NOAA Ship Rainier completes hydrographic surveys in Southeast Alaska

By Ensign Airlie Pickett

In early June of this year, NOAA Ship Rainier headed up the inside passage to Southeast Alaska to conduct hydrographic survey operations in two project areas. The first, Tracy Arm Fjord, is located in the Tongass National Forest and is home to a number of glaciers making it a popular destination for tourists and the cruise ships and sightseeing vessels that carry them. From 2014-2015, a little over two million out-of-state visitors traveled to Alaska, bringing over $4 billion and 39,700 jobs to the state. Nearly half of those visitors arrived via cruise ships (Alaska Department of Commerce, Community, and Economic Development, 2016).

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Location of Tracy Arm Fjord and Lisianski Inlet in Southeast Alaska.
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Bathymetric data collected by Rainier in Tracy Arm Fjord.

The area was last surveyed in 1974 using only partial-bottom coverage techniques. Since then, technology has improved vastly and complete bottom coverage is now possible. Rainier and her five survey launches are equipped with multibeam echo sounders, which provide a much greater density of soundings, from which a highly detailed 3-dimensional surface can be created.

At the far ends of the Tracy Arm Fjord are two glaciers, the Sawyer Glacier and the South Sawyer Glacier. Satellite imagery (and in-person investigations) reveal that over the past few decades the glaciers have receded significantly, leaving a large area of completely unsurveyed water directly preceding the glaciers.

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Previously unsurveyed area overlaid with an image of Rainier’s newly gathered hydrographic data. At the Sawyer Glacier (left), Rainier collected new hydrographic data approximately .75 miles past the previously surveyed area, and at the South Sawyer Glacier (right), she sailed a full mile into uncharted territory.

The survey was conducted in early summer, and the warm weather made itself known. Both glaciers began to calve in earnest and strong glacial currents and prolific icebergs made this survey operationally challenging. In addition, the high canyon walls of the fjord impeded communications, making it difficult for the ship and her survey launches to maintain contact.

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Two of Rainier’s launches operating in the iceberg laden waters of Tracy Arm Fjord. Credit: Amanda Finn, Survey Technician, NOAA

The data collected from this survey will also be used by glaciologists, providing a highly detailed 3-dimensional view of the path taken by the glacier as it receded. Rainier’s data reveals ridges across the seabed at several points along the fjord.  These features, called moraines, are formed where glacier recession stopped for a period of time.

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A well-defined moraine located just before the junction between the two arms on the east side of the fjord.

 

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Rainier in front of the South Sawyer Glacier. Credit: Ensign Collin Walker, NOAA

The second survey completed by Rainier during this time was in Lisianski Inlet, home to the town of Pelican, population: 88. Lisianski Inlet is a popular location for recreational boaters and yachts as well as being an important route of the Alaska Marine Highway ferry system. The area was last surveyed in 1917 using lead lines. Rainier’s full-bottom coverage using multibeam sonar will greatly enhance the accuracy of local charts and assist local mariners in safe navigation.

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Bathymetric data collected by Rainier in Lisianski Inlet.
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One of Rainier’s Survey launches underway in Lisianski Inlet. Credit: Amanda Finn, Survey Technician, NOAA

 

One thought on “NOAA Ship Rainier completes hydrographic surveys in Southeast Alaska

  1. While aboard a mid-sized Holland-America cruise ship two years ago this month, the decision was made by the skipper to stay out of Tracy Arm because of the amount of calving ice at the face of the two tidewater glaciers and the extent of the resultant bergy bits there. Instead, we proceeded on into Endicott Arm and were rewarded by the magnificence of Dawes Glacier, also a retreating tidewater glacier.

    Interestingly, Lisianski Inlet was named by Dr. William Henry Dall, in 1879, in the (USC&GS) Coast Pilot, after Capt. Federovich Lisianski, upon whose chart of 1814 it first appears. (Ref. Baker’s Geographic Dictionary of Alaska)

    Charles A. Burroughs, Captain, NOAA (Ret.)

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