glaspell.


Related Sound Waves Stories
Northern Alaska Coastal Erosion Threatens Habitat and Infrastructure
July–Sept. 2015
Erosion Doubles Along Part of Alaska's Arctic Coast—Cultural and Historical Sites Lost
May 2009

Related Websites
Climate Change Impacts to the U.S. Pacific and Arctic Coasts: Research
USGS
Coastal Aquifer Project
USGS
Climate Change Impacts to the U.S. Pacific and Arctic Coasts
USGS

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in this issue:

Fieldwork
Investigating the Offshore Queen Charlotte-Fairweather Fault System in Southeastern Alaska

Eroding Coastal Bluffs on Alaska’s North Slope

Artificial-Gas-Seep Test Produces 3D Images of Bubble Plumes

Sandwich Beach Cam Established

Spotlight on Sandy
Hurricane Sandy: Three years later

Outreach
USGS St. Pete Center Participates in Great American Teach-In

Fifth Annual St. Petersburg Science Festival

Meetings
A-ICC Training Courses on Ocean Acidification

Publications
Dec. / Jan. Publications

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